Experimental estimation of the spin diffusion length in undoped p-Ge on Fe3Si using vertical spin-valve devices

Abstract

Using vertical spin-valve devices, we experimentally investigate the room-temperature spin diffusion length in an undoped p-Ge layer grown on ferromagnetic Fe3Si. Because low-temperature molecular beam epitaxy techniques enable us to grow vertically stacked and all-epitaxial CoFe/Ge/Fe3Si trilayers on Si(111), we can intentionally vary the thickness (tGe) of the intermediate undoped p-Ge layer during the growth. With decreasing tGe, the magnitude of the spin signals gradually increases at room temperature. From the analysis based on the model by Fert and Jaffrès, the room-temperature spin diffusion length in the undoped p-Ge grown on Fe3Si is experimentally estimated to be ∼8.4 nm, much shorter than those reported in previous works on commercial p-Ge substrates.