Temperature Dependence of Two-Terminal Local Magnetoresistance in Co-Based Heusler Alloy/Ge Lateral Spin-Valve Devices

Abstract

We investigate temperature dependence of two-terminal local magnetoresistance (MR) effect for germanium (Ge)-based lateral spin-valve (LSV) devices with three different ferromagnet (FM)/Ge Schottky tunnel contacts. When we insert a 0.7-nm-thick Fe layer between Co-based Heusler alloy and Ge interfaces in LSV devices, the magnitude of the local MR signals is significantly improved from low temperatures to room temperature. However, the temperature dependence of the MR ratio is still large even for LSV devices with Fe insertion. From the analysis based on the standard theory, the temperature-dependent MR ratio can be interpreted in terms of thermally excited spin waves ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T^{3/{2}}$ </tex-math></inline-formula> law) in FM contacts. The physical origin of the decay of the two-terminal MR ratio in Ge-based LSV devices is the same as that of the four-terminal nonlocal spin signals because small temperature dependence of contact resistance is demonstrated in FM/Ge Schottky tunnel contacts which show almost linear <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$|J|$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V$ </tex-math></inline-formula> characteristics and low interface resistance.