X-ray and microwave studies of strongly exchange coupled magnetic multilayers

Abstract

Magnetic exchange spring systems which consist of alternating thin hard and soft magnetic layers provide a great potential in applications such as (i) permanent magnets and (ii) magnetic data storage. The molecular beam epitaxy-grown samples provide an excellent model system with which to study the magnetic switchings and reversals. X-ray magnetic circular dichroism (XMCD) allows element-selective hysteresis loops with the results presented alongside bulk magnetometry and micromagnetic modelling. This gives a complete picture of REFe2 magnetic exchange springs. This work unveiled the spin-flop and transverse exchange springs in the ErFe2/YFe2 and DyFe2/Fe2 thin film multilayers respectively.

This work has also focused upon studying the magnetisation dynamics of exchange-coupled bilayers. Ferromagnetic resonance spectroscopy gives multiple resonant modes of the NiFe/CoFe exchange-coupled bilayer. X-ray detected ferromagnetic resonance was used to investigate the relationship between the magnetic layers by using XMCD for the magnetic contrast. How the anisotropy of one layer can influence the second, as well as determination of the origin of the two resonant modes are discussed.

A new microwave device is the final aspect of this work. The new topic of metamaterials was studied and opened up new research directions. This work demonstrates that tunability of the metamaterial resonance by applied magnetic field is possible by coupling the resonant split ring resonator structure to magnetic thin films, providing large modulations in transmitted microwave power previously unattained.

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