Transition from ferromagnetism to spin glass ordering

Abstract

Low field magnetization measurements on both weakly ferromagnetic and spin-glass like Ni-Cu and V-Fe alloys are presented. There is a qualitative difference between the two types of order in the temperature variation of the magnetization curves. In both cases the transition temperature Tc is signaled by a cusp in the a.c. susceptibility. For the ferromagnetic alloys, the height of the cusp is equal to the reciprocal demagnetization factor 1/N. For the spin glass alloys, the height depends on Tc itself: the smaller Tc, the lower the cusp. For both types of alloys, d.c. magnetization measurements reveal the onset of hysteresis at Tc. For the ferromagnetic alloys, the maximum slope of the hysteresis loop is equal to 1/N, independent of temperature for T?Tc. For the spin glass alloys, the maximum slope of the loop does not reach the 1/N limit at Tc, but continues to increase below Tc, almost reaching the 1/N limit at a lower temperature.