Magnetic switching and magnetodynamics driven by spin transfer torque


Magnetic switching and magnetodynamics driven by spin transfer torque

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Title: Magnetic switching and magnetodynamics driven by spin transfer torque
Author: Seinige, Heidi
Abstract: In the scope of this thesis spin transfer torque (STT) driven switching and resonances in point contact experiments are investigated. In the first part, the focus is on STT driven switching events in magnetic devices with different tilt of the magnetization with respect to the thin film sample plane. Varying tilt is reached by different magnetic multilayers as Co/Ni and Co/Pt and the e efficiency of STT is compared by measuring the magneto resistance (MR) traces. As expected it was observed that tilting the magnetization of one layer with respect to the other, can improve STT efficiency. This was confirmed by micromagentic simulations using OOMMF. In the second part of this thesis, STT driven resonances in an exchange-biased spin valve (EBSV) were investigated by applying ac (microwave) and dc currents while sweeping the applied magnetic field. The resulting magnetodynamics were observed by measuring the rectified voltage which appears across the sample. To characterize the sample first the well known and understood ferromagnetic resonance (FMR) was excited. After that the power of the applied ac current was increased and a second resonance at a smaller magnetic field could be observed. This resonance structure was investigated and shown to be due to parametric resonance. This non-linear excitation appears in oscillator systems, if one or both parameter (damping, eigen frequency) oscillate in time. In the STT driven resonance experiments, the accurrent causes the damping to oscillate and therefore drives the system into parametric resonance.
Department: Physics
Subject: Spin transfer torque Magnetic switching Magnetodynamics
Date: 2011-12

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