The mechanism of ferromagnetic ordering in PrNi3.9Cu1.1

Mean-field approximation and perturbation theory have been employed in present work to investigate the mechanism of ferromagnetic ordering in PrNi3.9Cu1.1. We find that its magnetic behaviors in ordering phase are mainly governed by the three lowest crystal-electric-field (CEF) levels; the indirect mixtures of the excited CEF levels into the ground state due to Heisenberg exchange helps to enhance the magnetic ordering at very low temperatures; but the new excited magnetic states formed by level mixtures impede the ordering near Curie temperature, thus play very crucial and subtle roles in modulating the magnetic process in the region and especially the phase transition