Two-phase granular materials: magnetisation kinetics and magnetoresistance

Dennis Geoghegan

Research output: ThesisDoctoral Thesis

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Abstract

[Truncated] I have prepared antiferromagnetic/ferromagnetic nano-composites of CoO/Co and NiO/Niby mechanical milling and ribbons of Au-Co alloys by melt-spinning. The CoO/Co andNiO/Ni materials were subjected to heat treatment at temperatures ranging from 400°Cto 900° C for 1 h resulting in typical grain sizes of 20 nm. The Au-Co ribbons were heat treated at 400°C for total times of heat treatment ranging from 10 min to 8 h resulting in the formation and eventual dissolution of a multilayer-like eutectic structure. X-ray diffraction was used to determine the solid phases present in the samples and electron microscopy(scanning and transmission) was used to determine the microstructure of the Au-Co ribbons.
For the CoO/Co samples, it is shown that the exchange coupling between the CoO and Co grains leads to exchange anisotropy which was determined by observing both Curie point-like transitions in the temperature dependence of remanent magnetisation curves and displaced hysteresis loops upon cooling the sample through the Neel temperature of CoO in an applied field. Magnetic viscosity measurements at room temperature were made on the NiO/Ni samples on both the major hysteresis loop and on the lower branches of the recoil curves. An experimental procedure to measure anomalous magnetic viscosity was designed and anomalous magnetic viscosity was measured. In this case the time dependence of magnetisation is initially away from the anhysteretic magnetisation curve before going through a turning point and approaching the anhysteretic magnetisation curve.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • The University of Western Australia
DOIs
Publication statusUnpublished - 1997

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