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The synthesis of a novel multicomponent perovskite was carried out by substituting 5 cations in the A-site of BaTiO3 lattice. The mechanochemical synthesis involved 5 h of ball milling followed by annealing at 800 °C for 2 h and the compound was sintered at 1200 °C for 2 h to form the cubic perovskite phase adopting the P m 3 ¯ m space group. The lattice parameter was found to be 0.391 nm. The reduction in the tetragonality and the local distortion in the compound were observed in the 2D charge distribution maps. The band gap of the compound was found to be 2.94 eV with a dielectric constant value of 270. Ferroelectric hysteresis loops were recorded and the leakage current density was found to be in the order of 10−5 A/cm2.

The effect of Al addition to CoFeMnNi on the phase evolution and magnetic properties was studied for vacuum arc-melted AlxCoFeMnNi (x = 0, 0.3, 0.7, 1) alloys. These alloys were subsequently homogenized at 1050° C for 50 h and water quenched. The CoFeMnNi and Al0.3CoFeMnNi alloys showed single-phase FCC in as-cast and homogenized conditions. The Al0.7CoFeMnNi alloy showed BCC + FCC phases in as-cast condition, and the phase fraction of FCC phase increased upon homogenization. The AlCoFeMnNi alloy had B2 phase in as-cast condition and had BCC + FCC phases after homogenization. Scheil simulation was performed to predict the phase evolution during casting, and calculation of phase diagram (Calphad) approach was used to predict the phase evolution during homogenization. CoFeMnNi alloy was ferromagnetic in as-cast condition, whereas it exhibits spin or cluster glass behaviour after homogenization. The Al0.3CoFeMnNi alloy remained paramagnetic in both as-cast and homogenized condition. In Al0.7CoFeMnNi alloy, the saturation magnetization increased from 20 to 60 emu/g upon homogenization. In the as-cast alloys, AlCoFeMnNi had a maximum saturation magnetization of 126.2 emu/g, and upon homogenization, the saturation magnetization decreased to 94.3 emu/g due to the phase change associated with it. The BCC/B2 phase with equiatomic or near-equiatomic composition had a high saturation magnetization. The change in magnetic properties is correlated to the phase change associated with Al addition and homogenization.

Entropy stabilization was attempted through the addition of 5 different rare earth cations, 5 different transition metal cations and all these 10 cations in the form of three compounds based on NiFe2O4. Equiatomic ratios of these cations were used to maximize the entropy stabilization effect. The compounds attempted and investigated were NiFe1.9(Dy0.02Er0.02Gd0.02Ho0.02Tb0.02)O4, (Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)Fe2O4 and (Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)Fe1.9(Dy0.02Er0.02Gd0.02Ho0.02Tb0.02)O4. Synthesis of these compounds were carried out by sol–gel technique and all the compounds were found to crystallize in F d 3 ¯ m spinel structure indicating the entropy stabilization. An appropriate calculation of configurational entropy of mixing employing the sublattice model is demonstrated for such entropy stabilized oxides.

We report on the effect of α-Fe₂O₃ phase in the magnetic properties and magnetic interactions in nickel ferrite (NiFe₂O₄-NFO) nanoparticles synthesized by co-precipitation method. Structural analysis confirms the formation of the cubic inverse spinel phase without any impurities for the NFO sample annealed in air at 650 °C. When the annealing temperature is increased to 750 °C and 850 °C, α-Fe₂O₃ impurity phase is formed along with the parent NFO phase. Raman spectra recorded at room temperature (RT) confirm the presence of pure NFO phase for the sample annealed at 650 °C, and presence of α-Fe₂O₃ phase is observed in the samples annealed at 750 °C and 850 °C. Saturation magnetization values at RT for the NFO samples annealed at 650 °C, 750 °C and 850 °C are 34 emu/g, 19 emu/g and 28 emu/g respectively. Zero Field Cooled (ZFC) and Field Cooled (FC) measurement reveals the super-paramagnetic behavior along with competing magnetic interactions in all the samples. For the NFO sample annealed at 750 °C and 850 °C, a drop in ZFC magnetization and a small kink in FC magnetization observed around 245 K indicate the presence of a Morin transition (TM) from the α-Fe₂O₃ phase. Anisotropy constants were calculated for all the samples using the law of approach to saturation (LAS) method. The magnetocrystalline anisotropy energy distribution function for the NFO samples annealed at 750 °C and 850 °C exhibit broad peak due to the random distribution of spins associated with different particle size.

We report on magnetocapacitance, spin dynamics through AC succeptability measurements and dielectric anomalies in 0.3NiFe2O4 – 0.7BiFeO3 nanocomposite. Structural studies (purity and phase) and surface morphology of the 0.3NiFe2O4 – 0.7BiFeO3 nanocomposite were examined by X-ray diffraction (XRD), Raman Spectra, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). TEM and SEM images indicate the uniform distribution of nanoparticles in parent pahase as well as in the composite. Energy dispersive X-ray (EDX) analysis indicates the presence of Ni, Fe, O and Bi elements in 0.3NiFe2O4 – 0.7BiFeO3 nanocomposite. Magnetization measurements were performed at 300 K, 50 K and at 2 K and the Field Cooled (FC) and Zero Field Cooled (ZFC) measurements were carried out from 350 K to 2 K. ZFC and FC magnetization curves exhibit a hump around 30 K indicating the existence of competing magnetic interactions and possible spin galss behaviour. AC succeptibility measurements at various frequencies confirm the spin glass freezing behaviour of 0.3NiFe2O4 – 0.7BiFeO3 nanocomposite around 25 K with the relaxation time and activation energy in the order of 10−7 s and 0.938 meV respectively. The dielectric constant and dielectric loss at various frequencies and temperatures indicate the dielectric relaxation behaviour of 0.3NiFe2O4 – 0.7BiFeO3 nanocomposite. A rapid increase in the dielectric constant near the antiferromagnetic transition temperature (TN ∼ 643 K) of BiFeO3 indicates the existence of magneto-electric coupling in this composite. Magnetocapacitance (MC) of 0.3NiFe2O4 – 0.7BiFeO3 composite was measured at room temperature and the MC values of 13.5% and 7.8% (at 5000 Oe) are observed when the pellet is perpendicular and parallel to the magneticfield direction respectively. The presented magnetic and dielectric studies reveal the existence of magnetoelectric coupling and spin glass frezing of 0.3NiFe2O4 – 0.7BiFeO3 nanocomposite.

We report on dielectric anomalies, competing magnetic interactions and relaxor ferroelectric behaviors of xPMN–PT–(1 – x)NiFe2O4 (x = 0.2 and 0.4) nanocomposites. The crystal structure and surface morphology of the pure and composite nanomaterials were examined by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Phase formation and purity of the NiFe2O4, PMN–PT and the composites were confirmed from XRD measurements. Uniformly distributed nanoparticles and nanowires and the presence of Ni, Fe, O, Pb, Nb, Mg, and Ti in NiFe2O4 and PMN–PT are confirmed from FESEM and energy dispersive X-ray (EDX) measurements. Structural disordering due to phase transition around 453 K in both composites was examined from temperature variation Raman studies. Magnetization measurements at room temperature and at 40 K, zero field cooled (ZFC) and field cooled (FC) magnetization measurements for both composites were carried out from 2 to 350 K. Competing magnetic interacti...

We report on structural, spin glass behaviour and competing magnetic interactions in xNiFe2O4 - (1-x)BaTiO3 (x = 0.2 and 0.3) nanocomposites prepared by sol-gel method. The structure and surface morphology of the NiFe2O4-BaTiO3 composites were examined by X-ray diffraction (XRD) and scanning electron microscope (SEM). XRD measurements of composite materials show the presence of both NiFe2O4 and BaTiO3 phases. FESEM and energy dispersive X-ray (EDX) measurements indicate uniformly distributed nano size particles and presence of Ni, Fe, O, Ba and Ti elements respectively. Temperature variation Raman spectra indicates large structural disordering (Peak broadening and shift) around 395 K due to the structural transformation of BaTiO3. Magnetization, zero field cooled (ZFC) and field cooled (FC) measurements were carried out from 2 K to 320 K for both composites. ZFC and FC measurements reveal the spin glass and Superparamagnetism like behaviour along with competing magnetic interaction in both composites. Saturation magnetization value is seen to increase from 6.7 to 10 emu/g with increasing Ni ferrite composition from x = 0.2 to x = 0.3. Distribution function associated with magnetocrystalline anisotropy energy barrier exhibits broad peaks due to the random distribution of spins associated with different particle size in the x = 0.3 composition.

We report on the effect of α-Fe₂O₃ phase in the magnetic properties and magnetic interactions in nickel ferrite (NiFe₂O₄-NFO) nanoparticles synthesized by co-precipitation method. Structural analysis confirms the formation of the cubic inverse spinel phase without any impurities for the NFO sample annealed in air at 650 °C. When the annealing temperature is increased to 750 °C and 850 °C, α-Fe₂O₃ impurity phase is formed along with the parent NFO phase. Raman spectra recorded at room temperature (RT) confirm the presence of pure NFO phase for the sample annealed at 650 °C, and presence of α-Fe₂O₃ phase is observed in the samples annealed at 750 °C and 850 °C. Saturation magnetization values at RT for the NFO samples annealed at 650 °C, 750 °C and 850 °C are 34 emu/g, 19 emu/g and 28 emu/g respectively. Zero Field Cooled (ZFC) and Field Cooled (FC) measurement reveals the super-paramagnetic behavior along with competing magnetic interactions in all the samples. For the NFO sample annealed at 750 °C and 850 °C, a drop in ZFC magnetization and a small kink in FC magnetization observed around 245 K indicate the presence of a Morin transition (TM) from the α-Fe₂O₃ phase. Anisotropy constants were calculated for all the samples using the law of approach to saturation (LAS) method. The magnetocrystalline anisotropy energy distribution function for the NFO samples annealed at 750 °C and 850 °C exhibit broad peak due to the random distribution of spins associated with different particle size.

A series of novel mixed oxides with honeycomb layered structure viz. delafossite-type Na3M2SbO6 (where M = Cu; Ni; Cu, Ni; Cu, Ni, Co; Cu, Ni Co, Fe; Cu, Ni Co, Fe, Mn) were synthesized by a facile method. The synthesis involved heating of the metal precursors at 1100 °C followed by air quenching. The structure was analogous to that of Na3Ni2SbO6 (space group: C2/m). The effect of increased entropy on the Jahn-Teller distortion effect, as previously reported in M = Cu system, was evident from the X-ray diffraction (XRD)/Rietveld structural analysis. The as-synthesized oxides showed photocatalytic activity as confirmed by the degradation of methylene blue. This was correlated to a drop in the optical band-gap from 2.41 to 1.96 eV on increasing the number of elements as well as its effect on the band energies are proposed here.

We report the effect of substitution of 10% divalent ion (Mn2+, Co2+ and Ni2+) on the magnetization of Zn ferrite thin films. M0.1Zn0.9Fe2O4 (M = Mn2+, Co2+ and Ni2+) thin films were pulse laser deposited on to fused quartz substrate at substrate temperatures (TS) ranging from room temperature (RT) to 750 °C. Some of the films deposited with substrate at room temperature were also annealed at different temperatures (TA). While the bulk samples of similar composition are paramagnetic at room temperature, the films were found to be magnetically ordered. The values of magnetization obtained were dependent on TS and TA, similar to pure Zn ferrite films. However, the magnetization values for substituted films were stable over a much larger range of substrate temperatures than pure Zn ferrite films. The thin films of Co0.1Zn0.9Fe2O4, Mn0.1Zn0.9Fe2O4 and Ni0.1Zn0.9Fe2O4 deposited at TS = 750 °C showed the 10 K magnetization values of 5.8 kG, 4.4 kG and 4.5 kG respectively and 0.1 kG, 0.3 kG and 0.2 kG at RT respectively. These values are to be compared with the reported values of ZnFe2O4 thin films deposited at TS = 750 °C, which showed magnetization value of 0.7 kG and 0.2 kG at 10 K and RT respectively. The magnetic properties of bulk and thin films of M0.1Zn0.9Fe2O4 were explained based on the cation occupancy of A and B-sites.

Composites of NiFe2O4 (NFO)–BaTiO3 (BTO) and NiGd0.01Fe1.99O4 (G0.01)–BTO were investigated by x-ray diffraction, magnetization, transmission electron microscopy, magnetocapacitance, and ferroelectric studies. NFO and G0.01 nanoparticles were synthesized by the sol-gel method. The crystallite size of the nanoparticles estimated from the x-ray diffraction patterns is 20–22 nm. The average crystallite sizes of NFO and G0.01 nanoparticles were estimated from the transmission electron micrographs as 26 (1) nm and 22.3 (0.3) nm, respectively. These nanoparticles were encapsulated in a BTO shell, resulting in the formation of nanocomposites. Room temperature magnetization (at 60 kOe) of G0.01 nanoparticles was found to be slightly higher than that of NFO nanoparticles, due to the larger moment of Gd3+ than that of Fe3+. Also, the magnetization of G0.01–BTO is more than that of NFO–BTO nanocomposites. The magnetoelectric effect was observed with a magnetocapacitance value of approximately −10% at 10 kHz in both the composites.

We report on temperature dependent magnetization and anisotropy properties, magnetic interactions at low temperatures, high temperature magnetic properties and frequency dependent dielectric properties of 0.3NiFe2O4–0.7Na0.5Bi0.5TiO3 nanocomposites. X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) techniques are employed to study the crystal structure, morphology and the chemical state of the NiFe2O4 (NFO) nanoparticles, Na0.5Bi0.5TiO3 (NBTO) nanorods and nanocomposites. XRD and Raman spectroscopy studies indicate the formation of NFO, NBTO and the nanocomposites in pure phase. SEM and TEM images indicates the presence of both nanoparticles (from NFO) and nanorods (from NBTO) in the 0.3NiFe2O4–0.7Na0.5Bi0.5TiO3 nanocomposites and the lattice planes with respect to both the phases are confirmed from the selected area diffraction pattern. Magnetization measurements at various temperatures (300 K, 40 K, 10 K and 2 K), field cooled (FC) and zero field cooled (ZFC) magnetization from 300 K to 2 K are measured for the nanocomposites. Saturation magnetization value at 300 K and 2 K for the nanocomposites is seen to be 14.62 emu/g and 16.80 emu/g respectively. Existence of spin glass behavior and competing magnetic interactions in the 0.3NiFe2O4–0.7Na0.5Bi0.5TiO3 nanocomposites is confirmed from the ZFC and FC magnetization studies. Curie temperature value for 0.3NiFe2O4–0.7Na0.5Bi0.5TiO3 nanocomposites is observed to be 900 K. Frequency dependent dielectric studies shows the relaxation behavior of the nanocomposites with two relaxation times of 5.803 × 10−2 s and 2.770 × 10−4 s arising from NFO and NBTO phases.