Magnetocaloric effects of 2D adsorbed O2

Abstract

Physisorbed 2D O2 shows saturation magnetisation even within magnetic fields whose magnetic energy mu .B is small compared with the thermal energy of the molecules k*T. This is demonstrated by detection of large magnetocaloric effects, which are for the first time reported for a 2D magnetic systems. The saturation magnetisation at low fields proves that Bloch's spin-wave theory for two dimensions is applicable to 2D physisorbed O2 and gives evidence for the relevance of this theory from a system which is in a much more ideal manner an approximation to 2D than the evaporated magnetic films studied up to now. In analogy to Koringa's work about nuclear-spin-lattice relaxation in the framework of nuclear magnetic cooling the authors call the observed spin-lattice non-equilibrium phenomenon the '2D Korringa effect'.