Speaker
Description
Van der Waals metallic ferromagnets (e.g. CrxTey, Fe3GeTe2) with a Curie temperature near 300 K are a new addition to the family of 2D materials. They possess perpendicular magnetic anisotropy down to a few monolayer regime and are reported to host skyrmions. Their combination with spin orbit torque materials (e.g. topological insulators (TI)) may lead to efficient charge to spin conversion for spintronic devices. Apart from technology, there is great scientific interest to correlate the observed large anomalous Hall effect (AHE) with the electronic bandstructure and the possible non-trivial topology of these materials. The broken time reversal symmetry in magnetic materials generates a large Berry curvature (BC) at (near) energy degeneracy points where the metallic bands cross. The latter quantity acts as an effective magnetic field in reciprocal space producing anomalous Hall currents without external magnetic field.
We will first present our DFT band structure calculations for the and Cr2Te3, Fe3GeTe2. Then, we will describe the wafer scale epitaxial growth [1,2] of the 2D ferromagnets/Bi2Te3 TI [3] combinations on different substrates by MBE and we will show evidence of their structural quality by in-situ STM, RHEED and ex-situ Raman and XRD. The band structure is imaged by in-situ ARPES and compared with theoretical calculations. Based on magnetic hysteresis measurements (SQUID, AHE), the optimum growth temperature, layer thickness and substrate are identified for spin torque and efficient charge to spin conversion. The measured AHE is correlated with DFT calculations of anomalous Hall conductivity originating from sizeable BC in these materials.
Acknowledgements: H2020 FET PROAC project SKYTOP; H2020 MSCA ITN project SMART-X
References
[1] H. Li et al., ACS Appl. Nanomaterials DOI: 101021/acsnm 9b01179 (2019)
[2] H. Wang et al., ACS Nano 14, 10045 (2020)
[3] S. Fragkos et al., Phys. Rev. Materials 5, 014203 (2021)
