TEMPERATURE AND FIELD-DEPENDENCE OF DOMAIN-WALL DYNAMICS UP TO THE CURIE-POINT OF EUO

Using a broadband vectorial microwave reflectometer, the dynamic susce ptibility has been measured on a EuO sphere in the range from 0.3 to 2 0 GHz. The data taken at zero field between 4.2 K and the Curie temper ature T-c=69.5 K were analyzed using a phenomenological model of a dam ped harmonic oscillator for the domain walls, that has been successful ly applied to the early investigations on ferrites. Based on the micro magnetic Landau-Lifshitz (LL) model, the temperature variation of the intrinsic resonance and damping frequencies are explained up to T=0.98 T-c. The resulting LL-kinetic coefficient, L(perpendicular to)=1.1X10 (11) s(-1), remains independent of temperature and is related to the d ipolar induced relaxation rate of the longitudinal magnetization fluct uations. In fields along the easy [111] axis and the symmetric [100] d irection this wall process prevails for magnetizations smaller than M( s)/4 and M(s)/root 3 respectively. Above these thresholds, the charact eristic frequencies of the dominant process decrease with field, possi bly due to rotational dynamics, and for H parallel to[111] a second dy namics associated with the paraprocess is contributing. (C) 1996 Ameri can Institute of Physics.