Spintronic terahertz emitter based on epitaxial thin film of kagome ferromagnet Fe 3 Sn

Magnetic quantum materials with a kagome-lattice arrangement of spins exhibit unique magnetic and electronic properties, which are closely linked to the topology of their electronic band structures. In this work we study the potential of magnetic quantum material, ${\mathrm{Fe}}₃\mathrm{Sn}$ with a kagome-lattice arrangement for terahertz spintronics. We investigate terahertz (THz) emission generated from Pt/c-plane ${\mathrm{Fe}}₃\mathrm{Sn}$ heterostructures, in which $c$ plane oriented epitaxial thin films of ${\mathrm{Fe}}₃\mathrm{Sn}$, grown on $c$-plane sapphire substrates with a Pt-seed layer, function as the ferromagnetic (FM) layer and spin source. Our measurements reveal a significant THz signal amplitude from the Pt/c-plane ${\mathrm{Fe}}₃\mathrm{Sn}$ heterostructure, which exceeds the amplitude produced by a standard 1-mm ZnTe crystal by 200%. We observe a reversal in THz signal polarity depending on the direction of pump excitation (front versus back) and the polarity of the magnetic field. These findings suggest that the mechanism behind THz emission is primarily driven by non-equilibrium spin to charge transport, consistent with mechanism of spin-to-charge conversion. Additionally, the THz emission is tunable with the angle of the external magnetic field, the thickness of the ${\mathrm{Fe}}₃\mathrm{Sn}$ layer, and the pump fluence. Unexpectedly, the THz emission from Pt/c-plane ${\mathrm{Fe}}₃\mathrm{Sn}$ remains independent of sample azimuth as well as the helicity and polarization of the incident light. This observation suggests the absence of any signature of unique quantum property of ${\mathrm{Fe}}₃\mathrm{Sn}$ such as Weyl nodes near the Fermi surface. We investigate the possible origins of this behavior and discuss its implications.