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Title:1/F Noise & slow spin dynamics in chromium, chromium alloys, and disordered iron zirconium
Author(s):Michel, Richard Paul
Doctoral Committee Chair(s):Weissman, Michael B.
Department / Program:Physics
Subject(s):spin dynamics
chromium alloys
iron zirconium
spin density wave polarization dynamics
Abstract:1/f resistance noise studies of the spin dynamics in two magnetic systems are described in this thesis. In chromium, 1 If noise was used as a probe to study spin density wave polarization dynamics. Measurements of the noise anisotropy in a high quality single crystal of Cr revealed a temperature range where polarization dynamics were the dominant source of 1 If noise. In this temperature range, discrete switching was observed in the resistance of mesoscopic samples of Cr. This observation verified the existence of stable spin density wave polarization domains. In CrMn the domain dynamics which were found in the incommensurate SDW phase were absent in the commensurate phase. This absence indicates that incommensurability plays a crucial role in the polarization domain dynamics. Amorphous FeZr undergoes two magnetic phase transitions which were studied using 1 If noise. The first transition is from a paramagnetic to a ferromagnetic phase. The noise observed in disordered FeZr films near T c was non-linear and non-Gaussian and indicated the presence of fluctuating ferromagnetic domains. The domains were sensitive to the small magnetic fields induced by the ac probe current. At the temperature of the second reentrant transition, Tf, the system enters a disordered spin glass phase. At Tf the noise rose nearly an order of magnitude, and was linear and Gaussian. By comparing the spectral slope and the temperature dependence of the noise near T f , the degree to which the transition deviated from thermally activated behavior was quantified. Measurements of the resistance noise in mesoscopic constrictions of FeZr revealed interesting hydrogen motion in the system which obscured the effects of the spin dynamics on the resistance.
Issue Date:1994
Genre:Dissertation / Thesis
Rights Information:Copyright 1994 Richard Paul Michel
Date Available in IDEALS:2011-04-21
Identifier in Online Catalog:3644705

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