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It remains a challenge to enhance the multiferroic properties of perovskite materials. Herein, we demonstrate a facile sol-gel synthesis of BiFeO3 and Bi0.98Ho0.02Fe1-xCrxO3 (x = 0.01, 0.02, 0.03 and 0.04) nanoparticles with an average size range of 71–35 nm. The crystal phase and structure of as-synthesized powders are studied using Rietveld refinement, which reveal 100% perovskite phase with rhombohedral R3c structure. A saturated loop with small remnant magnetization (Mr) reflects weak ferromagnetism in all the samples. The dc magnetization along with Mossbauer spectroscopy confirms ferromagnetic nature of the compounds. Further, it is to be noted that the co-doping enhances the saturation magnetization to almost three times more than that of pure BiFeO3 and related mechanism was studied in details. Simultaneously, the ferroelectric polarization (Pm) was found to increase from 0.44 μC/cm2 (pure BiFeO3) to 2.08μC/cm2 (Cr doped Bi0.98Ho0.02FeO3). The co-doped samples show high resistivity which is confirmed by the decrease of loss tangent (tanδ) from 3.6 to 0.17 due to the reduction of oxygen vacancies. The band gap of as prepared samples was also found to increase at higher Cr concentration. To the best of our knowledge, for the first time, we have attempted to enhance the multiferroic properties of BiFeO3 using Cr and Ho as co-dopants.

Single phase equi-atomic (Al0.2Co0.2Fe0.2Mn0.2Ni0.2)3O4 high-entropy oxide (HEO) having spinel structure was synthesised employing simple and cost effective microwave assisted co-precipitation technique, followed by calcination at 500 °C. The material obtained was highly crystalline and stable at higher temperatures. The uniformity in elemental distribution was apprehended through STEM-EDS elemental mapping. The X-ray photoelectron spectroscopy confirmed +3 ionic state for Fe and Al, while other elements oxidised to higher ionic states to maintain charge neutrality. Ferrimagnetic behaviour was confirmed for the obtained HEO through magnetic characterisations.

Co-precipitation method was adopted to obtain zinc ferrite nanoparticles substituted with nickel (0.5 ≤ x ≤ 0.7) followed by sintering at 500 °C for 2 h. The formation of spinel ferrite phase in the present ferrite compositions was confirmed from the X-ray diffractograms. The experimental lattice parameter (a) and average crystallite size ( ) are in between 8.359 - 8.348 A and 12.8 – 14.9 nm. As doping level of Ni2+ increases, an interesting relation was existed in between a and , such that the first one is decreasing and the later one is increasing. The variation of average particle size ( ) from FE-SEM is different from the variation of . The present spinel ferrite Ni0.6Zn0.4Fe2O4 possessed smaller particle size of 17.6 nm. The existence of higher and lower vibrational frequencies in between 579–587 cm−1 and 380–386 cm−1, satisfied the Waldron proposals for the ferrite phase. The variations of elastic moduli are very interesting and tricky when compared to the reported literature. The consistency of Poisson’s ratio for these ferrite compositions, revealed the isotropic behavior of present ferrite systems. The saturation magnetization (MS) at room temperature (RT) has uneven variation and a highest value of 43.2 emu/g was noticed for the composition x = 0.6. The coercivity (HC) at RT is gradually increasing with the doping level of Ni2+ ion incorporation. As temperature is decreasing below the room temperature both the MS and HC are increasing for a particular composition. The blocking temperature (TB) lies in the range of 80–125 K and is increasing with the increase of Ni2+ ion concentration. The findings of the present study were discussed in terms of cation distribution and magnetocrystalline anisotropy presuming core-shell morphology.

The inverse spinel lithium ferrite compound LixFe5O8 has attracted a lot of attention because of its highest magnetoelectric coupling temperature. Here, we have investigated the effect of Lithium substitution on the structural and magnetic properties of ordered LixFe5O8−y (x = 0.91 and 1.02) using the X-ray diffraction, Mossbauer spectroscopy, dc magnetization, and neutron diffraction techniques. The Rietveld refinement of X-ray diffraction patterns confirms single phase formation of these compounds in cubic structure (space group P4332). Lithium composition for both compounds was determined using the atomic emission spectrometry (ICP-AES) measurements. The Rietveld refinement of neutron diffraction patterns reveal that both compounds order in a ferrimagnetic structure, where the magnetic moments of iron at the octahedral (12d) and tetrahedral (8c) sites are aligned anti-parallel. The refined values of the ordered moments for Fe3+ ions at 12d (octahedral) and 8c (tetrahedral) sites are 4.185 µB and 4.545 µB, respectively, for x = 0.91; and the corresponding values for x=1.02 are 4.950 µB and 5.274 µB, respectively. An increase in the value of saturation magnetization (in the M vs H study) has been observed with the increasing concentration of the Li. The observed values of the saturation magnetization at 5, 50, 100, 200 and 300 K are 3.91, 3.88, 3.85, 3.76, and 3.51 μB per f.u. for x=0.91 whereas for x=1.02 the corresponding values are 4.76, 4.70, 4.68, 4.56 and 4.33 μB per f.u. The observed increase in the saturation magnetization and ordered moment with increasing the Li concentration has been ascribed to the presence of iron (~9%) at the lithium site (4b) and similar amount of iron vacancies at 12d (octahedral) and 8c (tetrahedral) sites, for the x = 0.91 compound. Our results show that the magnetic properties of these compounds are tunable. The ferrimagnetic order determined using the microscopic neutron diffraction technique in the present study will provide a new pathway to build theoretical models for the magnetoelectric coupling.

M-type hexagonal ferrites with chemical composition Ba0.5Sr0.5CoxAlxFe12−2xO19 (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) have been synthesized by a standard ceramic method. The structural and parameters associated with magnetic properties have been investigated as a function of Co2+ and Al3+ ions substitution in Ba0.5Sr0.5CoxAlxFe12−2xO19 ferrites at room temperature. X-ray diffraction and Fourier transform infrared spectroscopy were used to study the structure of the compositions, and grain morphology was evaluated with scanned electron micrographs (SEM). The Mossbauer studies were performed to investigate the site occupancy and hyperfine interactions in the compositions. The vibrating sample magnetometer was used to record hysteresis loops and magnetic parameters were calculated from hysteresis curves. XRD and FTIR analysis depict the formation of M-type and Spinel phases of the synthesized compositions. SEM images of all compositions show micrometer size structure in the compositions and variation of observed porosity in SEM with substitution is in agreement with calculated porosity from XRD and bulk density. The substitution of Co2+ and Al3+ ions results in reduction of coercivity and saturation magnetization by 76.76% and 38.40% respectively from x = 0.0 to 1.0. The remanent magnetization also observes reduction with substitution. The compositions have good scope for recording and microwave absorber applications.

Nano structured CoCrxFe2-xO4 Ferrites with x = 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0 were prepared through Citrate-gel chemical synthesis. DC electrical resistivity (ρ) of the prepared samples was measured in the temperature range of 200–700 °C using two probe method and room temperature Mossbauer measurements were studied. A decreasing trend ρ with an increase in temperature was observed ensuring the semiconducting nature of the ferrites under test. From the Arrhenius plots (log ρ vs 1000/T), corresponding activation energies for conduction of all the compositions were obtained that show a straight line with two slopes. With an increase in Cr composition, resistivity (ρ) of the ferrite samples was found to increase from 1.4 × 106 Ω-cm to 46.2 × 103 Ω-cm at 300 K. Drift mobility was found to increase with increasing temperature due to a decrease in DC electrical resistivity. Curie temperature (TC) was decreased from 740 K to 641 K and the Activation energy of hopping (ΔE) was increased from 0.075 to 0.222 ev with an increase in Cr composition. This suggests that conduction process in the present Co-Cr nano ferrite system is due to hopping of polarons. The results indicate that the activation energy in the paramagnetic region is higher than that in the ferrimagnetic region. The presence of a paramagnetic doublet in Mossbauer spectra of the samples was attributed to the presence of very small sized nanoparticles in the superparamagnetic regime.

Borosilicate glass is considered to be the standard matrix for immobilization of fission products obtained from the reprocessing of nuclear fuel. However, nuclear waste containing constituents like molybdenum oxide (MoO3) and cesium oxide (Cs2O) are less soluble in borosilicate glass. Hence iron phosphate glass (IPG) is being contemplated as an alternate vitrification matrix since it shows better solubility for these constituents. However, radioactive 137Cs undergoes β− decay to yield 137Ba. In the present work, iron phosphate glass co-loaded with Mo/Cs/Ba ions has been synthesized using the melt quench technique to study their effect on the structure of IPG. The homogeneity, structure and composition of IPG and Mo/Cs/Ba ions co-loaded IPG has been investigated using powder X-ray diffraction, scanning electron microscopy (SEM), electron diffraction spectroscopy (EDS), Mossbauer, FTIR and Raman spectroscopy. A gradual structural modification of the undoped IPG is indicated by the FTIR and Raman spectra with increase in Mo/Cs/Ba ions loading in IPG samples. Detailed thermal analysis of all the glass samples have been done to study their glass stability and glass forming ability which has been estimated in terms of the characteristic temperatures obtained from thermogravimetric analysis (TGA) and differential thermal analysis (DTA) data. The correlation between glass forming ability and the evaluated critical cooling rate of the glasses has been analyzed. Presence of Fe2+ ions has been observed in all the IPG samples as confirmed from Mossbauer spectroscopy. The structure at the atomic scale has been studied in detail using Fe/Mo K-edge X-ray absorption spectroscopy (XAS). The IPG glass co-loaded with Mo/Cs/Ba ions exhibits higher glass transition temperature, comparable glass stability parameters, superior glass forming ability compared to unloaded IPG. Also, a slight modification in the glass structure in Mo/Cs/Ba ions co-loaded IPG as indicated by FTIR, Raman, EXAFS and XANES studies, suggests the potential application of IPG as a suitable vitrification matrix for nuclear wastes having these constituents.

In this work, the synthesis of Ni0.7Zn0.3Fe2-xAlxO4 (x = 0.0–0.6) nanoferrites by combustion method using malic acid as a novel fuel is being reported for the first time. The structural analysis of the nanosized ferrites was carried out by using XRD and IR studies. The cation distribution of all the ferrites was predicted using the Rietveld refinement data and was well supported by the Mossbauer analysis. The XRD parameters were calculated using this predicted cation distribution. The theoretical lattice constant matched exactly with the lattice constant obtained from the Rietveld refinement confirming the predicted cation distribution. The morphology of all the ferrites was studied using the SEM microscopy from which the particle size distribution was calculated along with the EDS mapping which confirmed the presence of all the constituent elements in all the ferrite samples. The dielectric properties of all the ferrites as a function of frequency as well as temperature were studied. The influence of substitution of magnetic Fe3+ by non-magnetic Al3+ in the ferrite series was also studied. It was observed that the addition of non-magnetic Al3+ in ferrites decreases the lattice parameter, density, saturation magnetization, and the Curie temperature. The FC-ZFC magnetization curve revealed a decrease in blocking temperature (TB) with an increase in Al3+ concentration in Ni0.7Zn0.3Fe2-xAlxO4.

The CoCexDyxFe2-2xO4 (x = 0.0, 0.01, 0.02, 0.03, 0.04, 0.05) have been prepared by sol-gel auto-combustion technique. The structural result confirmed the formation of single phase cubic spinel structure showed by XRD. Crystallite size obtained from the XRD is in the range of 24–28 nm, whereas particle size obtained from the transmission electron microscopy is in the range of 20–30 nm. It is also found that the cation distribution of CoCexDyxFe2-2xO4 resulted in the Fe3+ and Co ions occupy both tetrahedral A-site and octahedral B-site, whereas Ce and Dy cation distributed in both of them. The photoluminescence (PL) analysis reveals that all prepared samples contain four bands; (i) peak centered at 412 nm corresponding to ultraviolet (UV) band i.e. near band edge emission, (ii) a high intensity peak centered at 434 nm belonging to violet band, (iii) a low intensity and sharpness peak positioned at 466 nm refers to blue band, and (iv) a broad and very low intensity peak observed at 502 nm assigned to green band. FTIR results of the prepared samples showed that two vibration bands between 600 cm−1 and 400 cm−1 belonging to the stretching vibration of tetrahedral metal-oxygen bond (vA) and stretching vibration of octahedral site (vB) respectively. Mossbauer spectroscopy has also been performed to investigate the hyperfine structure of undoped, Ce and Dy co-doped cobalt nano ferrites. The higher values of MS and Hhf for x = 0.01 composition can be attributed to the occupation of Dy3+ ions in octahedral site whereas the Ce3+ ions occupied to tetrahedral site.

The nanocrystalline Co1−xMnxFe2O4 (0 ≤ x ≤ 0.5) ferrites are synthesized by auto-combustion method. The structural properties and phase identification of the samples are studied using X-ray powder diffraction and the Rietveld analysis. The refinement results confirm that the cationic distribution over the tetrahedral and octahedral sites in the spinel lattice is partially inverse. The magnetic properties of the prepared samples are studied by using an M–H hysteresis curves. The maximum saturation magnetization and coercivity of samples are 68.94 emu/gm and 1.59 KOe respectively. From 57Fe Mossbauer spectroscopy data, the variation in line width, isomer shift, quadrupole splitting and hyperfine magnetic field on Mn2+ substitution have been studied. The composition dependent cation distribution estimated from Rietveld analysis and magnetic studies is in good agreement with each other.

Herein, we report the synthesis of Co–Zr doped BaCoxZrxFe(12−2x)O19 (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) M-type hexagonal ferrites under sol–gel (series 1) and citrate precursor sol–gel (series 2) conditions. These compounds were characterized by TG-DTA, FT-IR, XRD, EDS and BET techniques. XRD patterns and parameters reflect that series 2 yield more symmetrical structures with lower average particle size. Results reveal that magnetization and magnetocrystalline anisotropy are closely related to the distribution of Co–Zr on the five sub lattices. The compounds of series 1 register a steep fall in coercivity [5428 Oe (x = 0) to 630.2 Oe (x = 1.0) than series 2 [2790 Oe (x = 0) to 1210 Oe (x = 1.0)]. MS varies from 63.63 to 56.94 emu/g and 62.79–53.78 emu/g in series 1 and 2, respectively. Mossbauer analysis suggests that site preferences strongly depend upon the nature of dopant, fuel and the preparatory conditions.

We have reported the effect of Cr 3+ ion doping on the structural, ac transport and Mossbauer spectral studies of ferrite nanoparticles Ni 0.5 Mg 0.5 Fe 2 − x Cr x O 4 ( x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) prepared by sol–gel auto combustion technique. The micro-structural studies of the samples were obtained by using scanning electron microscopy (SEM). The dependence of Mossbauer parameters, viz., line width, isomer shift, quadrupole splitting and hyperfine magnetic field on Cr 3+ substitution have been analysed. Hyperfine magnetic field and isomer shift values decreases whereas line width increases with Cr 3+ substitution. Rietveld refinement and Mossbauer spectroscopy studies reveal that the Ni 0.5 Mg 0.5 Fe 2 − x Cr x O 4 with various concentrations of x belongs to mixed spinel structure. Neel’s molecular field model is used to explain the variation of hyperfine magnetic field with increasing Cr 3+ substitution.

The present study deals with the preparation and hydrogen absorption studies on Ti 0.67 Nb 0.33− x Fe x ( x = 0.00, 0.13, 0.20) alloys. From X-ray diffraction results it is inferred that the three alloys are bcc phase and get converted to fcc phase upon hydrogenation. Ti 0.67 Nb 0.13 Fe 0.20 alloy showed maximum hydrogen storage capacity (2.62 wt%) with fastest kinetics among the studied compositions. The hydrogenation kinetics of Ti 0.67 Nb 0.13 Fe 0.20 alloy was studied in detail over the temperature range from 298 K to 473 K. Two different types of rate equations were required to fit the kinetic data, indicating two different rate determining steps (rds) during the progress of hydriding reaction. The activation energies for the two rate determining steps have been calculated from hydrogen absorption kinetics study at different temperatures. 57 Fe Mossbauer spectroscopic study of Fe substituted alloys and their corresponding hydrides show the effect of hydrogenation on the electronic structure of the alloys in terms of electronic charge distribution and volume expansion.

Nanoparticles with compositions of Cu0.4−0.5xCd0.2Ni0.4+xFe2−0.5xO4 (0.0 ⩽ x ⩽ 0.5) were successfully synthesized by a citrate–nitrate sol–gel auto combustion route. The combusted powder was calcinated at four hours in a furnace and then slowly cooled to room temperature. The analysis methods of FTIR, XRD, FESEM, VSM and dielectric measurements were used to characterize prepared magnetic particles. The effect of Ni2+ substitution on structural, magnetic and dielectric properties of Cu–Cd ferrite nanoparticles was studied. The comprehensive studies on compositional and frequency dependent dielectric properties were carried out by means of AC conductivity (σac), imaginary dielectric constant (e′′), loss tangent (tan δ), impedance and dielectric modulus (real and imaginary) measurements in frequency range of 50 Hz–5 MHz at room temperature. The structural properties investigated by using X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy. X-ray diffraction pattern and FTIR results revealed that synthesized samples are in single phase. It is observed that the dielectric constant (e′′) and dielectric loss (tan δ) value decreases with increase in Ni2+ concentration (x). At low frequency the Maxwell type interfacial polarization was observed. Magnetization measurement shows that the Curie temperature of the samples increases with Ni2+ concentration, which is explained by a change in the A–O–B super exchange interaction.

Superparamagnetic properties of the cobalt ferrite nanocrystals have been demonstrated. The significance of the solgel autocombustion method in preparation of cobalt ferrite oxide in the nano range (30–40 nm) has been very well complimented with the structural, dimensional and morphological techniques, such as X-ray diffraction technique, Transmission Electron Microscopy and Scanning Electron Microscopy. The valence states of the metal ions and single phase formation of the polycrystalline oxide have been confirmed with the help of X-ray photoelectron spectroscopy and Raman spectroscopy. The distribution of the Fe3+ ions in the tetrahedral and octahedral lattice sites has been illustrated with the help of the Mossbauer spectroscopy that shows five sextets, indicating occupancies of one tetrahedral and four octahedral sites by Fe3+ ions. Hyperfine fields of 51.29, 48.74, 46.78, 43.58 and 48.59 Tesla, respectively in CoFe2O4 have been found for four octahedral and one tetrahedral site respectively, at ambient temperature. The magnetic measurements M–H and M–T demonstrate a change in the magnetic moment and a superparamagnetic–ferrimagnetic transition at 235 K in the ferrite system.

Mn 0.3 Ni 0.3 Zn 0.4 Fe 2 O 4 ferrite nanoparticles were synthesized by thermally initiated autocatalytic decomposition of metal fumarato-hydrazinate complex. The chemical phase analysis has been carried out by X-ray powder diffraction method. The formation of complete ferrite phase occurred when the sample was annealed at 1100 °C. The physical properties such as lattice parameter, bulk density and porosity were studied. The infra red spectra displayed two bands characteristics of spinel ferrite due to M–O stretching vibrations in tetrahedral and octahedral sites. The X-ray photoelectron and Mossbauer spectroscopy were used to study the valence and distribution of cations in tetrahedral (A) and octahedral [B] sites of the spinel. The frequency dependence of the dielectric properties such as dielectric constant, e ′, complex dielectric constant, e ″ and dielectric loss factor, tan δ , were studied at variable temperatures and reported in this paper.