OBSERVATION OF QUANTUM TUNNELING OF THE MAGNETIZATION VECTOR IN SMALL PARTICLES WITH AND WITHOUT DOMAIN WALLS: Part I

Publisher Summary This chapter presents the observation of quantum tunnelling of the magnetization vector in small particles with and without domain walls. The chapter describes an experiment and discusses the results obtained on the magnetic viscosity in Fe/Cu, Dy/Cu, Fe/Sm, and SmCo multilayers in low fields and temperatures above 1.7 K. All the systems were magnetically characterized in certain temperature range by applying low and high magnetic fields. By using this procedure, all the variations with temperature were obtained for the saturation magnetization, remanence saturation, and coercive field and information on the freezing phenomena occurring in the zero field cooled (ZFC) and field cooled (FC) processes. The relaxation experiments were done by measuring the time dependence of the sample magnetization. The magnetic measurements were performed by using a SHE SQUID magnetometer. The Fe/Cu, Dy/Cu, Fe/Sm, and Co/Sm multilayer systems were prepared by using two electron beam evaporators and a high vacuum chamber. The chapter illustrates dependence of magnetization on temperature for the samples for FC and ZFC processes when the field is applied parallel to the film plane. The main features of these measurements are the presence of a large irreversibility in the ZFC–FC processes and a broad maximum in the ZFC state. The onset of the irreversibility starts before the cusp of the peak, indicating the existence of clusters of spins involved in the freezing phenomena. During the process of relaxation, the direction of the magnetization vector changes because of the coherent rotation in single domain particles and the motion of domain walls.