Magnetization Dynamics in a Permalloy Disc and Nanowire

Abstract

In this work, the magnetization dynamics in a nano scale Permalloy disc and nanowire. This work is mainly consists of two parts. First part is the experimental investigations of the magnetic vortex core dynamics excited by microwave currents on a magnetic disc. Second part is the numerical calculations of the magnetization dynamics with propagating spin waves.For the measurements, the homodyne detection scheme is used. This technique is based on the microwave current rectifying effect. The cryostat system is able to control the sample temperature from 2 K to 500 K and the microwave frequency is controlled from DC to 20 GHz. First the chirality and polarity of the vortex core are determined. From the systematic field dependent measurements, the strong pinning effects are ascertained at the certain position of the vortex core. The temperature and microwave power dependence confirm the pinning effects. This pinning effect allows us to calculate the potential landscape of our system. From the analysis of the phase shift between the microwave current and the magnetoresistance response, the Oersted field contribution to the vortex core dynamics is determined. The Oersted field is about 75 % of the force exerted on the vortex core gyration.The interaction between propagating spin waves and domain walls are numerically investigated by using micromagnetic simulations. In order to understand the mechanisms that lead domain wall motions, the domain wall velocity by spin waves, the spin wave dispersion relation, and the depinnig fields for pinned domain wall are calculated. The physical origin of the spin wave induced domain wall motion strongly depends on the propagating spin wave frequency. At certain spin wave frequencies, transverse domain wall oscillations lead to transverse wall displacement by the spin waves, while at other frequencies, large reflection and effective momentum transfer are main drivers of the spin wave induced domain wall motion. The oscillating Oersted field generated by microwave current injection is investigated as a new spin wave source.