Low-temperature anomalies in the magnetic and thermal properties of molecular cryocrystals doped with oxygen impurity

The magnetic properties of oxygen pair clusters are investigated theoretica lly for different cluster geometries which can be realized by doping molecu lar cryomatrices with oxygen. Anomalous temperature and pressure behavior o f the magnetic susceptibility, heat capacity, and entropy is predicted. It is proposed to use these anomalies for studying the parameters characterizi ng the oxygen clusters and the parameters of the host matrix: the effective spin-figure interaction constant D for the molecule in the matrix, the exc hange parameter J, and the number of pair clusters N-p, which can deviate m arkedly from the purely random value N-p=6Nc(2) (N is Avogadro's number, an d c is the molar concentration of the impurity). The data on the magnetic s usceptibility may be used to analyze the character of the positional and or ientational short-range order in the solid solution. The value of D contain s information about the orientational order parameter; the distance and ang ular dependence of the exchange interaction parameter are still subject to discussion in the literature. The temperature dependence of N-p contains in formation about diffusion and clusterization processes in the system. (C) 2 000 American Institute of Physics. [S1063-777X(00)02009-0].