A new type of spin glass in spin-density-wave CrMn alloys (abstract)

Abstract

The temperature dependence of the susceptibility χ(T)=M(T)/H of Cr1−xMnx(≪0.1<x<8% Mn) alloys in the range 5<T<400 K and in fields up to 55 kOe, measured with a SQUID magnetometer, and hysteresis of the magnetization M(H) show typical spin-glass (SG) behavior. After zero-field cooling (ZFC), χ(T) exhibits the low-T maximum typical of a SG, while cooling in the measuring field (FC) gives quite different behavior. In some cases, when measuring at low field, χ(5 K) is 10× larger in the FC state than in the ZFC state. The temperature of the irreversibility limit decreases with increasing field. All our CrMn alloys show nonlinear field dependence of M(H), with pronounced hysteresis and decay of the remanent M with time. On the other hand, these alloys exhibit properties that are essentially different from those of all other metallic spin glasses: (1) the linear scaling law based on the RKKY interaction between magnetic impurities in a typical SG is not obeyed, and indeed the temperature of the maximum in χ(T) is essentially independent of Mn concentration, which shows that formation of the SG state does not depend on the distance between the Mn atoms; (2) the maximum in χ(T) in the alloy containing only a trace of Mn (≪0.1%) is at about 40 K, a temperature at least an order of magnitude larger than that in CuMn and other metallic SG with about 0.1% impurity concentration; (3) χ(T) obeys a Curie–Weiss law above the Neel temperature, but not below, which shows that the Mn moment is frozen in the spin-density-wave (SDW) matrix We propose a model to explain this unusual behavior, in which the SG state is formed, not as a result of frustration of the Mn impurity moments, but through the frustration of the moments of the itinerant electrons of the host Cr. At low temperatures the frozen Mn moments pin the SDW, which gives rise to frustration surfaces between adjacent domains having different phase of the SDW. This effect depends only on the T-dependent interaction between the Mn moment and its neighbors, and thus is independent of the Mn concentration.