Quantum Magnetometry Imaging and Manipulation of Magnetic Orders in Kagome Topological (Anti-)Ferromagnets
Kagome topological (anti)ferromagnets have been identified as promising candidates for high-efficiency and low-power consumption in next-generation memory applications due to their large anomalous Hall, spin Hall and thermal transport responses [1-4]. Those originate from their sizeable Berry curvature, a fictitious magnetic field rooted in the topology and geometry of their electronic wavefunctions. The so-called ‘kagome’ lattice is a two-dimensional lattice of corner-sharing triangles, consisting of 3d transition metal atoms (T: Fe, Mn, Co) with space-filling atoms (X: Sn, Ge) at the centre of the hexagon (see Fig. a). The tight-binding band structure of kagome lattice typically exhibit Dirac points (DP) at the K-point, van Hove singularities (vHs) at the M-point, and a flat band (FB) across the whole Brillouin zone (Fig. b). The binary kagome metal series TmXn has stacking series with m:n = 3:1, 3:2 and 1:1, whereby the structural dimensionality decreases with increasing ratio of X to T (Fig. c-e). The simultaneous existence of Dirac fermions, FB and vHs in their electronic structures [3-6], makes kagome topological ferromagnets and Weyl antiferromagnets intriguing platforms to jointly study and exploit topology, correlated phenomena such as unconventional magnetic groundstates [1], and potential instabilities towards superconductivity and long-range many-body orders [2,3].
We propose to resort to a table-top state-of-the-art magnetometry technique based on a single spin nitrogen-vacancy centre to image domains, and probe domain wall dynamics under external stimuli (e.g., spin- and orbital-polarized currents, magnetic fields, temperature, mechanical stress, etc.), which together with real-space imaging and modelization should help unravel the internal domain wall structure (Néel- vs. Bloch-type) of both kagome ferromagnetic (Fe3Sn, Fe3Sn2) and antiferromagnetic (Mn3Sn, FeSn) topological systems. The nitrogen-vacancy (NV) center is an isolated quantum spin trapped in a diamond, of atomic size, with extreme (∼ 1 nT) sensitivity to magnetic fields and high spatial resolution (50 nm); across a wide temperature range [7]. Furthermore, single-spin quantum measurement protocols can be used to probe both static configurations and dynamic fluctuations.
The Ph.D candidate will use state-of-the-art facilities at the Max Planck Institute for Chemical Physics of Solids in Dresden, to grow high-quality epitaxial thin films and heterostructures by magnetron sputtering and tune the topological properties of these materials via atomically precise thickness tuning, epitaxial strain, chemical doping, and proximity induced couplings. The candidate will gain access to a broad range of structural, magnetic and electronic characterization techniques which include X-ray diffraction, atomic force microscopy, transmission electron microscopy, SQUID magnetometry, ferromagnetic resonance, magneto-optical Kerr effect, or magnetotransport (400 K - 50 mK and up to 18T).
The Ph.D candidate should have an excellent understanding of solid-state physics and materials science, a good command of spoken and written English, and be highly motivated to work in a fast-paced, collaborative and international research environment.
