Monte Carlo simulation of the surface magnetic phase transition in chromium

摘要

Antiferromagnetic chromium is known to have a surface magnetic phase transition at a temperature T(sub s) = 780K, which is well above its bulk Neel temperature, T(sub N) = 311K. Electronic structure calculations predict an enhancement of the magnetic moment at the surface, due to changes in the local electronic environment. In order to ascertain the role of such an enhancement in the surface magnetic transition, we have modelled the surface by means of a classical Heisenberg model in which: (a) the magnitude of a given spin is equal to the value of the corresponding magnetic moment predicted by band structure calculations, (b) the exchange interaction J between spins is the same throughout the system, and (c) the exchange interaction is chosen so as to reproduce the bulk transition temperature. We find a ratio of surface to bulk transition temperature of T(sub S)/T(sub N) = 2.5, which is an excellent agreement with the experimental result. Our results suggest that the surface magnetic transition in chromium is driven by fluctuations in the orientation of the magnetic moments and that quantum fluctuations play a minor role. (author). 18 refs, 5 figs. (Atomindex citation 26:046213)