1 Introduction

Great interests are devoted to spinel ferrite materials (SFs), particularly with the commencement of the second millennium. Chemically formulated, MFe2O4 is a sub-class from the spinel structures which displayed quite remarkable superparamagnetic, electrical, and optical characteristics reflecting their unique composition [1,2,3,4,5]. Reducing the crystalline size in the nanoscale region plays a key role in enhancing the structural, magnetic, electronic, and optical properties of SFs [6]. The MFe2O4 classification commonly relies upon the location of M2+ cations relative to Fe3+ ones in tetrahedral and/or octahedral sites [7]. While M2+ cations are tetrahedral and Fe3+ cations are octahedral, normal spinels are obtained; meanwhile, M2+ cations are octahedral and Fe3+ cations are octahedral/tetrahedral, inverse spinels show up, and for random distribution [8] of M2+ and Fe3+ cations, complex spinels are found. Concurrently, metal cations’ locations are dependent upon their affinity and consequently the stabilization energy, their ionic radii, the synthesis technique that controls the morphology of the resultant specimen, and the reaction conditions. Many [9] Ni2+ [10], Co2+ [11], Zn2+ [12], Mn2+ metal-based SFs have been investigated revealing amazing magnetic, electric and optical properties that are highly appropriate for different critical industries. Many researchers have synthesized and characterized different spinel ferrite structures such as MFe2O4 (M=Co [13], Cu [14], Mn [15], and Zn [16]). As a consequence of their ultimate resistivity and Curie temperature, SFs are interesting magnetic materials with a wide range of technological applications and environmental stability. It is essential to adopt the proper crystalline characteristics as well as the proper choice of synthesis routine that will define the crystal lattice structure and its chemical composition, which would eventually produce quite enhanced properties for the new structure. Different techniques such as the sol-gel [17], co-precipitations [18], hydrothermal [19], mechanical method [20], facile sol-gel approach [21], micro-emulsion method [22], and thermal decomposition [23] method have been applied.

Radiation protection is paramount across various sectors such as nuclear energy, diagnostic radiology, and aerospace missions, given the detrimental health impacts linked to ionizing radiation exposure, including acute radiation syndrome and carcinogenesis [24, 25]. In the quest for superior radiation shielding solutions, Gd3+ doped Zn0.5Mg0.5Fe2O4 spinel ferrite nanoparticles have garnered significant interest for their potential in mitigating ionizing radiation risks. These nanoparticles, enhanced with rare earth Gd3+ ions, exhibit exceptional magneto-crystalline anisotropy and magnetic characteristics, positioning them as a promising material for effective radiation attenuation [26,27,28]. Gd3+ doping can modify the properties of Zn0.5Mg0.5Fe2O4 spinel ferrite for specific applications. Its large ionic radius allows it to substitute for Fe3+ ions without distortion. Although not magnetic, Gd3+ can influence magnetic interactions between Fe3+ ions. It can introduce additional functionalities like magnetostrictive or magneto-optical properties. Gd3+ doping affects the lattice parameter, crystallinity, saturation magnetization, coercivity, and band gap of the ferrite. The impact depends on the concentration and synthesis method used. Doping levels should be controlled to achieve desired properties without introducing secondary phases or degrading the material’s performance. The inclusion of Gd3+ ions notably advances the gamma-ray shielding capabilities of Zn0.5Mg0.5Fe2O4 spinel ferrites, offering a path to refine and optimize these materials for critical radiation protection roles. Nanomagnetic materials, like Gd3+ doped Zn0.5Mg0.5Fe2O4, are at the forefront of research for radiation shielding due to their distinctive properties and adaptability, indicating a significant step forward in the development of advanced functional composites for safeguarding against ionizing radiation hazards [29,30,31].

Throughout this work, the Zn0.5Mg0.5Fe2O4 spinel ferrite (ZMF) composite was prepared by the citrate sol-gel auto-combustion method. The structure and its crystalline properties have been examined by using the XRD technique. The surface morphology was obtained by scanning electron microscopy, SEM. HR-TEM analysis was also performed. Fourier transform infrared, FT-IR, spectra were also obtained. RAMAN spectroscopy was adopted to study the internal structure. The X-ray photoelectron, XPS, investigated the binding energy. Also, the structures’ absorption spectra were examined using a UV Spectrophotometer over the range of 340–500 nm. The magnetic properties were investigated using the VSM technique and the dM/dH was calculated. The novelty of this work is conducted throughout the doping of ZMF-spinel ferrite structure by the rare earth element Gd3+ ions at concentration ratios x = 0.025, 0.050, 0.075, and 0.100, respectively. The substitution of Gd3+ ions could strongly evolve further enhanced magneto-optical structure for SFs materials as the net magnetic moment of the rare earth Gd3+ ions, 7.94 μB [32], is larger than its corresponding of other rare-earth cations such as Lu3+ (0 μB) [33], Nd3+ (3.855 μB) [34], Yb3+ (4.63 μB) [35], and Pr3+ (3.4 μB) [36].

This study looks into what happens when Gd3+ ions are added to Zn0.5Mg0.5Fe2O4 spinel ferrite nanoparticles. It focuses on their structure, magneto-optical properties, and ability to block gamma rays. The novelty is that adding Gd3+ to the ZMF4 sample created nano-sized cubic structures with an ideal crystallite size of 19.82 nm. This meant that the electronic properties were better. Magnetic analysis revealed a transition towards superparamagnetic behavior, suggesting potential applications in data storage and optical waveguides. The study also showed that increasing Gd3+ concentration or sample thickness significantly improved radiation attenuation, highlighting the material’s enhanced shielding capabilities against various photon energies. A lot of different advanced techniques were used by the authors, such as XRD, SEM, TEM, FT-IR, Raman spectroscopy, XPS, UV-vis spectroscopy, and VSM measurements, to get a full picture of the shielding properties. We chose the citrate sol-gel auto-combustion method for its precise control of composition and microstructure, which enables the fabrication of nanostructured materials with improved homogeneity and purity. The citrate sol-gel auto-combustion method, used in this study, produces highly homogeneous and fine powders with controlled stoichiometry and particle size. However, it faces challenges in precise control of combustion conditions, which can affect product consistency. The method’s scalability for industrial applications is also a concern due to difficulties in maintaining uniform heating and reaction conditions. Future work should focus on optimizing combustion parameters, exploring alternative synthesis techniques, and investigating the long-term stability and performance of Gd3+-doped Zn0.5Mg0.5Fe2O4 spinel ferrites in practical applications to fully understand their potential and limitations. This work provides a promising path towards the development of advanced functional materials for high-tech applications and radiation protection. Many potential applications could be considered for such enhanced superparamagnetic ZMF-spinel ferrite like Biomedicine [37], Magnetic Resonance Imaging (MRI) [38], Environmental Remediation [39], Data Storage [40], and Energy Harvesting [41].

2 Experimental procedure

ZMF-spinel ferrite composite was successfully prepared by the citrate sol-gel auto-combustion technique. Aqueous solutions of Zn(NO3)2.6H2O, Mg(NO3)2.6H2O Gd(NO3)3.6H2O, and Fe(NO3)3.9H2O were dissolved in deionized water under stirring. Citric acid was weighed as 1:1 (g/mol) molar ratio then dissolved in deionized water under stirring with mild heating. All salts and Citric acid were mixed with continuous, uniform stirring at a 400 r/min rate for 1 h and 80 °C to prepare a homogeneous solution. The gel form was obtained when drops of NH4OH solution were added to the homogeneous solution and then heated at 110 °C for gel combustion while the PH was controlled at around 10. After that, the gel was kept at 110 °C until burnt, and the gray ashes were obtained. These ashes were calcinated at 600 °C for 4 h to obtain Zn0.5Mg0.5Fe2O4 samples. Five samples at different Gd3+ concentrations; x = 0.000, 0.025, 0.050, 0.075, and 0.100, respectively were formed and were denoted as ZMF0, ZMF1, ZMF2, ZMF3 and ZMF4.

3 Samples characterization

Crystallinity and phase structure results of the synthesized SFs were obtained using X-ray diffraction analysis, XRD, Maxima.7000, Shimadzu. The test was performed with the aid of Cu-Kα radiation at wavelength of λ = 1.5418 Å and diffraction angles, 2θ, between 20°–70°. The surface morphology is captured and magnified by scanning electron microscopy, SEM; JEOL, the working conditions include 15 kV high voltage, 5.5 mm distance, 5 nm spot size, and 3000× magnification power. Also, Transmission Electron Microscopy (HR-TEM) is used to study the internal structure and morphology of the ZMF-spinel ferrite samples at very High Resolution, JEOL JEM-2100Plus. The FT-IR (Fourier Transform Infrared) module manufactured by Shimadzu, was used to acquire the infrared spectra. The spectra were collected over the wavenumber range of 250–4000 cm−1. RAMAN spectroscopy was also used to study the internal structure in the range from 25 to 2000 cm−1, Horiba Jobin Yvon LabRAM HR. The binding energy was investigated by X-ray Photoelectron Spectroscopy, XPS, Kratos AXIS Ultra DLD. The absorption spectra of ZMF-spienel ferrites were examined over 340–500 nm using UV/vis/NIR-spectrometer V-570, Jasco Inc. Finally, the magnetic properties were investigated with the aid of Vibrating Sample Magneto, VSM -Lakeshore 7400.

4 Results and discussions

4.1 XRD analysis

The results obtained by the XRD for all ZMF-spinel ferrite samples confirmed the formation of cubic spinel structures according to card number JCPDS #82-1049 [42], Fig. 1a. The preferred oriented peaks at angle 2θ were 29.64°, 34.14°, 34.56°, 54.52°, 60.85°, 65.91° and 67.03° corresponding to the miller indices as (220), (113), (400), (412), (511), (404) and (421) respectively. For more details, Fig. 1b, c represent 25 ≤ 2θo ≥ 40 and 50 ≤ 2θo ≥ 65, respectively, where the vertical dashed lines on each graph show clearly the deviation of the doped samples’ peaks, towards positive x-axis direction. This behavior explains the diffusion of the Gd3+ ions through the structure. The lattice parameters a=b=c (Å) and the crystallite size D (nm) were determined using Scherrer’s equation [43]:

$$D=\frac{k\lambda }{\beta \,\cos \theta }$$
(1)
$${d}_{{hkl}}=\frac{a}{\sqrt{{h}^{2}+{k}^{2}+{l}^{2}}}$$
(2)

Where D is the crystallite size (nm), β is the full width at half maximum, θ is the Bragg’s angle, and d is the interplanar distance of the crystal planes. Table 1 shows the Lattice parameter a (Å), crystallite size D (nm), volume V (Å3), X-ray density (ρx) and Lattice strain (ε) for ZMF-spinel ferrite samples. Figure 1d shows a remarkable increase in the lattice parameter, a (Å), at ZMF1 (x = 0.025) with about 0.01 Å while decreasing for the rest of the concentration ratios. On the other side, the crystallite size D (nm) was found to decrease ≈ 2.11 nm for all ZMF-spinel ferrite samples. The Retiveld XRD refinement for all ZMF-spinel ferrite samples was fulfilled using FullProf software, Fig. 2. Among all structures, ZMF4 sample is claimed to be the optimized one since it possesses smallest crystallite size, 19.82 nm. Concluding that the Gd3+ doping mechanism has primarily enhanced the ZMF-spinel ferrite’s structure would probably modify the other magneto-optical properties of the composite as will be seen in the next sections. The absorption bands observed in our study are indicative of the presence of certain crystalline phases within the material. These bands correspond to specific vibrational modes associated with the crystalline structure of the material. In the case of spinel structures, the characteristic absorption bands can be directly correlated to the distinct atomic arrangements and bonding within the crystal lattice. For example, the bands around 400 cm−1 and 650 cm−1 are typically associated with the stretching and bending vibrations of the M-O bonds (where M represents the metal ions) in spinel oxides. These bands serve as fingerprints for the spinel structure, confirming the successful crystallization into this phase. The agreement between the absorption bands and the XRD data further supports the crystallization into the spinel structure. The absorption bands not only confirm the phase but also give insights into the purity and quality of the crystalline structure. The TEM and SAED analyses complement these findings by providing visual confirmation of the crystalline phases, showing clear lattice fringes and diffraction patterns consistent with spinel structures as we will see in the next section.

Fig. 1
figure 1

XRD for (a) All ZMF-spinel ferrite samples ZMF0, ZMF1, ZMF2, ZMF3 and ZMF4, (b) 25 ≤ 2θo ≥ 40, (c) 50 ≤ 2θo ≥ 65, and (d) lattice parameter a (Å) and crystallite size D (nm)

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Table 1 Lattice parameter a (Å), crystallite size D (nm), volume V (Å3), X-ray density (ρx) and Lattice strain (ε) for ZMF-spinel ferrite samples
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Fig. 2
figure 2

Retiveld Refinement XRD for all ZMF-spinel ferrite samples ZMF0, ZMF1, ZMF2, ZMF3 and ZMF4

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4.2 Morphology

4.2.1 Scanning electron microscopy (SEM) and particle size

The surface morphology and the particle size of the ZMF-spinel ferrite samples were examined using Scanning Electron Microscopy, SEM, Fig. 3. The SEM images showed the particles’ enhancement [44] into spherical-like shape as the Gd3+ ions doping ratio was increased. This enhancement will be explained later in more details in the FT-IR and XPS analysis. Such results show that the optimized combination was obtained for the doped Gd3+ ZMF4 sample. Moreover, the average particles’ diameters were diminishing from 22.3 to 20.5 nm reflecting the presence of the Nano-sized scale for all samples. These results are in consistent with that obtained for the crystallite size determined from XRD.

Fig. 3
figure 3

SEM and particle size distribution images of ZMF-spinel ferrite samples

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4.2.2 HR –TEM and SAED analysis

Figure 4 illustrates the HR-TEM, and SAED micrographs of ZMF-spinel nanoferrites for the pure ZMF0 and the optimized ZMF4 samples. The HR-TEM micrographs have proven the particles’ nano-sized aggregated cubic structure. Such accumulated structure may be customized as a result of larger surface area and magnetic dipole interaction of the constituent ZMF-nanoparticles which increasing with increasing Gd3+ dopant ions [45]. Additionally, such behavior is referenced to the magnetic merit of Gd 3d being lower compared with Fe 3þ ions [46]; as will be explained in the next sections. Moreover, the diffraction rings identified by SAED images are analogous to the peaks (220), (113), (400), and (412) obtained by the XRD; see Fig. 1. These results emphasize the integrity between the HR-TEM and the XRD techniques in confirming the formation of pure cubic spinel phase of Gd 3d doped ZMF-nanoferrites.

Fig. 4
figure 4

HR-TEM and SEAD images of the ZMF0 and ZMF4 samples

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4.3 FT-IR analysis

Figure 5 shows the FT-IR transmittance spectra obtained for ZMF0, ZMF1, ZMF2, ZMF3 and ZMF4 at room temperature in the range of 200–4000 cm−1. The observed representative peaks confirmed the presence of the oxygen-containing functional groups at different Gd3+ ion concentrations of the composite and the characteristic absorption bands were obtained as well. The presence of these bands are mainly due to the vibrations of tetrahedral and octahedral metal–oxygen ions. The pure sample lies in frequency \({{\rm{\nu }}}_{1}\) equal 552.66 cm−1, while the optimized sample ZMF4 lies at \({{\rm{\nu }}}_{1}\), \({{\rm{\nu }}}_{2}\) and \({{\rm{\nu }}}_{{\rm{A}}}\) cm−1 551.14, 381.36 and 836.32, respectively [47, 48]. The first absorption band of the tetrahedral site, lied below 300 cm−1, belongs to the stretching vibration of Zn–O [49], whilst, the second absorption band was confined by the range 440.14–575.68 cm−1 and corresponding to Fe3+–O2− [50] stretching vibrations. The third absorption band lied within the range 1557–1650 cm−1, representing the Mg–O [51]stretching vibrations. Furthermore, the peaks obtained for different concentration ratios within the range 3300–3680 cm−1 which are assigned to O–H [52] deformation and O–H stretching vibrations in H–O–H [53] groups. The results of the FT-IR are presented in Table 2. The positions of the absorption bands were characterized by frequencies shift as the concentration ratio changed due to the cations redistribution and the distortion of crystal resulting from the substitution process [54]. When the Gd3+ ions were doped in the crystal structure, the replacement of Fe3+ by Gd3+ led to decrease in metal-oxygen bonds lengths that caused octahedral sites shifting towards higher frequencies as the Gd3+ ions have larger radii [55].

Fig. 5
figure 5

FT-IR spectra for ZMF0, ZMF1, ZMF2, ZMF3 and ZMF4 spinel ferrite samples

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Table 2 FT-IR absorption band positions for ZMF-spinel ferrite samples
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4.4 RAMAN analysis

RAMAN spectra of ZMF0, ZMF1, ZMF2, ZMF3 and ZMF4 spinel ferrite samples in the range of 25–2000 cm−1 are shown in Fig. 6. The Figure shows different modes at 79.67, 311.56, 663, 1340 and 1580 cm−1 for all doping ratios of Gd3+. The presence of the RAMAN band at 311.56 cm−1 was due to zinc ferrite nanoparticles associated with the α-Fe2O3 phase [56]. The Gd2O3 was synchronized in mode at 663.4 cm−1 [57]. A remarkable increase, high peaks, in RAMAN intensity as the Gd3+ doping ratios increased were found in the range between 1250–1750 cm−1 [58]. The presence of these peaks are attributed to the stretching vibration modes of the Gd2O3. This is a significant result showing the successful doping of Gd3+ ions within the structure which would affect its magneto-optical properties that will be discussed next in Sections 4.6 and 4.7.

Fig. 6
figure 6

RAMAN shift for ZMF0, ZMF1, ZMF2, ZMF3 and ZMF4 spinel ferrite samples

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4.5 X-ray photoelectron spectroscopy (XPS) analysis

The XPS spectra of Zn, Mg, Fe and O elements for ZMF0 and ZMF4 spinel ferrite samples are presented in Fig. 7. The cation distributions at different sites and binding energies obtained for ZMF0 and ZMF4 samples confirmed the presence of Zn(2p3), Mg(1 s), Fe(2p) and O(1 s) peaks, respectively. In the case of the A-site (tetrahedral) and B-site (octahedral) cation distributions, the analyses focus on the elements Zn and Fe. The Zn spectra exhibit two major peaks along with a satellite peak at a higher binding energy (BE) level. The Zn 2p3/2 peak, along with the satellite peak [59], indicate the presence of Zn2+ in the synthesized nanoparticles. The spectra obtained for Mg presented Mg 1 s peak for ZMF0 and ZMF4 confirming the presence of Mg2+ within the structure of the samples. On the other hand, the Fe 2p [60] spectra reveal the Fe 2p3/2 and Fe 2p1/2 peaks at higher (BE) levels. The existence of the Fe 2p3/2 peak suggests the presence of Fe3+ states in the synthesized nanoparticles. A sensitive variation in the binding energy of Fe3+ and Fesat peaks is observed when comparing the spectrum of ZMF4 to that of ZMF0. The spectral peak of O-2 1S1/2 [61] at 529.61 eV for ZMF0 has been shifted to a higher binding energy as the Gd3+ content was increased in the optimized sample ZMF4 to 533.64 eV.

Fig. 7
figure 7

XPS spectra of Zn, Mg, Fe and O elements for ZMF0 and ZMF4 spinel ferrite samples

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In Fig. 8 illustrated XPS spectra of the Gd3+ ions of ZMF1, ZMF2, ZMF3 and ZMF4 spinel ferrite samples. The shifting observed in the deconvoluted Gd 4d3/2 spectra provides compelling evidence that Gd3+ ions has been successfully doped within the synthesized structure where they’ve replaced the Fe3+ ions [62]. These results should affect the magneto-optical properties for the structure which will be discussed in the following sections. The XPS spectra survey of the ZMF0 and ZMF4 samples illustrated the elements Zn, Mg, Fe, C and O very clear, see Fig. 9. The basic spectrum for the pure sample ZMF0 confirmed the presence of Mg 1 s, Zn 2p3, Fe 2p, O 1 s and C 1 s, respectively. The Peaks obtained at around 712 eV and 1022 eV were found to characterized the Fe 2p and the Zn 2p3 electrons, respectively, meanwhile, the peak at 1304 eV was belonging to the Mg 1 s. This is in addition to the peaks observed in the spectrum found at 285, 531 identifying the C 1 s, O1s, respectively. Normally that, the Gd 4d peak is only observed for ZMF4 spectra at about 100 eV. All the XPS results are tabulated in Table 3.

Fig. 8
figure 8

XPS spectra of the Gd3+ ions of ZMF1, ZMF2, ZMF3 and ZMF4 spinel ferrite samples

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Fig. 9
figure 9

XPS Survey of the ZMF0 and ZMF4 samples

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Table 3 XPS results for ZMF-spinel ferrite samples
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4.6 UV spectroscopy analysis

The UV-VIS absorbance, absorption coefficient (α), Extinction coefficient K spectra were plotted as a function of the wavelength. Also, (\({{\rm{\alpha }}{\rm{h}}v)}^{2}\) was plotted against \({\rm{h}}v\) for the ZMF-spinel ferrite samples, Fig. 10a–d. The magnitudes elevations confirm the success doping of Gd3+ ions within the structure since they demonstrated the raise in energy absorbed by electrons offered by the dopant Gd3+ ions.

Fig. 10
figure 10

UV-VIS (a) absorbance, (b) absorption coefficient (α), (c) Extinction coefficient K and (d) (\({{\rm{\alpha }}{\rm{h}}v)}^{2}\) vs. \({\rm{h}}v\) spectra for ZMF0, ZMF1, ZMF2, ZMF3 and ZMF4 spinel ferrite samples

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4.6.1 Absorption coefficient (α)

The spectral results obtained from UV-VIS spectroscopy within 340–500 nm range for the ZMF-spinel ferrite samples were used to calculate the absorption coefficient (α) using Eq. (3)

$$\alpha =-\frac{\mathrm{ln}(1-A)}{\tau }$$
(3)

Where A is the absorbance and \({\boldsymbol{\tau }}\) is the optical length of the samples. According to Fig. 10b, “α” was increasing as the doping Gd3+ ions were raised within the structure of the samples. All samples showed superposed profiles for the intensity of absorbance hovering around 340 nm wavelength. This behavior was dramatically decreased to reach minimum value at 460 nm for all samples. Post 460 nm wavelength, the absorbance rate started to increase forming plateau behavior between 450 nm and 500 nm. The above results reveal that the ZMF-spinel ferrites working wavelength is 300–350 nm range. The Gd3+ ions have modulated the absorption properties of the spinel ferrite structure and the absorption magnitude depends upon the concentration ratio of the rare earth material. The enhancement of the electronic conduction within the structure has improved the electrical conduction of the material and hence approached probable electronic applications in use [63]. High energy photons capable of traveling between the valence and conduction bands could be generated according to the photo-excitation phenomena [64]. As the wavelength increased above 300 nm, the incident photons’ energy became less, resulting in lower probabilities for electrons transitions between bands causing a drop in absorbance magnitude [65]. The maximum absorbance at ZMF4 leads to high ultraviolet photocatalytic [66] effective ability and vice-versa.

4.6.2 Extinction coefficient, k

The variations in the extinction coefficient (k) with respect to the incident light wavelength were calculated for all ZMF-spinel ferrite samples, Fig. 10c, using Eq. (4):

$$k=\frac{\alpha \lambda }{4\pi }$$
(4)

“K” determines the radiation absorption/scatter percentage by the samples at certain wavelength. The values of “K” lie within 300 nm < λ < 500 nm range depending upon the concentration ratios of the Gd3+ within the samples. It is clear that (K) recorded a maximum value at a wavelength of 340 nm.

4.6.3 Optical energy band gap, Eg

The optical band gaps were calculated according to Tauc’s relation represented by Eq. (5). Moreover, the results obtained were plotted between αhν vs. hν in Fig. 10d:

$${\rm{\alpha }}{\rm{h}}{\rm{\nu }}={\rm{A}}{({\rm{h}}{\rm{\nu }}-{\rm{Eg}})}^{{\rm{n}}}$$
(5)

Where A is a constant, h (J.s) is the Planck’s constant, ν (Hz) is the incident light frequency, Eg (eV) is the optical band gap energy and “n” is a power factor that equals to 1/2 for the direct band gap semiconductor materials [67]. The results obtained for the optical band gaps of ZMF-samples were found to decrease from 3.21 eV to 2.99 eV as the doping ratios of the Gd3+ ions were increased, Table 4. The resulting blue shift [68] of the band edge absorption in ZMF-spinel ferrites can be explained following the probabilities of both charge transfer and d-d transitions [69] within the iron (Fe) d-orbitals. A smaller band gap promotes such transitions, potentially leading to bluer light emission. This can be complex and vary depending on Gd+3 ions substitution probabilities. These results are in consistent with those obtained in the previous XPS section.

Table 4 The Energy Gap values for ZMF-spinel ferrite samples
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4.7 Magnetic measurements

The hysteresis loops of the prepared spinel nano-ferrites ZMF0, ZMF1, ZMF2, ZMF3 and ZMF4 at room temperature under the magnetic field in the range of ±20 KOe were shown in Fig. 11. The magnetic parameters including saturation magnetization, Ms, coercivity, Hc and remnant magnetization, Mr obtained from the hysteresis loops are listed in Table 5. In addition, the squareness ratio, Mr/Ms, anisotropy constant, K, and the magnetic moment, μB, were calculated using the following equations and presented in Table 5 as well:

$$K=\frac{{H}_{c}{M}_{s}}{0.96}$$
(6)
$$S=\frac{{M}_{R}}{{M}_{s}}$$
(7)
$${\mu }_{B}=\frac{{MWx}{M}_{s}}{5585}$$
(8)

Where 5585 is the magnetic factor and MW is the molecular weight. It is noticed that the coercivity, HC, values have decreased from 110.95 Oe to 87.69 Oe as the Gd3+ ions were increased. The decrease in HC is interpreted as a consequence of the cation arrangements over the tetrahedral A and octahedral B sites [70]. The magnetocrystalline anisotropy constant (K) is a crucial parameter that describes the dependence of magnetic properties on a material’s crystallographic orientation. It is essential for understanding the magnetic behavior and performance of ferrites, especially when rare earth (RE) elements are introduced. RE elements possess large single-ion anisotropy due to their unpaired 4f electrons, which, when substituted into the octahedral sites of the ferrite lattice, contribute significantly to the overall magnetocrystalline anisotropy of the material, resulting in an increased K. This enhancement enhances the magnetic hardness and stability of the ferrite, making it suitable for high-performance magnetic applications. RE-substituted ferrites exhibit a higher magnetocrystalline anisotropy constant compared to pure ferrites, due to strong spin-orbit coupling and the large orbital contributions of RE ions. In conclusion, RE-substituted ferrites are ideal for high-performance magnetic applications due to their enhanced anisotropic properties. The magnetic order in spinel ferrites is mainly referenced to the superexchange interactions built up among these tetrahedral and octahedral sites through oxygen ions [71]. Rare earth metals have always been recognized as strong paramagnetic in normal temperature conditions [72]. As a result of having larger ionic radii, Gd3+ ions (0.938 Å) become competent to occupy the B sites in trade with smaller Fe3+ ions (0.67 Å). Such trading lead to reduce the total magnetic moment at these sites that yield finally a net reduction in coercivity as the non-magnetic Gd3+ doped ions were increased. Furthermore, MS and Mr were found to decrease from 30.04 to 21.99 and 2.99 to 1.63 for pure sample and ZMF4 respectively. Also, the squareness ratio was found to fall from 99.70 × 10−3 to 67.69 × 10−3 for these two samples as well. All magnitudes drops were noticed to occur as increasing the Gd3+ concentration ratios within the samples. The results obtained for MS is ascribed to the attenuation of the Fe3+– Fe3+ interactions in parallel with the weak Gd3+– Fe3+ and Gd3+– Gd3+ interchanges [72].

Fig. 11
figure 11

The magnetic hysteresis loops (M-H loop) for ZMF0, ZMF1, ZMF2, ZMF3 and ZMF4 spinel ferrite samples

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Table 5 Saturation magnetization (Ms), Remanent magnetization (Mr), Coercivity (Hc), Squareness ratio (Mr/ MS), Effective magnetic anisotropy (Keff) and Bohr magneton (µB)
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The dM/dH curves for ZMF-spinel ferrite samples ZMF0, ZMF1, ZMF2, ZMF3 and ZMF4 are shown in Fig. 12. The width of dM/dH curves was kept constant and overlapped for all of Gd3+ ions doping ratios. Furthermore, the magnitude of the dM/dH peaks were dropped from 0.035 for ZMF0 to about 0.025 for the rest of all doped samples. This behavior is mainly referenced to the presence of the superparamagnetic [73, 74] regions within the structure as the Gd3+ ions concentrations were raised which, in turn, enhanced the magnetic properties of the composite in the direction of soft magnetic. It is noted that the magnetization has improved at higher field of 20 KOe which can be attributed to the superparamagnetic behavior of nanoparticles [75, 76]. Based on the enhanced magnetization status observed in the ZMF-spinel ferrite samples by changing the doping of rare earth Gd3+ratios, several high-tech applications can be envisioned such as transformers, inductors, magnetic recording media, and magnetic sensors.

Fig. 12
figure 12

dM/dH vs. Magnetic Field H (Oe) for ZMF0, ZMF1, ZMF2, ZMF3 and ZMF4 spinel ferrite samples

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4.8 Radiation properties

4.8.1 FLUKA simulation study

In this study, the potent Monte Carlo method called FLUKA (FLUktuierende KAskade) is used to calculate the radiation shielding efficacy of the given nanomaterial. The robust Monte Carlo technique may be helpful in many disciplines due to the expensive costs of laboratory equipment and, of course, the lack of access to it. This code exploits the FLAIR (FLUKA Advanced InteRface) [77,78,79,80] to simplify the editing process, running code, and visualization of the outcomes. This program can simulate the transportation of over sixty particles, including electrons, neutrinos, neutrons, photons, heavy ions, and muons, in wide energy ranges. The FLUKA code version 2011.2x-4 and FLAIR version 2.3 have been used in this work to investigate the radiation shielding efficiency of the selected nanomaterial. In the FLUKA environment, an isotropic spherical photon source spanning from 0.1 to 10 MeV is simulated using BEAM and two BEAMPOS cards. Type: positive, and Type: SPH-VOL with the inner and outer radius of rin = 0, rout = 0.5 cm are selected for the first and second BAMPOS cards, respectively. Additionally, three cm thick lead volumes are simulated around the source and sample. The dimensions of the simulated equipment have been derived from an experimental sample in the reference [81,82,83] that was previously used to test the protection properties of samples. All geometry is encased within BLKBODY shell, with a radius of 13 cm from GEOBEGIN to GEOEND. Ten centimeters away from the photon source, the nanomaterial with a radius of 900 nanometers is simulated. The density of the samples has been entered into the MATERIAL card, and the weight percentages of the material have been added using COMPOUNDS (f1: to f6:) in the FLUKA input file. The simulation system used in this experiment for front and left views are depicted in Fig. 13. Furthermore, spheric volumes are created before and after the sample, and the flux is obtained by applying the USRTRACK (type: linear, part: photon) card. The attenuation factors can be calculated by comparing the initial flux (before the sample) and final flux (after the sample) using Beer Lambert’s Law. The aforementioned cards ensure that the properties and behavior of the simulated nanomaterials closely resemble those of their real-world counterparts, resulting in reliable and relevant radiation shielding predictions.

Fig. 13
figure 13

Front and left views of the simulation study

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To obtain the Cs-137 and Co-60 spectra using FLUKA Monte Carlo code, Hi-PROPE card is used [84, 85]. In this card, the atomic number and mass number of the radioactive source should be added. This card will be used with RADDECAY and DCYSCORE card for each scoring cards and particles. Adding a Semi-analog and kind of the scoring, the gamma photon spectrum can be obtained for each sample. Additionally, USRTRACK scoring cards have been used for wide energy ranging from 0.001 to 1.5 MeV, 100 million primaries, and 5 cycles to minimize errors.

4.8.2 Radiation shielding study

The Ln (Io/I) ratio of the samples at 356 keV is shown against the sample thickness Fig. 14. In the beginning, the ratio is −0.02, which is the largest value. This indicates that all radiation is able to pass through the samples; however, as the thickness of the samples increases, the ratio significantly falls. These samples have a larger thickness, which causes a bigger proportion of the incoming photons to get trapped inside the material, which ultimately results in a greater attenuation. At each and every thickness, the sample that has the maximum amount of Gd has the ratios that are the lowest (more attenuation). To put it another way, increasing the concentration of Gd in the samples means that the Io/I ratio of the samples may be reduced even more at a certain thickness. As a consequence of this, the sample that has the greatest Gd (1 weight percent) also has the lowest Io/I value across all thickness groups.

Fig. 14
figure 14

The Io/I ratio of the samples at 356 keV against the thickness of the samples

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In Fig. 15, the variations in GLAC are shown in relation to the concentration of Gd. This figure serves as a sample example for the lower and higher energy ranges of 0.356–1.333 MeV. The data that has been provided demonstrates that Gd additives have a significant impact on the values of the GLAC, which demonstrate an upward trend in the range of energies that range from 0.356 to 1.333 MeV between the small and high energies. In point of fact, these behaviors may be rationalized by the influence that Gd has on the structural features of samples, such as raising the densities of the samples. The density of a medium has been considered an important factor that plays a role in the medium’s capacity to reduce the amount of radiation photons that it absorbs. It is also important to note that the GLAC is dependent not only on the mass of the photons but also on their energy. To go into further detail, the photon energy had an effect on the rate at which the GLAC altered in response to changes in density.

Fig. 15
figure 15

The linear attenuation coefficient (GLAC) versus Gd content for samples

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For each of the varied Gd concentrations, the GMAC findings for the samples were computed and presented in the form of a photon energies function shown in Fig. 16. For all samples, the GMAC values decrease with increasing the photon energy. In addition, the sample that has 1.0 wt% of Gd has the highest value of GMAC.

Fig. 16
figure 16

The mass attenuation coefficient (GMAC) versus photon energy for samples

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According to the data that are provided in Fig. 17, it is clear that the GHVL values decrease as the concentration of Gd increases from 0 to 1 weight percent within the range of low and high photon energy, which is from 0.356 to 1.333 MeV. One possible explanation for these reductions is that the shielding material densities have an inverse reliance on both GHVL and the shielding material density. It is clear that the GHVL values have decreased as a direct consequence of the rise in density values. In addition, the lower GHVL values indicate that the barrier against nuclear radiation dangers has been increased in effectiveness and efficiency. Based on this discovery, it seems that the presence of Gd has a considerable influence on the shielding capability of the samples that are currently known to exist.

Fig. 17
figure 17

The half value layer (GHVL) versus Gd content for samples

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Furthermore, the nuclear photon build-up factor must be taken into consideration when dealing with nuclear data, such as radiation shielding and dosimetry. The build-up factor is equivalent to the proportion of the target that is contributed by photons that collide with one another. To this investigation, the geometry progressive (G-P) approach was used to ascertain the values of the exposure build-up factor (EBF) and the energy absorption build-up factor (EABF). You may get the specific details on the G-P approach in a publication that was conducted in the past [86]. For this reason, the fluctuation of EBF and EABF with incoming photon energies is shown in Figs. 18a, b and 19a, b, respectively, for samples ZMF0 and ZMF4, with penetration depths of 5, 10, 20, and 40 mfp (as an example). As the input energy declines, the depth-dependent absorption increases until it reaches a maximum value in the intermediate energy field, at which point it decreases. This continues until it achieves a constant value. The majority of gamma-ray absorption takes place in the low (photoelectric dominating) and high (pair formation dominating) energy ranges, which are conditions in which the accumulation of particles is restricted significantly. On the other hand, Compton scattering is the mechanism that is seen the most often for photon-matter interaction at intermediate energies; nevertheless, it is not the mechanism that is observed for absolute photon loss. Therefore, the EBF values are highest in the Compton area as a consequence of this. In addition to the fact that EBF levels vary from area to region, it was discovered that the ZMF4 sample had the lowest EBF values of all the samples that were under investigation. The photon accumulation factor is referred to as the energy absorption build-up factor (EABF), and the quantity of interest is the amount of energy that is absorbed or deposited in the substance of interest. EABF values followed a trend that was comparable to that of EBF values. Tables 6–10 listed the full data of all samples at investigated photon energy range and depth. The research reveals that the incorporation of rare earth elements can significantly improve the structural and magnetic properties of ferrites. This can lead to enhanced magnetic properties, improved structural stability, controlled electrical conductivity, and customized performance for specific applications. The study also reveals that RE elements can be used to enhance magnetostrictive properties for sensors and actuators and improve magnetic permeability for antennas and magnetic recording heads. High-density data storage, transformers, and inductors can use this approach, making ferrites ideal for high-power applications. The findings also suggest that the use of RE resources can promote sustainable synthesis methods, reduce material costs, and promote the sustainable use of resources. The addition of reactive oxygen species (RE) elements to ferrite lattice sites significantly enhances their magnetic properties. This includes altering superexchange interactions, introducing anisotropy, influencing spin alignment, distorting the crystal field, and modifying the magnetic domain structure. This results in increased saturation magnetization and improved magnetic ordering. RE elements also contribute to magnetic anisotropy, resulting in higher coercivity and better stability of the magnetic domains. The pinning of magnetic domain walls also enhances coercivity and overall magnetic hardness, making RE-substituted ferrites ideal for high-performance magnetic applications.

Fig. 18
figure 18

Exposure buildup factor (EBF) versus photon energy at different mean free path of ZMF0 and ZMF4 samples

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Fig. 19
figure 19

Energy absorption buildup factor (EABF) versus photon energy at different mean free path of ZMF0 and ZMF4

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Table 6 (EBF and EABF) G–P fitting coefficients (b, c, a, Xk and d) of ZMF0 sample
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Table 7 (EBF and EABF) G–P fitting coefficients (b, c, a, Xk and d) of ZMF1 sample
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Table 8 (EBF and EABF) G–P fitting coefficients (b, c, a, Xk and d) of ZMF2 sample
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Table 9 (EBF and EABF) G–P fitting coefficients (b, c, a, Xk and d) of ZMF3 sample
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Table 10 (EBF and EABF) G–P fitting coefficients (b, c, a, Xk and d) of ZMF4 sample
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5 Conclusions

This study successfully enhanced ZMF-spinel nanoferrite composites through Gd3+ ion doping, utilizing comprehensive analytical techniques to delve into their structural, optical, and magnetic properties. The introduction of Gd3+ ions notably altered lattice parameters and reduced crystallite sizes to an optimal 19.82 nm, crucially augmenting magneto-optical properties. The nanoscale dimensions were confirmed via SEM and HR-TEM, with SAED analysis corroborating XRD findings through identified diffraction rings. Significant spectral shifts in FT-IR, Raman, and XPS analyses were observed with the optimized ZMF4 sample showcasing distinct peaks and an increase in RAMAN intensity in the 1250–1750 cm1 range as Gd3+ doping ratios were escalated. The research shows that adding Gd3+ ions to Zn0.5Mg0.5Fe2O4 spinel ferrites changed their structure in a big way, creating nano-sized cubic structures with a perfect crystallite size of 19.82 nm. Gd3+ ions, which have a net magnetic moment of 7.94 ¼B, improve the magneto-optical properties, which leads to a change in behavior that is more like a superparamagnetic one. This suggests potential applications in data storage and optical waveguides. The study also assessed the gamma-ray shielding efficiency of these materials, showing that the inclusion of Gd3+ ions significantly improved radiation attenuation. The optimized sample (ZMF4) displayed superior magneto-optical characteristics and outstanding gamma-ray shielding performance, especially at higher Gd3+ levels. When Gd3+ ions were added, the band gap dropped from 3.21 eV to 2.99 eV, which shows that the electronic properties were improved. Gd3+ is not magnetic by itself, but it changes the magnetic interactions between Fe3+ ions, which in turn changes the ferrite’s lattice parameter, crystallinity, saturation magnetization, and coercivity. RE elements for doping face challenges like high costs, environmental impact, complex synthesis, stability issues, and health and safety risks due to their high energy consumption and high energy consumption. A notable shift in the spectral peak of O-2 1S1/2 from 529.61 eV for ZMF0 to 533.64 eV for ZMF4 underscored the impact of Gd3+ incorporation. Optical analyses revealed a band gap narrowing from 3.21 eV to 2.99 eV across the samples, indicative of a blue shift and enhanced electronic properties. Magnetic assessments pointed to a soft magnetic transition and identified superparamagnetic regions, emphasizing the material’s potential across a wide spectrum of technological applications. FLUKA Monte Carlo simulations brought to light the nanomaterial’s improved radiation shielding with increased Gd3+ concentration and sample thickness, showcasing a direct correlation between these factors and photon attenuation efficiency. Samples with 1 wt% Gd exhibited superior shielding, particularly noted in the significant drop in the Ln(Io/I) ratio. Increases in GLAC and GMAC with Gd concentration, especially across photon energies of 0.356 to 1.333 MeV, highlighted the composition’s critical role in shielding effectiveness. Furthermore, the decrease in GHVL with higher Gd levels underscored a denser and more effective radiation barrier. The study’s findings on the exposure and energy absorption build-up factors emphasize the nuanced interplay between photon energy and material interaction, vital for advancing shielding material development. The incorporation of Gd3+ ions into ZMF-spinel ferrites significantly refines their structural, optical, and magnetic characteristics, while also vastly enhancing their gamma-ray shielding capabilities. These improvements suggest the material’s high potential for applications in microwave devices, biomedical fields, energy systems, and notably, in radiation protection, marking a significant leap forward in the development of advanced functional composites and radiation shielding technologies.