The reversible susceptibilities of dysprosium and terbium

Abstract

The initial susceptibilities of Dy and Tb have been measured in the ferromagnetic and antiferromagnetic phases. In the ferromagnetic phase it is concluded that the susceptibility arises from domain wall displacements and that these are limited by an intrinsic restoring force resulting from the very narrow domain wall and not by local impedances due to imperfections and impurities. From measurements in the antiferromagnetic phase it is concluded that the often quoted two constant expression for the exchange coupling between sublattices cannot provide a quantitative explanation for the observed behaviour but that the susceptibility of Dy and the temperature variation is quantitatively consistent with the seven exchange constants and the turn angles determined from neutron scattering measurements. The reversible susceptibility measured in the presence of external fields shows a complicated behaviour and does not appear to be consistent with the predictions of the theory of Nagamiya et al. (1962).