Experimental and theoretical approach to magneto-transport properties in Mn4-xNixN with high domain wall mobility

Abstract

In recent years, current-induced domain wall motion (CIDWM) is attractive research field in spintronics because it’s expected to enable magnetic non-volatile memory. Our group focuses on Mn4N and its based nitrides as new candidates for CIDWM application. Especially, Mn4-xNixN nanowire recorded a DW velocity of 3,000 m/s only by spin-transfer torque [1]. We attributed this to the compensation of Mn4-xNixN around x=0.2 [2]. In spite of the excellent CIDWM, magneto-transport properties in Mn4-xNixN have scarcely been reported. In this work, we report both experimental and theoretical investigations of these properties with anisotropic magnetoresistance (AMR) measurement and calculation of PDOS with Vienna Ab initio Simulation Package (VASP). Figure 1 shows Fourier coefficients of AMR measurements in Mn4-xNixN on SrTiO3(001) substrates and energy state of d electrons under various crystal fields. C2 represents the coefficient of cos2θ component and C4 does that of cos4θ, where θ is the angle made by the current and the magnetization. Above 100K, small C2 components dominate AMR while C4 drastically became large below 100K. This represents the emergence of the tetragonal-like crystal field below 100K because it depends on the difference in PDOS between dxy and dyz, dzx states [3]. However, this trend was weakened by large Ni composition. Figure 2 shows PDOSs of d orbitals in Mn and Ni at corner site (I-site) in Mn4-xNixN (x=0, 0.5). By Ni substitution, spin polarization of d orbitals decreased at Fermi level (EF). This leads to decrease in both AMR ratio and C4 components, derived from the theory of s-d scattering [4]. In the previous study, the emergence of C4 components in Mn4N was attributable to the possible external effect such as lattice strain caused by the thermal expansion [3,4]. However, since all structures were set to be cubic in our calculation, we expect this is attributable to intrinsic change in PDOS, and dramatically affected by Ni doping. In the talk, we’re going to further investigate the modulation of Hall effect in Mn4-xNixN by Ni composiiton.  Fig. 1 Fourier coeffcients of AMR in Mn4-xNixN and energy state of d orbitals.  Fig. 2 PDOS of d orbitals of Mn at corner site in Mn4-xNixN (x=0, 0.5)