First-principles spin-transfer torque in CuMnAs|GaP|CuMnAs junctions

Abstract

We demonstrate that an all-antiferromagnetic tunnel junction with current perpendicular to the plane geometry can be used as an efficient spintronic device with potential high-frequency operation. By using state-of-the-art density functional theory combined with quantum transport, we show that the Néel vector of the electrodes can be manipulated by spin-transfer torque. This is staggered over the two different magnetic sublattices and can generate dynamics and switching. At the same time the different magnetization states of the junction can be read by standard tunneling magnetoresistance. Calculations are performed for CuMnAs|GaP|CuMnAs junctions with different surface terminations between the antiferromagnetic CuMnAs electrodes and the insulating GaP spacer. We find that the torque remains staggered regardless of the termination, while the magnetoresistance depends on the microscopic details of the interface. DOI: 10.1103/PhysRevB.95.060403Antiferromagnetic (AF) materials are magnetically ordered compounds where two or more spin sublattices compensate each other, resulting in a vanishing macroscopic magnetization. As a consequence, an antiferromagnet does not produce stray field, and closely separated AF nanostructures are not magnetostatically coupled. In addition, the typical time scale for the dynamics of the antiferromagnetic order parameter, the Néel vector, is set by the AF resonance frequency, which is typically much larger than that of a ferromagnet, and may approach the THz range [1]. It is then not surprising that antiferromagnets have recently received considerable attention as a materials platform for magnetic data storage, logic, and high-frequency applications [2]. One limitation of the AF materials class is the fact that most antiferromagnets are insulators, while often spintronics devices require driving currents through the structure.Recently, metallic CuMnAs has been proposed as a good candidate for AF spintronics applications [3]. Tetragonal CuMnAs is antiferromagnetic at room temperature and can be grown epitaxially on GaP. Furthermore, it has been shown that one can manipulate the Néel vector of CuMnAs thin films by electric current pulses [4]. This is explained as the result of atomically staggered spin-orbit torques (SOTs), 1 which accompany the current flow in antiferromagnets where the global inversion symmetry is broken due to the presence of two spin sublattices forming inversion partners [5]. The reported Néel temperature of CuMnAs is (480 ± 5) K [6], while the lattice parameters of bulk tetragonal CuMnAs are a = b = 3.820Å and c = 6.318Å. According to density functional theory (DFT) calculations, CuMnAs in its AF ground state is metallic, but it has a rather low density of states at the Fermi level [3]. Here, we investigate whether such a unique AF metal can be used in standard magnetic tunnel junctions (MTJs) and demonstrate that these can be written by spin-transfer torques (STTs) and read by standard tunnel magnetoresistance (TMR). * stamenom@tcd.ie 1 These are also referred to ...

Spin and Charge Pumping by a Steady or Pulse-Current-Driven Magnetic Domain Wall: A Self-Consistent Multiscale Time-Dependent Quantum-Classical Hybrid Approach

“…The theoretical analysis of these phenomena requires to account for the interaction of fast conduction electrons, described quantum-mechanically, with slow magnetic moments whose dynamics can be captured by the * bnikolic@udel.edu † Present Address: Catalan Institute of Nanoscience and Nanotechnology (ICN2), Campus UAB, Bellaterra, 08193 Barcelona, Spain classical Landau-Lifshitz-Gilbert (LLG) equation [3,20,21]. However, quantum transport studies of spin torque in spin-valves [16,[22][23][24], MTJs [25][26][27] and DWs [28][29][30][31][32][33][34] are typically confined to computing torque of steady current of electrons acting on a chosen static configuration of localized magnetic moments. Similarly, standard simulations of current-driven magnetization dynamics [2,3] or motion of DWs [7,8,21,[35][36][37][38][39][40][41] and skyrmions [42,43] evade explicit modeling of the flow of conduction electrons by using only classical micromagnetics into which one has to introduce phenomenological terms to describe the so-called adiabatic (when propagating electron spins remain mostly aligned or antialigned with the localized magnetic moments) and nonadiabatic (which can have local [28][29][30] and nonlocal [31][32][33] contributions) spin torques due to flowing electrons.…”

Multiscale modeling of current-induced switching in magnetic tunnel junctions using ab initio spin-transfer torques

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