Markayendeyulu G

Magnetoimpedance (MI) effect was studied on amorphous Co33Fe33Ni7Si7B20 ribbons that were irradiated with N+1, Ar+2 and Xe+5 ions, at energy of 75 keV. The (MI)m [maximum MI in each case] values are 9.4% and 11%, 9.9% and 6.5%, the largest, for the as-quenched and N+1, Ar+2 and Xe+5 ion irradiated ribbons respectively, at 2 MHz. The (MI)m value of the N+1 ion irradiated ribbon was observed to be the highest, due to an induced in-plane transverse magnetic anisotropy. The saturation magnetizations of the ion-irradiated ribbons are not seen to change with respect to that of the as-quenched ribbon; a small increase in the Ms was observed only upon irradiation with Xe5+ ions. The interaction between the large number of domains, with large uniaxial anisotropy led to large (MI)m values, at frequencies above 8 MHz in the Ar+2 ion irradiated ribbon.

The influence of addition of Co on the structural and magnetic properties of MnSb was investigated. The compound formed in the NiAs-type hexagonal structure. Addition of Co to MnSb causes changes in both the lattice parameters. It was observed, from magnetization measurements, that both Curie temperature and saturation magnetization decrease from those of MnSb. The spin-polarized density of states (DOS) calculations revealed that the intermetallic compound favors ferromagnetic ground state even after as much as 0.25 atom of Co per formula unit of MnSb. Charge transfer takes place from the interstitial Co-atom to minority spin band of Mn-atom resulting in an increase in the DOS compared to MnSb at the Fermi level. MnSbCo0.25 exhibits a negative magnetocaloric effect with the largest change in the entropy value, ΔSm = 2.5 J. kg-1. K-1 (for a change in magnetic field from 0 to 5 T), across the second order phase transition at 292 K. The change in the value of magnetic entropy is low around the phase transition and might be due to the small magnetic moment of Mn-atom.

Structure and magnetostriction of Tbx Dy0.9-x Nd 0.1 Fe1.93 (0.2

The structural and dielectric characteristics of NiFe1.925R0.075O4 (R=Lu,Y) were investigated. The material crystallize in the cubic inverse spinel phase with a very small amount of RFeO3 (R=Lu,Y) as the additional phase. Frequency variation of the dielectric constant shows the dispersion that can be modeled with a modified Debye's function, which considers the possibility of more than one ion, contributing to the relaxation. Impedance spectroscopic analysis indicates the different relaxation mechanisms, bulk grain and grain-boundary contributions to the electrical conductivity and capacitance of these materials. © 2014 AIP Publishing LLC.

Ribbons of Fe73.5Si13.5B8CuV 3-xAlNbx (x 0, 1.0, 1.5) alloys were prepared by melt-spun technique at the speed of 37 m/s. Crystalline phase derived from Fe 3Si, in an amorphous matrix was observed in all the ribbons. As cast nanocrystalline ribbons were obtained by controlling cooling rates while quenching. The average crystallite sizes was calculated using the Scherrers equation to be 44 nm, 39 nm, and 35 nm in x 0, x 1.0, and x 1.5 ribbons, respectively. Magnetoimpedance measurements were carried out using an LCR meter. Among the investigated samples (x 0, 1.0, 1.5), the largest magnetoimpedance of 61 was obtained for x 1 ribbon annealed at 100 °C for 15 min, at 4 MHz. © 2013 American Institute of Physics.

Sm- and Ho-substituted and pure nickel ferrite materials, namely, NiFe 1.925Sm0.075O4, NiFe1.925Ho 0.075O4, and NiFe2O4, have been synthesized by the solid-state chemical reaction, and their structural, magnetic, dc electrical conductivity, ferromagnetic, ferroelectric, and dielectric properties have been evaluated. Sm- and Ho-substituted nickel ferrites crystallize in the cubic inverse spinel phase with a very small amount of SmFeO3 and HoFeO3 as the additional phase, respectively. X-ray diffraction studies indicate rhombohedral distortion in NiFe1.925Sm0.075O4 and NiFe 1.925Ho0.075O4 compounds. The existence of ferroelectricity in NiFe1.925Sm0.075O4 and NiFe1.925Ho0.075O4 has been confirmed from the ferroelectric loops, and the respective transition temperatures are 543 and 677 K. The respective magnetocapacitance values are -1.8% and -1.2%. Magnetoelectric coefficients observed at 500 Oe in the NiFe1.925Sm 0.075O4 and NiFe1.925Ho0.075O 4 compounds are 1.82 and 1.84 mV cm-1 Oe-1, respectively. A considerable increase in the saturation magnetostriction value has been observed upon the substitution of Sm. Substitution of Sm and Ho for Fe at the B site increases the dielectric constant compared to that of pure nickel ferrite. Frequency variation of the dielectric constant shows a dispersion that can be modeled with a modified Debye function, which considers the possibility of more than one ion contributing to the relaxation. Electrical conductivity curves confirm the improved resistivity of the NiFe1.925Sm 0.075O4 and NiFe1.925Ho0.075O 4 compounds compared to that of pure nickel ferrite. Analysis of the temperature-dependent conductivity indicates that the small polaron and variable-range-hopping mechanisms are operative in the 220-300 and 160-220 K temperature regions, respectively. © 2010 American Chemical Society.

The giant magnetoimpedance (GMI) effect in amorphous and nanocrystalline Fe73.5Si13.5B8CuV3Al ribbons has been studied as a function of a dc magnetic field, by contact and non-contact methods. In the contact method, an MI of 19% was obtained in the nanocrystalline ribbon while it is of the order of 104 in the non-contact method. The huge sensitivity of the non-contact method is promising with regard to the increase of the sensitivity of the MI sensors. Field dependence of MI has shown double peak behavior in contact method and single peak profile in non-contact method. The domains were found to lie normal to the plane of the ribbon, through MFM studies. All the experimental results were discussed using the Polivanov model. © 2009 Elsevier B.V. All rights reserved.

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.

A theoretical model has been adopted to simulate the effect of temperature on surface plasmon resonance (SPR) of a gold film by modeling its dielectric functions at various temperatures. A two-prism experimental arrangement that uses Kretschmann configuration in angular interrogation mode has been used to study SPR. Reflectivity measurements as a function of temperature have been performed at different positions of the resonance spectrum. Observed intensity variations reveal a considerable sensitivity of the reflectivity towards temperature which can further be utilized for extracting thermal transport properties. © 2013 AIP Publishing LLC.

An in house designed magnetron sputtering source were described, which in turn attached to a radio-frequency (RF) power supply and used to prepare the NiFe2−xLuxO4 (x = 0, 0.075) thin films. The effects of RF power during sputtering and annealing on the structural, optical and magnetic properties of NiFe2O4 and NiFe1.925Lu0.075O4 thin films were reported. Both annealing and increasing the RF power has increased the crystallinity of the thin films. Upon annealing the films, the saturation magnetization (Ms) values of NiFe2O4 films were increased and those of NiFe1.925Lu0.075O4 films were decreased. The coercive field (Hc) values were reduced upon annealing and with increasing RF power. Both Ms and Hc values of NiFe1.925Lu0.075O4 thin films were lesser than those of NiFe2O4 thin films.