Ferromagnetic and ferroelectric characteristics of Dy substituted nickel ferrite, NiO Fe1.925 Dy0.075 O3, were investigated. The material formed in the cubic inverse spinel phase with a small amount of DyFeO3 as the additional phase. A small distortion of the cubic lattice was observed upon the substitution of Fe by Dy (in the B site). Substitution of Dy for Fe caused a decrease in the saturation magnetization and Curie temperature of the nickel ferrite. Magnetocapacitance of -4% was observed in NiO Fe1.925 Dy0.075 O3 although the magnetostriction has not significantly changed with Dy substitution. The (high) dielectric constant with frequency is seen to reveal the dispersion in relaxation times. © 2008 The American Physical Society.

Padmam N. Santhosh

Department Of Physics

M. Pattabiraman

G. Markandeyulu

K. Kamala Bharathi

K. Balamurugan

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IIT Madras

Physical Review B - Condensed Matter and Materials Physics

The pure as well as nitrogen incorporated nickel ferrite (NFO and N-NFO) thin films were grown by radio frequency magnetron sputtering technique. The structural investigations of as-grown N-NFO films using GIXRD and Raman spectroscopy revealed nanocrystalline nature of the films. The microstructural and surface studies of the films using SEM and atomic force microscope micrographs showed increase in crystallite size and decrease in surface roughness with increase of sputtering power. The magnetization (M-H) measurements at 20 and 300 K revealed an increase in magnetization and decrease in coercivity values with increase of sputtering power. However, no saturation of magnetization (Ms) was visible for the thin film samples, indicating superparamagnetic behavior due to nanocrystallinity. The comparison of in-plane and out-of-plane magnetizations of the N-NFO film (both at 20 and 300 K) showed that the easy magnetization direction lied in the plane of the film. The optical transmission spectra revealed decrease of direct band gap with increase of sputtering power. © 1965-2012 IEEE.

IEEE Transactions on Magnetics

Magnetic Properties of Nanocrystalline N-NFO Thin Films

In this paper, carbon (C) and nitrogen (N) were incorporated into the interstitial sites of nickel (Ni) ferrite lattice. Structural studies of the incorporated NiFe2O4 (NFO) samples (C-NFO and N-NFO) using X-ray diffraction revealed changes in the values of the lattice parameter, bond angle, and bond length. Raman spectroscopic studies revealed shifts in peak positions of Eg and T2g(3) vibrational modes of the spectra. Magnetization measurements at 20 and 300 K using vibrating sample magnetometer showed decrease in the values of Ms} upon incorporation of C/N (2.3 μB/f.u. of C-NFO and 2.4 μB /f.u. of N-NFO from 2.9 μB/f.u. of NFO, at 20 K). An increase in intrinsic coercive field (Hc) value (18.2 Oe of C-NFO and 14.2 Oe of N-NFO from 5.2 Oe of NFO, at 20 K) was also observed. However, a reduction in the value of first-order cubic magnetocrystalline anisotropy constant (K1) was observed upon incorporation of C/N. Microstructural analysis using scanning electron microscopic images revealed modifications in the shape and the size of the grains. The average grain size was found to be reduced upon C/N incorporation (~600 nm of NFO, while 550 nm of C-NFO and ~400 nm of N-NFO). © 1965-2012 IEEE.

Structure-Property Correlations of Carbon and Nitrogen Incorporated NiFe2O4

We report on structural, spin glass behaviour and competing magnetic interactions in xNiFe2O4 - (1-x)BaTiO3 (x&nbsp;=&nbsp;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&nbsp;K due to the structural transformation of BaTiO3. Magnetization, zero field cooled (ZFC) and field cooled (FC) measurements were carried out from 2&nbsp;K to 320&nbsp;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&nbsp;emu/g with increasing Ni ferrite composition from x&nbsp;=&nbsp;0.2 to x&nbsp;=&nbsp;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&nbsp;=&nbsp;0.3 composition. © 2017 Elsevier B.V.

Journal of Magnetism and Magnetic Materials

Competing magnetic interactions and superparamagnetism like behaviour in xNiFe2O4 - (1-x)BaTiO3 (x = 0.2 and 0.3) nano composites

Spin-polarized density functional calculations, magnetization, and neutron diffraction (ND) measurements are carried out to investigate the magnetic exchange interactions and strong correlation effects in Yb substituted inverse spinel nickel ferrite. In the pristine form, the compound is found to be a mixed insulator under the Zaanen-Sawatzky-Allen classification scheme as it features both charge transfer and Mott insulator mechanisms. Estimation of magnetic exchange couplings reveals that both octahedral-octahedral and octahedral-tetrahedral spin-spin interactions are antiferromagnetic. This is typical of a spin-frustrated triangular lattice with one of the vertices occupied by tetrahedral spins and the remaining two occupied by octahedral spins. However, since the octahedral-tetrahedral interaction is dominant, it leads to a forced parallel alignment of the spins at the octahedral site which is in agreement with the results of ND measurements. The substituent Yb is found to be settled in +3 charge state, as confirmed from the x-ray photoelectron spectroscopy measurements, to behave like a spin-half-impurity carried by the localized fz(x2-y2) orbital. The impurity f spin significantly weakens the antiferromagnetic coupling with the spins at the tetrahedral site, which explains the experimental observation of a decrease in Curie temperature with Yb substitution. © 2017 American Physical Society.

Fulltext

Physical Review B

Effect of frustrated exchange interactions and spin-half-impurity on the electronic structure of strongly correlated NiFe2O4

Temperature dependence of magnetization, anisotropy, and hyperfine interaction parameters of NiFe2-xYbxO4 (x = 0, 0.05, and 0.075) was investigated, and the results are presented. All the compounds were prepared by solid-state reaction formed in cubic inverse spinel phase with the space group Fd\overline 3 m. Increments in the lattice constant were observed upon partial substitution of Fe3+ by Yb3+. Decreased magnetic moment and increased magnetic anisotropy with Yb3+ substitution were observed through magnetization measurements, carried out at 5, 100, 200 and 300 K. Analyses of Mössbauer spectra recorded at 5 K and 300 K, revealed decreased hyperfine fields and magnetic moments at the B-site (and hence net moment) with increasing Yb3+ content. In addition all the compounds exhibited Neel-type, collinear ferrimagnetic structure. © 1965-2012 IEEE.

Journal	Physical Review B - Condensed Matter and Materials Physics
Publisher	APS
ISSN	10980121
Open Access	No