M. Huq

The determination of magnetic anisotropy constants from torque curves

Abstract The procedures by which magnetic anisotropy constants are evaluated from torque curves are examined with reference to some calculated torque curves for an ideal uniaxial crystal. The results are compared with some torque measurements on a crystal of cobalt.

The determination of anisotropy constants from torque curves — II

Abstract This is an extension of a previous paper which examined the methods available for the determination of the anisotropy constant from torque curves when the anisotropy is governed by a single constant i.e. E = K 1 sin 2 φ. The two methods singled out in that paper as being of special merit are briefly re-examined when the anisotropy energy takes the form E = K 1 sin 2 φ + K 2 sin 4 φ.

The effect of crystallization on the low-temperature specific heat of an amorphous polymer

Abstract The specific heat of amorphous polythylene terephthalate between 1.2 and 4.2 K is found to be higher than the Debye acoustic value. On crystallization this excess specific heat decreases in proportion to the decreasing amorphous content indicating that localized vibrational modes in the amorphous phase are responsible for this contribution.

Low temperature specific heats and susceptibilities of some dilute palladium based alloys

Abstract Measurements are reported of the low temperature (1–4 K) specific heats of dilute Pd based binary alloys containing Ag, Rh, Ru, Mo and Nb, the principal objective being to determine γ, the coefficient of the term proportional to temperature. Some measurements of high field susceptibility at 4 K are included.

Effect Of Cr Substitution On The Magnetotransport Properties Of La0.7Ca0.3MnO3

The structure and phase purity of powder La0.7Ca0.3Mn1−xCrxO3 (x = 0.075, 0.15, 0.3), has been by checked by X‐ray diffraction. Effects of Cr doping on the magnetic and transport properties are studied in the range 300—4 K in the absence and presence of 0.7 T magnetic field. All the samples show metral‐insulator transition behaviour with a peak in the electrical resistivity as the temperature is decreased. For increasing doping concentration an increase in resistivity, a decrease the resistivity peak temperature to the metal‐insulator transition and an increase in low temperature intrinsic magnetoresistance is observed. The activation energy which explains the insulating like behaviour of resistivity above transition temperature is calculated and compared with the Cr concentration.

Re‐entrant Spin Glass And Spin Glass Behavior Of Diluted Mg‐Zn Ferrites

Field cooled and zero field cooled dc magnetization, temperature and frequency dependence of ac susceptibility on diluted Mg‐Zn ferrites prepared by the solid state reaction method is reported. Samples with x = 0.6, 0.7 and 0.8 show re‐entrant spin glass behaviour while the samples with x = 0.9 and 1.0 show typical spin glass behaviour with the manifestation of non‐equilibrium dynamics of the spin glass such as aging, rejuvenation and memory effects.

OBSERVATION OF HIGH Tc IN THE BILAYERED La2SmxSr1-xMn2O7 PEROVSKITE

Bulk layered perovskite samples La2SmxSr1-xMn2O7 (x = 0.4, 0.6 and 0.8) were prepared by the conventional solid-state reaction technique and their temperature dependence of electrical resistance and magnetization measurements were performed. The metal-insulator (M-I) transition, magnetic phase transition and the colossal magnetoresisitance phenomena were observed. The M-I transition peak temperature (Tp) shifts towards lower temperature with increasing x while magnetic field shifts Tp to the high temperature regime. Experimental results show that layered manganites La2SmxSr1-xMn2O7 (x = 0.4, 0.6 and 0.8) exhibit ferromagnetic-to-paramagnetic transitions at Curie temperature Tc ~ 355, 286 and 277 K for x = 0.4, 0.6 and 0.8, respectively. A large deviation between the metal-insulator transition and the magnetic transition temperature is observed for all the doping concentrations. But in the case of well-known ABO3 type perovskite manganites like La0.75Ca0.25MnO3, the M-I transition was found previously very...