Ordering in Two- and Three-Dimensional Diluted Heisenberg Antiferromagnets

Abstract

The ordering temperatures of the magnetically diluted antiferromagnetic systems K₂Mn_pMg_1−pF₄ and KMn_pMg_1−pF₃ are presented. From a magnetic point of view these systems can be looked upon as being simple quadratic and simple cubic, respectively. Near p=1, (d/dp)[T_N(p)/T_N(1)] is clearly larger than 1, as is theoretically expected for diluted Heisenberg systems. The curves for T_N as a function of the concentration show that the critical concentrations for ordering at T=0 are clearly different for the two magnetic systems; they may be equal to the values predicted for the percolation problem. The low‐field perpendicular susceptibility strongly depends on p, at the lower temperatures it can be approximately described by a kind of Curie‐Weiss law. Extrapolating the Curie‐Weiss behavior down to T=0, one obtains values for the inverse perpendicular susceptibility that, if plotted as a function of the concentration of magnetic atoms, show a clear similarity to the concentration dependence of the ordering temperature itself. Some results of the two‐dimensional nearly Ising system K₂Co_pMg_1−pF₄ are also presented.