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With an aim to explore the d0 ferromagnetism in Ag-doped ZnO compounds, the poly-crystalline samples of Zn 1 - x Ag x O (with 0 ≤ x ≤ 0.12) were synthesized by a standard solid-state synthesis technique. The XRD analyses indicated that these compounds have been formed as Ag:ZnO nanocomposite. According to scanning electron microstructural study, all compounds have a homogenous nearly spherical shape morphology. The EDS spectra reveal that the final produced compounds do not contain any unwanted external impurity. The magnetization versus field measurement at room temperature demonstrates that the undoped ZnO compound shows ferromagnetism embedded in diamagnetic matrix, whereas all Ag-doped ZnO samples exhibit a clear room temperature ferromagnetic behavior with coercivity values between 80 and 196 Oe. The maximum saturation magnetization was obtained for the Zn0.97Ag0.03O sample; however, it declines subsequently. The bound magnetic polarons (BMPs) has been considered to explain the observed ferromagnetic behavior. [ABSTRACT FROM AUTHOR]

Ho3+ion-substituted nanocrystalline cobalt ferrite materials with the chemical formula CoFe2−xHoxO4forx = 0.0, 0.025, 0.05, 0.075 and 0.1 have been synthesised by standard citrate precursor method. Crystal structure and phase purity have been studied by powder X-ray diffraction (XRD) method by employing Rietveld refinement technique. The distribution of cations between the tetrahedral site (A-site) and octahedral site (B-site) has been estimated by Rietveld analysis. The refinement result shows that Ho3+ion has a strong preference for octahedral sites (B-sites). The lattice constants decrease with the Ho3+concentration up tox = 0.05. Crystallite size decreases with the Ho3+concentration. The magnetic hysteresis loop measurements have been carried out at room temperature using a vibrating sample magnetometer (VSM) over a field range of ±2 T. The magnetisations in saturation have been analysed by employing the ‘law of approach (LA)’ technique. The magnetocrystalline anisotropy constant and saturation magnetisation are found to decrease with the Ho3+concentration up tox = 0.05. The coercivity decreases with the Ho3+concentration. The vibrational modes of the octahedral and tetrahedral metal complex in the sample have been carried out using Fourier transform infrared spectroscopy (FT-IR). The FT-IR spectra of the samples have been analysed in the wave number range of 350–1000 cm−1. We have observed two prominent absorption bands which are assigned to tetrahedral and octahedral metal complexes. The elemental analysis has been carried out using energy dispersive spectroscopy (EDS) with the help of field emission scanning electron microscope (FE-SEM) and the results reveal that, elements are as per the stoichiometric ratio in all the samples. [ABSTRACT FROM AUTHOR]

Nanocrystalline TiO2 sample was prepared by high-energy ball mill method. A known quantity of anatase phase-TiO2 was milled for 83 h in air. The samples were collected at intervals of 5 h of milling. The XRD patterns were recorded for all the samples. The crystal structure changed from anatase phase for bulk material to rutile-rich phase for nanocrystalline material. Nanocrystalline TiO2, which is a mixture of anatase, rutile, and srilankite phase, was prepared by milling for 60 h. The XRD pattern of unmilled anatase phase of TiO2 could be refined with I41/amd space group. The crystallite size of the TiO2 was found to decrease with milling time upto 50 h and then the size of rutile phase increases while the sizes of anatase and srilankite phases remain constant upto 60 h of milling. After 60 h, the sizes of all the phases remain constant. The average crystallite size for rutile phase is found to be 12 nm after 60 h of milling. [ABSTRACT FROM AUTHOR]

LaMn1-xCuxO3 compounds have been prepared in single phase form for x - 0 to 0.30. X-ray diffraction patterns recorded at room temperature could be mostly refined using Pbnm space group. Paramagnetic-to-ferromagnetic transitions have been observed up to x = 0.30, from ac susceptibility measurements. Metal-insulator transition in the vicinity of ferromagnetic transition temperature has been observed for x = 0.05 and the resistivity data in the metallic region could be explained in terms of electron-electron and electron-magnon scattering mechanisms. Further increase in Cu-doping beyond x = 0.05 leads to systematic decrease in ferromagnetic transition temperature and ultimately ferromagnetism is destroyed for x = 0.40. The resistivity data of all samples except x = 0.05 exhibit semiconducting behaviors and they could be mostly explained using the adiabatic small polaron hopping model. [ABSTRACT FROM AUTHOR]

We report ferromagnetic behavior in undoped ZnO nanofibers prepared by electrospinning a solution of zinc acetate and poly vinyl alcohol followed by annealing at 550°C for about 90min. X-ray diffraction patterns of the heat treated as-spun composite fibers reveal the formation of ZnO nanowires in wurtzite structure with no noticeable impurity phases. ZnO nanowires annealed between 500°C and 600°C exhibited room temperature ferromagnetism with decreasing magnetization with increasing annealing temperature. Room temperature ferromagnetism was observed in as-spun fibers annealed in air as well as under vacuum. However, vacuum annealed nanofibers show higher magnetization as compared to air annealed fibers, which indicates that oxygen vacancy is a cause for the observed room temperature ferromagnetism in the ZnO nanofibers. [ABSTRACT FROM AUTHOR]

In this study, the tartaric acid modified sol–gel method was used to synthesize (1–x)Bi 0.85 La 0.15 FeO 3 -(x)CoFe 2 O 4 (BLFO-CFO) composites where x = 0.00, 0.10, 0.20, 0.30, 0.40, and 0.50. The X-ray diffraction (XRD) patterns indicated the formation of composites with both BLFO and CFO crystal symmetry, i.e., perovskite and spinel structures, respectively. Rietveld refinement of the XRD patterns was performed for all of the samples in order to analyze the crystal phases and obtain the structural parameters. There were decreases in the lattice parameters of the perovskite phase as the CFO spinel phase increased in the composites, which may be explained by the strain at the interface of the BLFO and CFO phases. Electrical polarization and dielectric constant enhancements were observed in the BLFO-CFO composites compared with BLFO. The saturation magnetization increased as the CFO phase increased in the composites. The theoretical saturation magnetization (calculated using Vegard's law) was less than the experimentally observed value, possibly due to the spin interaction at the interface of BLFO and CFO. [ABSTRACT FROM AUTHOR]

Nanocomposite of NiO and CoFe 2 O 4 (CFO) has been prepared using the high energy planetary ball mill technique. Both crystallographic symmetries correspond to NiO and CFO has been observed from the X-ray diffraction pattern, which indicates no major chemical reaction between the two phases. The fraction of weight percentage for CFO and NiO are obtained from the double phase Rietveld analysis by using the space group F d 3 ¯ m for CFO and F m 3 ¯ m for NiO and, it is found to be as per the expected one. Magnetocrystalline anisotropy has been studied by analyzing magnetic hysteresis loop (obtained in the field range of ±2T) by employing the Law of approach to saturation. The anomaly in the hysteresis loops at symmetric position in the nanocomposite reveals the interaction between antiferromagnetic (NiO) and ferrimagnetic (CFO) phases at the interface. [ABSTRACT FROM AUTHOR]

Abstract: Zn2+ ion substituted nanocrystalline cobalt ferrite materials with the chemical formula CoZn x Fe2− x O4 for x =0.0, 0.1, 0.15, 0.2, 0.25 and 0.3 have been synthesised by standard citrate precursor method. The crystal structure and phase purity have been studied by powder X-ray diffraction (XRD) method by employing Rietveld refinement technique. The cation distribution between the tetrahedral site (A-site) and octahedral site (B-site) has been determined by Rietveld analysis. The distribution of cations changes with the Zn2+ concentration. Average crystallite size and lattice constant increase with the annealing temperature. The lattice constants decrease with the increasing Zn concentration. The vibrational modes of the octahedral and tetrahedral metal complex in the sample have been carried out using Fourier transform infrared spectroscopy (FT-IR). The FT-IR spectra of the sample have been studied in the wave number range of 380–800cm−1 and it shows the presence of absorption bands which are assigned to tetrahedral and octahedral metal complexes. The elemental analysis has been carried out using energy dispersive spectroscopy (EDS) with the help of Field Emission Scanning Electron Microscope (FE-SEM) and the results reveal that the elements are as per the stoichiometric ratio in all the samples. The Magnetic hysteresis loop measurements were carried out at room temperature using a vibrating sample magnetometer (VSM) over a field range of ±2T. Annealing at 200°C, superparamagnetic nature has been observed for compositions x =0.15–0.3. The magnetic data in saturation have been analysed by employing the law of approach (LA) technique. The saturation magnetisation increases with the Zn for x ⩽0.15 and then decreases. The coercivity decreases with the increasing Zn concentration for 600°C annealed samples. The magnetocrystalline anisotropy constants are found to increase for x ⩽0.15 and then decrease with the Zn concentration. [Copyright &y& Elsevier]

In this report, a detail analysis of the impact of annealing temperature on the structural, elastic, morphological, optical, and magnetic behavior of NiFe 2 O 4 nanoparticles prepared by the citrate sol-gel method is presented. Analyzing the XRD patterns by the Rietveld method confirms that all the annealed samples have been crystallized to cubic spinel structure belonging to F d 3 − m space group with a single phase. Rietveld analysis demonstrates the change in structural and microstructural parameters and movement of cations from tetrahedral to octahedral sites and vice-versa upon annealing. The quantitative estimation of Ni2+ & Ni3+ and Fe2+ & Fe3+ has been carried out using XPS analysis. Decreases in peak broadening and shift of five Raman active peaks towards higher frequency upon annealing have been analyzed using the phonon confinement model. The variation in elastic parameters with annealing temperature has been assessed by FTIR analysis. The UV analysis reveals the increase of the optical energy band gap and the decrease of Urbach energy with annealing temperature enhancement. A noticeable sharp absorption band at 748 nm in UV spectra is attributed to A 3 2 g (3 F) → T 3 1 g (3 F) electronic transition. Room temperature magnetic hysteresis loops exhibit an increase of saturation magnetization upon annealing which is discussed with reference to finite size effects and disorderly surface spins. The estimated value of magnetocrystalline anisotropy constant by Law of Approach to saturation (LAS) theory as well as coercivity value elucidates the annealing effect in changing the magnetic single domain state of the particle to a multidomain state. Analysis of ZFC and FC magnetization curve measured at 100 Oe in the temperature range 400 K–60 K reveals the significant impact of annealing temperature on magnetic anisotropy, inter-particle interaction, and blocking temperature. Exploring the magnetic hysteresis loop measured in the temperature range 60–400 K over field strength of ± 3 T demonstrates the significant role of annealing on magnetic exchange interaction. Temperature dependent behavior of saturation magnetization and coercivity has been analyzed using modified Bloch's law and Kneller's relation. The magnetic heating efficiency examined by the induction heating system reveals that the sample has enough potential for hyperthermia application. • Microstructural parameters and Fourier electron density are estimated by Rietveld. • Elastic parameters changes with annealing temperature. • Increase of energy band gap and decrease of Urbach energy occur upon annealing. • ZFC-FC analysis provided information on inter-particle interaction. • SAR is estimated by initial slope, Box-Lucas and modified Newton cooling approach. [ABSTRACT FROM AUTHOR]

Lanthanum (La) modified BFO crystallize to an impurity free crystal structure and enhance the multiferroic properties in BFO. The Bi 0.850 La 0.150 FeO 3 is found to be optimized composition to have very good multiferroic properties. It is also reported that the Ti 4+ substitution significantly reduces the leakage current in BFO. Moreover, the Ti 4+ substitution is more effective than that of magnetic cations to increase the magnetization. Hence, Bi 0.850 La 0.150 Fe 1-x Ti x O 3 (x = 0.000, 0.025, 0.050, 0.100) polycrystalline samples were synthesized by the tartaric acid modified sol gel method and the effect of non-magnetic Ti substitution at the Fe-site of Bi 0.850 La 0.150 FeO 3 on crystal structure and magnetic properties has been studied. The Rietveld refinements of X-ray diffraction patterns indicate the structural transition from rhombohedral ( R3c ) to orthorhombic ( Pbnm ) with the increase in the substitution concentration. A gradual shift in the frequency of Fe-O stretching modes toward higher frequency in the FTIR spectra indicates a composition-driven structural transition. Magnetic properties of Bi 0.850 La 0.150 Fe 1-x Ti x O 3 polycrystalline samples were measured at room temperature with the applied field range of ±7 T. A significant increase in the magnetization with Ti substitution is observed from the magnetic hysteresis loops. The highest magnetic moment was observed for 2.5% Ti substitution at the Fe-site in Bi 0.850 La 0.150 FeO 3 . [ABSTRACT FROM AUTHOR]

The calcium (Ca 2+ ) substituted M-type barium hexaferrite (Ba 1-x Ca x Fe 12 O 19 ) for Ca 2+ (x = 0.00, 0.025, 0.050, 0.075, 0.100, 0.150, and 0.200) have been synthesized by the citrate sol-gel method. The X-ray diffraction (XRD) patterns with Rietveld refinement reveal the formation of hexagonal crystal structure with P6 3 /mmc space group. The lattice parameters a = b and c decrease, whereas lattice strain found to increase with the increase in Ca concentration in the samples. The analysis of Raman spectra well supports the XRD patterns analysis. The average particle size is obtained from the FE-SEM (Field Emission Scanning Electron Microscopy) micrographs and these are similar to that of crystallite size obtained from the XRD pattern analysis. The saturation magnetization and magnetocrystalline anisotropy have been obtained by employing the “Law of Approach (LA) to Saturation magnetization” technique at room temperature. The saturation magnetization and magnetocrystalline anisotropy constant are maximum for 5% Ca substitution in barium hexaferrite. It could be due to lattice strain mediated magnetism. However, these magnetic properties decrease for more than the 5% Ca substitution in barium hexaferrite. It could be due to decrease of magnetic exchange interaction (Fe-O-Fe) in the sample. A correlation between magnetic interaction and lattice strain has been observed in Ca 2+ substituted M-type barium hexaferrite. [ABSTRACT FROM AUTHOR]

Pb1-xSrxZr0.52Ti0.48O3(PSZT) with x = 0–10 mole % were prepared by sol-gel process. X-ray diffraction (XRD) patterns show both rhombohedral and tetragonal crystal symmetries. Increase in lattice strain due to Sr incorporation results in enhanced dielectric constant and piezoelectric co-efficient (d33).With the increase in temperature relaxation time increases from 10−6sec to 10−7sec and spreading factor increases from 0.21 (±0.05) to 0.26 (±0.05) for 10 mole % PSZT. Also, the maximum remanent electric polarization and coercive electric field of 13.64 µC/cm2and 15.97 kV/cm respectively have been observed for 10 mole % samples. [ABSTRACT FROM AUTHOR]

The large electrocaloric effect associated with the ferroelectric-relaxor and ferroelectric-paraelectric phase transition, and various temperature dependent scaling behaviours on A-site modified BaTiO 3 (Ba 1-x Sr x TiO 3 , x = 0.00, 0.10, 0.20, and 0.25) have been reported in this article. The compositionally induced relaxor behaviour with diffuse phase transition has been reported. The Rietveld refinement of XRD patterns reveals that all the samples crystallize to the P4mm space group. Raman spectra analysis at room temperature supports the XRD patterns analysis. The diffuse phase transition behaviour of the prepared sample has been confirmed by estimating the diffuse phase parameter (γ = 1.444 ± 0.003) from the temperature variation dielectric plot. A large adiabatic temperature change (Δ T) of 0.278 K and isothermal entropy change (Δ S) of 0.494 J/kgK have been observed for the sample x = 0.20 (Ba 0.8 Sr 0.2 TiO 3) at 338 K. The temperature dependent scaling relation for remnant polarization (P r), coercive field (E c), and hysteresis area < A > are found to be P r ∝ T − 1.009 , E c ∝ T − 1.890 and < A > ∝ T − 1.169 , respectively. The present comprehensive studies on A-site modified BaTiO 3 illustrate the electrocaloric cooling efficiency of this material. • Significant adiabatic temperature change (Δ T) of 0.278 K on Ba 0.8 Sr 0.2 TiO 3. • Significant isothermal entropy change (Δ S) of 0.494 J/kg K on Ba 0.8 Sr 0.2 TiO 3. • Polar-nano region (Relaxor ferroelectric signature) near the room temperature. • Diffuse phase parameter (γ =1.444) reveals the diffuse phase transition behaviour of Ba 0.8 Sr 0.2 TiO 3. • The scaling relations are P r ∝ T − 1.009 , E c ∝ T − 1.890 , and < A > ∝ T − 1.169 . [ABSTRACT FROM AUTHOR]

Lead Zirconate Titanate [Pb(Zr0.52Ti0.48)O3/PZT] and Cobalt Ferrite [CoFe2O4/CFO] based multiferroic composites [(1-x)PZT-(x)CFO] with (x = 0.10–0.40) have been prepared to study its magnetoelectric (ME) and multiferroic properties. X-ray diffraction method along with the Rietveld refinement technique reveals that the crystal symmetries corresponding to PZT and CFO exist independently in the composites. The effect of interfacial strain on lattice distortion in PZT has been observed. It is well correlated with the magnetoelectric coupling of the composites. Dispersion behavior of dielectric constant with frequency can be explained by the modified Debye model. Different relaxation phenomena have been observed in PZT-CFO particulate composites. The ferroelectric properties of composites decrease with the increase in percentage of CFO in the composite. Both saturation (Ms) and remanent (Mr) magnetization increase with the increase in CFO content in the composite. The maximum ME coupling was found to be 1.339 pC/cm2 Oe for the composition (0.80) PZT-(0.20) CFO at the application of maximum magnetic field of 50 Oe. The multiferroic properties in CFO-PZT can be explained by the lattice strain at the CFO-PZT interfaces. [ABSTRACT FROM AUTHOR]

CoFe 2− x Y x O 4 ( x = 0.0 and 0.05) compound has been synthesized by citrate precursor method and, their structural and magnetic properties have been investigated. X-ray diffraction and Raman spectroscopy have been used to confirm the formation of single phase cubic spinel structure. The X-ray diffraction patterns have been analyzed employing Rietveld refinement technique. The surface morphology and particle size of the samples have been examined using FE-SEM and TEM. Substituting small amount of Y 3+ cation causes significant reduction of the particle size. The magnetic hysteresis curve recorded at room temperature using VSM over a field range of ±2 T shows enhancement in coercivity and reduction in highest magnetization with the Y 3+ substitution. The enhancement of coercivity is attributed to the transition from multidomain to single domain state. The cubic magnetocrystalline anisotropy constants for present samples has been determined by “law of approach” to saturation which suggests the smaller value for substituted sample ( x = 0.05) than that of unsubstituted sample ( x = 0.0). ZFC and FC magnetization measurement over the temperature range 300–900 K shows blocking temperature is far above than room temperature. The decrease of highest magnetization and magnetocrystalline anisotropy constant is ascribed to weakening of superexchange interaction and surface effect. [ABSTRACT FROM AUTHOR]