Markayendeyulu G

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.

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.

Large anisotropy in Dy0.73Tb0.27Fe1.5Co0.5H 0.5 when compared with Dy0.73Tb0.27Fe1.5Co0.5 has been attributed to the orientational ordering of hydrogen atoms in the lattice. Pinning effects and discontinuous jumps in magnetization have been observed at 4.2 K, up to a magnetic field of 2 kOe. The former is due to domain wall pinning and the latter is due to spin-flip metamagnetism in a field-induced transition from a modulated phase to an equal-moment phase at low temperatures. © 1997 Elsevier Science S.A.

Neutron diffraction (ND) and extended x-ray absorption fine structure (EXAFS) measurements were carried out to determine the long-range and short-range structural properties of Co-substituted Pr3Fe1-xCpxTi1. 5 compounds. ND refinement analysis indicates Ti atoms occupy the 4g and 41 Fe sites and Co atoms occupy, without preference, those Fe sites not shared with the Ti atoms. EXAFS measurements show the local environment of the Pr experiences increasing static disorder with the introduction of Co, and its coordination sphere contracts in the vicinity of those Co near neighbors. The Fe local environment remains unaffected with the introduction of Co suggesting that substitution in excess of 40% can be achieved in this structure. -. © 1999 IEEE.

The ferromagnetic resonance studies were carried out at room temperature on fine powders of Ho0.85Tb0.15Fe2Hx (x=0-3.1) and Dy0.73Tb0.27Fe2Hx (x=0-3.3) at X and Q bands. The g values were found to decrease with increasing hydrogen concentration in both the systems. This data along with the earlier magnetization and Mössbauer data have been used to explain the observance of Tcomp in the hydrogenated samples of Ho0.85Tb 0.15Fe2.

A top-loading sample chamber tube, radiation shield and the vacuum shroud for interfacing a closed-cycle helium refrigerator for use with a vibrating sample magnetometer have been designed and fabricated. A lowest temperature of 12 K is achieved at the sample. The eddy current effects in the copper sample chamber tube are minimized by the use of an electrically insulating epoxy resin medium. The sample temperature is measured by a GaAlAs diode sensor attached on a sensor mount which is inserted into the sample zone and kept in helium atmosphere. The vibrations of the cryocooler's cold head are isolated from the vibrating sample magnetometer's head by incorporating a bellows. Using this facility the magnetic transitions of some rare earth elements have been measured and compared with the literature data. © 1998 IOP Publishing Ltd.

X-ray diffraction studies carried out on MnCoxSb system revealed that the limiting value of single phase NiAs type crystal structure formation exists upto x=0.25. The variation of lattice parameters ‘a’ and ‘c’, magnetization and Curie temperature with increasing Co concentration suggests that the excess Co atoms carry magnetic moment and occupy the interstitial sites. The figure of merit evaluated from the Faraday rotation and the optical absorption coefficient at 6328 Å was found to decrease with the increase of Co concentration. © 1992, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.