The spin s=7/2 FCC ferromagnet: comparison between cluster variation method and Monte Carlo calculations

Internal energy, reduced magnetisation, point probabilities and specific heat capacity have been calculated for the hexagonal close packed (HCP) Ising ferromagnet with spin 7/2 using the Monte Carlo (MC) method in the isotropic nearest neighbour approximation for a 48×48×48 computer crystal. The results are compared with previously published calculations obtained for the face-centred cubic (FCC) structure from the cluster variation method (CVM) in the tetrahedron approximation. Internal energy, reduced magnetisation and point probabilities obtained from MC and CVM are almost identical in a large range of temperatures both above and below the Curie temperature (TC). A slight difference appears only in the critical region close to TC. The specific heat capacity has been calculated at temperatures above TC. In this paramagnetic region the MC calculations yield considerably higher values than the CVM, leading to a better agreement with experimental data for Gadolinium than previously obtained with the CVM.