The European Physical Journal B

ISSN: 1434-6028 (printed version)
ISSN: 1434-6036 (electronic version)

Table of Contents

Abstract Volume 5 Issue 1 (1998) pp 37-43

Magnetization dynamics below $\mathsf{T}_\mathsf{c}$ of EuO and EuS
Evidences for effects of dipolar-anisotropic fluctuations

D. Görlitz (a), J. Kötzler

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

Received: 4 March 1998 / Accepted: 12 May 1998

Abstract: Between 4.2 K and the Curie temperatures of the cubic Heisenberg ferromagnets EuS and EuO, their homogeneous dynamic susceptibilities $\chi_{zz}(\omega,T,H)$ 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 H_A(T) of both materials, their static susceptibilities $\chi_{z}(T,H)$ exhibit a $1/\sqrt{H}$-divergence, which reveals quantitatively the dominance of dipolar-anisotropic spin-wave fluctuations. $\chi_{zz}(\omega)$ displays a Lorentzian shape the damping frequency of which obeys scaling in terms of $\chi_{z}(T,H)$.The scaling function agrees quantitatively with work by Frey and Schwabl [#!FS88!#] 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 $\Gamma_{\ell}$. 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.

PACS. 75.30.Cr Saturation moments and magnetic susceptibilities - 75.40.Cx Static properties - 75.40.Gb Dynamic properties

(a) email: goerlitz@physnet.uni-hamburg.de

Article in PDF-Format (380 KB)

Online publication: September 11, 1998
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