We study the microwave-induced magnetization reversal in two systems, the microwave-driven nanomagnet (NM-MW) and the nanomagnet coupled to a Josephson junction under the microwave field (NM-JJ-MW). The frequency of the applied cosine chirp pulse (CCP) changes nonlinearly with time to match the magnetization precession frequency. The coupling between the nanomagnet and Josephson junction reduces the magnetization switching time as well as the optimal amplitude of the microwave field as a result of manipulating the magnetization via Josephson-to-magnetic energy ratio G. The reversal effect in NM-JJ-MW is sufficiently robust against changes in pulse amplitude and duration. In this system, the increase of G decreases the possibility of the non-reversing magnetic response as the Gilbert damping increases without further increase in the external microwave field. We also discuss the magnetic response of the nanomagnet driven by the ac field of two Josephson junctions in which the time-dependent frequency is controlled by the voltage across the junctions. Our results provide a controllable scheme of magnetization reversal that might help to realize fast memory devices.

Abstract:In this paper, we suggest a conventional semiclassical approximation to calculate several thermodynamic quantities of a rotating Bose-Einstein condensation in a deep optical lattice. Expressions for the condensation fraction, critical temperature, and heat capacity are derived analytically.