Tuning functionality in epitaxial topological kagome heterostructures

Prajwal M. Laxmeesha

doi:10.17918/00011082

Quantum materials hold great promise to meet the growing demand for computer processing power and storage by coupling the spin degree-of-freedom and charge transport properties of electrons for use in spintronic devices. Of these, kagome metals -- materials with a trihexagonal sublattice -- offers a unique platform to explore electron correlation and band topology within the same materials. To leverage upon these characteristics and realize next-generation integrated non-volatile memory and storage, it is crucial to synthesize high-quality heterostructures and control the functional properties of the materials that make them up. In this work, I showcase the progress I've made in thin film synthesis of multiple kagome materials-based heterostructures such as FeSn, Fe₃Sn₂ and CoSn via molecular beam epitaxy (MBE) on insulating oxide substrates, with a special focus on antiferromagnetic FeSn which exhibits strong exchange bias when coupled with an adjacent ferromagnet, confirmed using magnetometry. Using a combination of high-resolution x-ray diffraction, reflection high-energy electron diffraction, and electron microscopy I demonstrate that the FeSn films are flat, continuous and epitaxial. Furthermore, I will discuss doping strategies that allow for the tuning of electronic and magnetic properties such as alloying and interfacial charge transfer. Specifically in Fe₃Sn₂ and FeSn, I demonstrate successful hole doping achieved by alloying the two materials with Mn, leading to Fe_[3-x]Mn_xSn₂ and Fe_[1-x]Mn_xSn random alloys and examine their magnetic properties. Through the use of synchrotron-based X-ray magnetic circular dichroism (XMCD) I show the means to directly probe elemental contribution to magnetism in Fe_[3-x]Mn_xSn₂, disentangling both spin and orbital moments, and using neutron diffraction, I show suppressed Curie temperature in Fe_[1-x]Mn_xSn. I also report on the synthesis of all-kagome (Fe₃Sn₂)_m/(CoSn)_n superlattices, an alternative route to electron dope these materials, and using polarized neutron reflectometry, I test the hypothesis that ferromagnetism in Fe₃Sn₂ persists even when the film thickness is less than a single unit cell. These advanced characterization techniques provide exceptional insight into magnetic behavior globally across complex heterostructures and at localized interfaces, enabling a thorough understanding of the underlying magnetic phenomena.

Tuning functionality in epitaxial topological kagome heterostructures

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Tuning functionality in epitaxial topological kagome heterostructures

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