Eur. Phys. J. B 5, 37-43 (1998)
https://doi.org/10.1007/s100510050416

Magnetization dynamics below T_c of EuO and EuS^*

Evidences for effects of dipolar-anisotropic fluctuations

Institut für Angewandte Physik und Zentrum für Mikrostrukturforschung, Jungiusstr.11, 20355 Hamburg, Germany

Corresponding author: ^a goerlitz@physnet.uni-hamburg.de

Received: 4 March 1998
Accepted: 12 May 1998
Published online: 15 September 1998

Abstract

Between 4.2 K and the Curie temperatures of the cubic Heisenberg ferromagnets EuS and EuO, their homogeneous dynamic susceptibilities have been investigated by means of a broad-band reflectometer operating from 0.1 GHz to 40 GHz. For internal magnetic fields larger than the anisotropy fields of both materials, their static susceptibilities exhibit a -divergence, which reveals quantitatively the dominance of dipolar-anisotropic spin-wave fluctuations. displays a Lorentzian shape the damping frequency of which obeys scaling in terms of . The scaling function agrees quantitatively with work by Frey and Schwabl [CITE] for dipolar Heisenberg ferromagnets at temperatures above T_c. Building upon their approach, the resonance frequency of the Lorentzian can be related to a memory effect in the damping determined by the large value of the relaxation rate of the longitudinal magnetization fluctuations . For EuS, this relation is substantiated directly by inelastic neutron scattering. All these features reveal the hitherto uncovered importance of the dipolar anisotropic fluctuations below T_c of ferromagnets.