Magnetic Anisotropy of Copper-Manganese Spin Glass Through Torque Measurements.

The dynamics and functional form of anisotropy energy (E(,a)) in a CuMn: 0.5 at % spin glass sample have been investigated through torque measurements. The sample is cooled through the spin glass temperature, T(,0), in an external field H(,c)(' )along (')Z. After reducing H(,c)(' )to zero and delaying for over an hour to allow the time decay of the remanent magnetization (sigma) to diminish, a measuring field H is applied 90(DEGREES) from (')Z. The anisotropy torque (GAMMA) is found to decay with at least three different exponential decay constants (tau)(,i) at several values of(' )H and temperature, T, an effect reported for the first time. The direction of the anisotropy axis (')N is found to have been redefined by the (GAMMA) decay measurement by an angle (theta)(,N)(DEGREES) with respect to (')Z. This result is contrary to the usual assumption of rigid rotations of(' )(sigma) around a fixed anisotropy axis used to analyze most previous studies of E(,a) through ESR, transverse susceptibility and (GAMMA) measurements. The direction (theta)(,N) of (')N was found to be most easily redefined at high H or T. A threshold field H(,th) = 50 Oe was found for which (theta)(,N) = 0 at T = 2.39 K. Torque curve (GAMMA) vs. (theta)(,H) measurements for H < 50 Oe showed a 2(pi) -periodicity which proves E(,a) to be unidirectional only. Both (sigma) and the unidirectional anisotropy constant K were found to decrease with increasing T.