Interface tailoring effect on magnetic properties and their utilization in MnGa-based perpendicular magnetic tunnel junctions

Abstract

Insertion of a thin 3$\mathit{\text{d}}$ ferromagnetic metal/alloy layer between the barrier layer and the perpendicularly magnetized ferromagnetic electrode is an effective method to enhance the magnetoresistance (MR) ratio in perpendicular magnetic tunnel junctions (p-MTJs). In the present paper we systematically studied the structural and magnetic properties as well as the spin-dependent transport in p-MTJs with a core structure MnGa/FM/MgO/CoFeB (FM $=$ Fe, Co), with the MnGa being the $\mathit{\text{L}}{1}_{0}$ MnGa alloy ($M{n}_{57}G{a}_{43}$, $M{n}_{62}G{a}_{38}$) and the $\mathit{\text{D}}{0}_{22}$ MnGa alloy ($M{n}_{70}G{a}_{30}$). The insertion of the Fe and Co layers enhances the MR ratio significantly as well as the MnGa composition dependence of the MR ratio. In addition, opposite magnetic properties and $\mathit{\text{MR}}$($\mathit{\text{H}}$) curves of MTJs with Fe and Co interlayers are observed, naturally suggesting the ferromagnetic and antiferromagnetic exchange coupling for MnGa/Fe(bcc) and MnGa/Co(bcc), respectively. By considering the exchange coupling between the FM and MnGa, we successfully simulated the $\mathit{MR}$($\mathit{\text{H}}$) curves of the samples with Fe and Co interlayers based on a simple model. Furthermore, the interlayer effect on the transport properties are discussed based on the temperature dependence of the MR ratio by using the magnon excitation model modified with impurity-induced hopping. It shows that the FM interlayer restrains the impurity induced hopping and the magnon excitation; and furthermore, the Co is more effective in restraining the impurity diffusion and magnon excitation as compared to Fe.