The ordering temperatures of the magnetically diluted antiferromagnetic systems K2MnpMg1−pF4 and KMnpMg1−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)[TN(p)/TN(1)] is clearly larger than 1, as is theoretically expected for diluted Heisenberg systems. The curves for TN 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 K2CopMg1−pF4 are also presented.

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In this letter it will be shown first that ’’hole trapping’’ is generally measured in such a way that the effect is only partly observed. Second, a new physical model is presented that explains this instability of the oxide charge in terms of a thermally assisted tunneling process, where electrons in neutral oxide centers are excited to states from which the electrons can tunnel to the silicon.