Markayendeyulu G

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.

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.

Magnetization measurements have been performed along and perpendicular to the c-axis of Mn1.1Sb single crystal in the temperature range 293K-512K using a vibrating sample magnetometer. Spin reorientation transition has been found to occur at 380K. The temperature variation of saturation magnetization exhibited an anomaly around 380K which is attributed to the occurrence of the spin reorientation transition. The first order magnetocrystalline anisotropy constant (K1) has been evaluated employing the equation for the magnetization curve along the hard direction of magnetization. At 293K, K1is evaluated to be -6.8xl04J/m3and above 380K it is found to become positive indicating the occurrence of spin reorientation at 380K. © 1987 IEEE

This study describes the relative effect on the permanent magnet characteristics viz. remanence (B r), intrinsic coercivity (H ci), Curie temperature (T C), rectangularity of the intrinsic demagnetization curve, when Al, Cu, Ga, Nb are added individually to NdFeB. Each elemental addition causes significant improvement in H ci but the level of improvement differs from one additive element to the other. The addition of Nb is favored over other elements for realizing maximum enhancement in H ci and rectangularity of the demagnetization curve. The microstructural features of the sintered samples of NdFeB with elemental addition show the formation of a new phase, in addition to the phases (,η, Nd-rich) generally found in the ternary sample. The factors influencing the permanent magnet characteristics of sintered samples are the distribution of the Nd-rich phase in the intergranular region, the size and distribution of the minor phases at the grain junctions, the formation and distribution of new phases due to alloying addition, the solubility of the dopant element in various phases coexisting in the sample. © 2002 American Institute of Physics. © 2002 American Institute of Physics.

The results of 57Fe Mössbauer investigations carried out on the hydrogenated compounds of Dy0.73Tb0.27Fe1.5Co0.5 are presented. A change in the temperature range of the [1 0 0]-[1 1 1] spin reorientation transition from 200-290 K in Dy0.73Tb0.27Fe1.5Co0.5 to 100-150 K in Dy0.73Tb0.27Fe1.5Co0.5H 0.5 is attributed to changes in the crystalline electric field (CEF) effects resulting from the increase in rhombohedral distortions due to the orientational ordering of hydrogen atoms in the lattice. The variations in hyperfine field and isomer shift are also discussed. © 1997 Elsevier Science Ltd.

Magnetostriction and magnetomechanical coupling coefficient have been measured on Ho0.85Tb0.15Fe2-xCox (x=0, 0.5, and 1.2) alloys. The alloys were prepared by arc melting as well as by arc melting followed by zoning using induction furnace. Saturation magnetostriction (λs) and magnetomechanical coupling coefficient are found to decrease with the increase of cobalt concentration. The λs values of the zoned samples of x=0 and 0.5 are seen to be more than those of arc melted samples whereas, it is otherwise in the case of x=1.2. Magnetomechanical coupling coefficient values for all the samples are seen to increase with zoning. Change in the easy direction of magnetization in the case of x=1.2 is reflected in the magnetostriction of zoned samples.

The search for new magnetic materials with better thermal and magnetic performance led to the discovery of new intermetallic phases, R(Fe, M)12 and R3(Fe, M)29 which are known as 1:12, and 3:29 compounds. In both the compounds, the presence of a third element M (=Ti, V, Cr, Mn, Mo, W) is necessary for the stabilization of the phase. This article discusses recent investigations of structural and magnetic properties of substitutionally and interstitially modified 2:17 and 3:29 compounds.

The results of low temperature magnetization measurements carried out on the Dy0.73Tb0.27Fe2-xCox system and their hydrogenated compounds are presented. Low temperature (12 K) magnetization data reveals a large increase in anisotropy in the hydrogenated compounds, attributed to a modification in crystalline electric field effects as a result of the orientational ordering of hydrogen atoms in the lattice. The discrete step-wise increase in magnetization upto a field of 2 kOe in the parent alloys and the hydrogenated compounds is attributed to spin-flip metamagnetism. © 1998 Elsevier Science Ltd. All rights reserved.

(Sm1-xPrx)3Fe27.5Ti1.5 [x = 0.2, 0.5, 0.8, 1.0] compounds belonging to the novel 3:29 class have been prepared in order to investigate the effects of the combination of rare earths having opposite signs of second-order Stevens coefficient on their structural and magnetic properties. The amounts of different phases have been estimated from the Rietveld analysis of powder X-ray diffractograms. The changes in the easy magnetization direction in these compounds are explained as the resultant of two competing anisotropies from the rare earths occupying the two crystallographically inequivalent sites, 2a and 4i. Nitrogenation has increased the saturation magnetization and Curie temperature which could be due to magnetovolume effect and the changes in the densities of states in the 3d band. Changes in the easy magnetization direction upon nitrogenation are due to the modification of rare earth anisotropy. 57Fe Mössbauer spectra have been analyzed in a Wigner-Seitz cell approach. © 2002 Elsevier Science B.V. All rights reserved.