Molecular beam epitaxy growth of antiferromagnetic Kagome metal FeSn

Abstract

FeSn is a room-temperature antiferromagnet expected to host Dirac fermions in its electronic structure.The interplay of magnetic degree of freedom and the Dirac fermions makes FeSn an attractive platform for spintronics and electronic devices. While stabilization of thin film FeSn is needed for the development of such devices, there exist no previous report of epitaxial growth of single crystalline FeSn. Here we report the realization of epitaxial thin films of FeSn (001) grown by molecular beam epitaxy on single crystal SrTiO 3 (111) substrates. By combining X-ray diffraction, electrical transport, and torque magnetometry measurements, we demonstrate the high quality of these films with the residual resistivity ratio ρ xx (300 K)/ρ xx (2 K) = 24 and antiferromagnetic ordering at T N = 353 K. These developments open a pathway to manipulate the Dirac fermions in FeSn by both magnetic interactions and the electronic field effect for use in antiferromagnetic spintronics devices. a These authors contributed equally to the work.

Evidence of two-dimensional flat band at the surface of antiferromagnetic kagome metal FeSn

“…Cross-sectional transmission electron microscopy (TEM) and electron energy loss spectroscopy measurements corroborate that the films are highly crystalline down to the interface, which itself is comprised of the Fe kagome layer and Ti-rich termination layer of Nb:STO (see Supplementary Note 21). The Neel temperature of the films was found to be consistent with that of bulk singlecrystal FeSn, which exhibits a type-II antiferromagnetic spin structure [35][36][37] . When the two materials come in contact, a depletion layer is formed at the Schottky interface, creating an insulating barrier useful for tunneling measurements [38][39][40] .…”

“…Gradual depolarization of M Fe at the interface upon thermal fluctuation and the consequent reduction of the local exchange field may explain the shift from V J,peak = −180 mV at T = 2 K to V J,peak = −560 mV at T = 200 K. Model junction simulations taking into account thermal and dielectric effects give consistent positions of the flat band at each temperature (the observed V J,peak is within the simulated ranges of the flat band across the entire temperature range, see Supplementary Note 7 , 8 , 24 ). By estimating M Fe at each temperature from V J,peak , we find that the magnetic transition at the surface kagome layer effectively occurs ~316 K, reduced from the Neel temperature of FeSn extracted from bulk-sensitive measurements on single crystals ( T N,bulk ~ 365 K) 35 , 36 , 60 , 64 and thin films ( T N,film ~ 358 K) 37 , 65 . The modulation of the flat band position as a function of the size of the spin moment suggests a possibility of engineering the chemical potential of an arbitrary magnetic kagome compound to the position of the flat band with a fine balance of thermal fluctuation, disorder, and magnetic field.…”

“…Planar tunneling spectroscopy measurements. Epitaxial thin films of FeSn were deposited on Nb:STO with varying Nb concentrations (x = 0.05, 0.2, 0.5, 0.7 wt.%) by MBE 37 (see Methods). X-ray diffraction measurements confirmed the formation of (001) oriented FeSn films with in-plane crystallographic orientation epitaxially locked to that of Nb:STO (see Supplementary Note 3,20).…”

Recent Progress on 2D Kagome Magnets: Binary TmSnn (T = Fe, Co, Mn)

“…was the first to achieve high‐quality epitaxial growth of FeSn(001) thin films on a SrTiO 3 (111) single crystal substrate, which is covered with amorphous BaF 2 . [ 58 ] They found that post‐annealing can improve the quality of FeSn films, and the sample quality is not affected by the device manufacturing process. They suggested that the quadratic parabolic negative magnetoresistance of FeSn thin films may be caused by the modulation of the resistance by its antiferromagnetism (Figure 8f).…”

“…Reproduced with permission. [58] Copyright 2020, AIP Publishing. films on a SrTiO 3 (111) single crystal substrate, which is covered with amorphous BaF 2 .…”