Current induced domain wall motion at the magnetic compensation point in Manganese Nickel Nitride (MnNiN) thin films

Abstract

Spintronics has developed into a growing field with the fabrication of magnetic memories and logic devices. Domain wall motion is a major part of the research in spintronics where spin polarized current is used to move the domain walls by two mechanisms spin tranfer torque(STT) and spin orbit torque(SOT). Compensated ferrimagnets have been in focus recently for their ability to reach the magnetic and angular compensation points. At the angular compensation point, the precessional motion of the local magnetic moment becomes negligible which massively enhances the domain wall velocity near this point[1,2]. In our previous studies, we had shown epitaxially grown ferrimagnet Manganese Nitride(Mn4N) having an anti-perovskite crystal structure with Mn atoms at the corner and the face centre sites while Nitrogen atom in the centre[3]. It has a very low magnetization (71kA/m) and a high perpendicular magnetic anisotropy(PMA) with mm sized domains[3]. Such small magnetization and high PMA is necessary for faster domain wall motion. Such properties led us to observe a very high domain wall velocity of 900 m/s at 1.2*1012 A/m2 [4] using pure STT. Here we report an even larger domain wall velocity of more than 2000 m/s at 1.16*1012 A/m2 using pure adiabatic STT near the magnetic and angular compensation point in epitaxially grown Ni substituted Mn4N nanowires (MnNiN). We also show a very small thresold current density of 1*1011 A/m2. This high speed is comparable to the best velocities obtained by SOT with the assitance of an external in-plane field. In our case, such domain wall velocity is achieved without any external in-plane field, with the sole action of pure current in this single layer system. Addtionally, we also show a reversal in the direction of the domain wall motion after the magnetic compensation point, where the domain walls move in the same direction as the current. We discuss this reversal of the domain wall motion phenomena with the help of DFT calculations.