Markayendeyulu G

The structural and magnetic properties of Nd3 (Fe1-x Alx) 27.5 Ti1.5 (x=0.1-0.4) were investigated by x-ray diffraction, magnetization, and Curie temperature (TC) measurements. The unit cell volume increases with the Al substitution, in accordance with the larger atomic radius of Al. The saturation magnetization and the Curie temperature decrease with increasing Al content, and the decrease is attributed to the modification of the density of states of 3d band due to the 3p band of Al and to the magnetic dilution effect. The easy direction of magnetization is along the b axis for x=0.4. The anisotropy field (HA) decreases with increasing Al concentration. © 2006 American Institute of Physics.

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 effect of Al on the structural and magnetic properties of Pr3 (Fe1-x Alx) 27.5 Ti1.5 (x=0.1, 0.2, and 0.3) compounds has been investigated by x-ray-diffraction, magnetization, and Curie temperature measurements. All these compounds have formed in monoclinic symmetry with A2m space group with Pr(Fe,Ti) 12 as secondary phase and traces of α-Fe. The monotonic decreases in MS both at 300 and 80 K are discussed on the basis of electron transfer from the 3p band of Al to the 3d band of Fe near EF. The variations in TC are explained using the Friedel approach. In all the compounds, the easy magnetization direction is away from the b axis. © 2006 American Institute of Physics.

Ferromagnetic and ferroelectric characteristics of Gd substituted nickel ferrite (NiO Fe1.925 Gd0.075 O3) were investigated. The material formed in the cubic inverse spinel phase and in addition, a small amount of GdFe O3 phase was identified. A small distortion of the cubic lattice was observed upon the substitution of Fe by Gd in the B site. Substitution of Gd for Fe lowered the saturation magnetization. However, the saturation magnetostriction is seen not to change significantly by the substitution of Gd. From the temperature variation of dielectric constant measurement, the ferroelectric transition temperature was found to be 512 K. The existence of the ferroelectricity was confirmed from the ferroelectric loop. The (high) dielectric constant with frequency is seen to reveal a dispersion of relaxation times. © 2008 American Institute of Physics.

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.

Magnetoresistance (Δρ ρ) studies have been carried out on the C15-type cubic Laves phase Ho0.85Tb0.15Mn2-xFex (x=0, 0.25, 0.5, 1, and 2) compounds up to a magnetic field of 90kOe at temperatures 5, 30, and 100K. The lattice parameters were found to decrease with increasing x. The Curie temperature is found to increase with increasing x from 30to680K, which is attributed to the net increase in the exchange splitting of the spin-up and spin-down bands. A maximum value of Δρ ρ of -27% was observed for Ho0.85Tb0.15Mn2 around the ordering temperature. This is explained on the basis of nearest Mn-Mn critical distance. A positive magnetoresistance, increasing in a discontinuous manner with increasing field, due to the dependence of scattering of conduction electrons on large magnetoelastic interactions, was observed at 5K in Ho0.85Tb0.15Fe2. © 2005 The American Physical Society.

A Tonpilz-type single ended transducer employing two rods of giant magnetostrictive materials has been fabricated and its underwater acoustic characteristics have been studied. The transducer resonated at a frequency of 3.1 kHz in air and at 2.65 kHz in water with a Q factor of 6. The TCR and RS at resonance in water have been measured to be 172.1 dB re 1 μPa/A at 1 m and -196.7 dB re 1 V/μPa respectively. The dimensions of the transducer are 60 mm in diameter and 110 mm long. © 1997 Elsevier Science S.A.

X-ray powder photographs on Ho0.85Tb0.15Fe 2Hx (x=0-3.1) and Dy0.73Tb 0.27Fe2Hx (x=0-3.3) revealed that there is an expansion of the lattice upon hydrogenation. Magnetization measurements were performed using a PAR vibrating sample magnetometer in the temperature range 100-700 K. The total magnetic moment is found to decrease with increase of hydrogen content. The Curie temperature of the hydrides is considerably lowered, though the exact TC in hydrides could not be determined due to desorption. Both Ho0.85Tb0.15Fe2 and Dy 0.73Tb0.27Fe2 do not exhibit any compensation, whereas Tcomp is observed and found to decreasse with x in the case of the Ho0.85Tb0.15Fe2Hx system, x=0.18-3.1. No compensation was observed even in the hydrides of the Dy 0.73Tb0.27Fe2 system. The temperature variation of magnetization of Ho0.85Tb0.15Fe2H x and Dy0.73Tb0.27Fe2Hx suggests the occurrence of a spin-reorientation transition.

The structural and magnetic properties of YGdFe17_xCox Ga (x = 0,1, 2 and 3) have been investigated through X-ray diffraction and magnetization studies. All the compounds up to x = 0.2 are formed in a single-phase, hexagonal structure. The unit cell volume decreased with the addition of Co due to the smaller size of Co than that of Fe. The magnetization and Curie-temperature values are found to increase with the addition of x and could be due to the additional Co-Co, Fe-Co exchange whose magnitude is larger compared to that of Fe-Fe exchange. Magnetically aligned sample powders indicate the presence of planar anisotropy for all the compounds. © 2006 IEEE