Crystal-field-induced magnetostrictions in the spin reorientation process of Nd2Fe14B-type compounds

Volume expansion $ΔV / V$ associated with the spin reorientation process of Nd$_2$Fe$₁₄$B-type compounds has been investigated in terms of simple crystalline-electric-field (CEF) model. In this system, $ΔV / V$ is shown to be a direct measure of second order CEF energy. Calculated anomalies in $ΔV / V$ associated with the first-order magnetization process of Nd$_2$Fe$₁₄$B are presented, which well reproduced the observations.