Large Sign Reversal of Tunneling Magnetoresistance in an Epitaxial Fe/MgAlO_x /Fe₄N Magnetic Tunnel Junction

A sign-reversible tunneling magnetoresistance (TMR) bestows an extra control freedom to design TMR-based spintronic devices for developing spin-logic applications. Here, we demonstrate a large sign reversal of TMR in an epitaxial Fe/MgAlOx/Fe4N magnetic tunnel junction (MTJ) controlled by the bias voltage. At room temperature (RT), the TMR is measured as large as -26.7% (-38% under optimistic definition) at V = +0.45 V, and it changes the sign to be +3.2% at V = -0.6 V. The TMR sign-reversal effect is doubled compared to those of the Fe/MgO/Fe4N MTJs, which is attributed to the better lattice mismatch between Fe4N and MgAlOx as well as less N diffusion inside the tunneling barrier. First-principles calculations reveal that the change of the TMR sign originates from different symmetry-dependent tunneling channels between Fe and Fe4N electrodes under opposite bias voltages. The Fe/MgAlOx/Fe4N MTJ with voltage-controllable TMR signs and relatively large TMR ratios at RT will promote the development of versatile and reprogrammable spin-logic applications.