Some experiments on magnetically diluted antiferromagnets

Abstract

Experiments are reported on the magnetically diluted systems KMn p Mg 1− p F 3, K 2Mn p Mg 1− p F 4 and K 2Co p Mg 1− p F 4. To a good approximation the concentrated compounds ( p = 1) are examples of simple cubic Heisenberg, simple quadratic Heisenberg and simple quadratic Ising antiferromagnets, respectively. The dependence of the ordering temperature on the concentration of magnetic ions has been discussed in a previous paper already. In the present paper special attention is given to the field and temperature dependence of the low-temperature susceptibility. It appears that in this respect there is a clear difference between the diluted Heisenberg and Ising compounds, respectively. Whereas the diluted Ising system behaves relatively simple, the concentration dependence of the susceptibility of the Heisenberg compounds reflects in a sense the critical (ordering) behaviour of the system. The consequence of a variation of the exchange constant with lattice parameter, as indicated experimentally, is discussed.