Unconventional bias-dependent tunneling magnetoresistance in van der Waals ferromagnetic/semiconductor heterojunctions

Two-dimensional van der Waals (vdW) ferromagnetic/semiconductor heterojunctions provide an ideal platform for studying and exploiting tunneling magnetoresistance (TMR) effects, due to the versatile band structure of semiconductors and high quality of their interfaces. In all-vdW magnetic tunnel junction (MTJ) devices, both the magnitude and sign of TMR can be tuned by an applied voltage. Typically, as the bias voltage increases, the amplitude of TMR initially decreases, followed by a reversal and/or oscillation in its sign. Herein, we report on an unconventional bias-dependent TMR observed in all-vdW Fe3GaTe2/GaSe/Fe3GaTe2 MTJs, where TMR first increases, then decreases, and ultimately undergoes a sign reversal as the bias voltage increases. By considering the coherent degree of in-plane electron momentum $${{{{\bf{k}}}}}_{{{\parallel }}}$$ and the decay of the electron wave function through the semiconductor spacer layer, our theoretical prediction successfully explains this unconventional bias-dependent TMR. Consequently, our results offer a deeper understanding of bias-dependent spin-transport in semiconductor-based MTJs and provide new insights into semiconductor spintronics. The combination of a diverse selection of magnetic and semiconducting constituent materials makes van der Waals heterojunctions ideal for exploring effects associated with tunnelling magnetoresistance. Here, Zhu, Wen, Zhu, Cui, and coauthors report on a unusual bias dependence of tunnelling magnetoresistance, that they explain via a planar dependent tunnelling model.