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Temporal Dynamics of the Mixed Magnetic Phase of B2-Ordered FeRh

Massey, Jamie Robert (2019) Temporal Dynamics of the Mixed Magnetic Phase of B2-Ordered FeRh. PhD thesis, University of Leeds.

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Abstract

B2-ordered FeRh undergoes a first-order metamagnetic transition from an antiferromagnet (AF) to a ferromagnet (FM) upon heating. Thin films of B2-ordered FeRh are grown using DC magnetron sputtering and characterized for their behaviour at GHz frequencies and their dynamic behaviour over hour timescales. Ferromagnetic resonance investigations reveal a change in the spectroscopic splitting factor, g, through the range of the transition probed here. By introducing a model that describes the development of the two magnetic phases through the transition, this change in g is shown to be consistent with the development of an exchange coupling across the magnetic phase boundary that induces a non-zero magnetic moment in the AF phase as the result of a thickness dependent phase transition in the AF layer. The influence of such a phase transition is also seen in the extracted value of the Gilbert damping parameter in this experiment. Spin-wave resonance measurements are then performed to try and conclusively measure the exchange coupling between the two magnetic states in FeRh. Measuring the exchange stiffness through the transition reveals that the AF phase has a non-zero exchange energy that varies through the measurement range probed here. The behaviour of the exchange stiffness in the AF layer is attributed to a combination of both the onset of the exchange coupling and the presence of evanescent spin-waves, both of which are consequences of the thickness dependent phase transition in the AF layer. It was then shown that the structure of both magnetic phases could be measured directly with X-Ray Magnetic Dichroism using both linearly and circularly polarized light. The objects measured in these experiments are then characterized for their dynamic properties using X-Ray Photon Correlation Spectroscopy. These studies reveal reveal that the dynamic behaviour of the system is dependent on the type of magnetic dichroism used to probe it. This study also shows it is possible use x-ray magnetic linear dichroism to directly measure the structural and dynamic behaviour of AF materials.

Item Type: Thesis (PhD)
Keywords: FeRh, XMCD, XPCS, XMLD, Magnetization Dynamics, FMR, SWR.
Academic Units: The University of Leeds > Faculty of Maths and Physical Sciences (Leeds)
The University of Leeds > Faculty of Maths and Physical Sciences (Leeds) > School of Physics and Astronomy (Leeds)
Identification Number/EthosID: uk.bl.ethos.786534
Depositing User: Mr Jamie Robert Massey
Date Deposited: 27 Sep 2019 15:55
Last Modified: 18 Feb 2020 12:50
URI: http://etheses.whiterose.ac.uk/id/eprint/24877

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