Magnetization switching in polycrystalline Mn3Sn thin film induced by self-generated spin-polarized current

Abstract

Electrical manipulation of spins is essential to design state-of-the-art spintronic devices and commonly relies on the spin current injected from a second heavy-metal material. The fact that chiral antiferromagnets produce spin current inspires us to explore the magnetization switching of chiral spins using self-generated spin torque. Here, we demonstrate the electric switching of noncollinear antiferromagnetic state in Mn3Sn by observing a crossover from conventional spin-orbit torque to the self-generated spin torque when increasing the MgO thickness in Ta/MgO/Mn3Sn polycrystalline films. The spin current injection from the Ta layer can be controlled and even blocked by varying the MgO thickness, but the switching sustains even at a large MgO thickness. Furthermore, the switching polarity reverses when the MgO thickness exceeds around 3 nm, which cannot be explained by the spin-orbit torque scenario due to spin current injection from the Ta layer. Evident current-induced switching is also observed in MgO/Mn3Sn and Ti/Mn3Sn bilayers, where external injection of spin Hall current to Mn3Sn is negligible. The inter-grain spin-transfer torque induced by spin-polarized current explains the experimental observations. Our findings provide an alternative pathway for electrical manipulation of non-collinear antiferromagnetic state without resorting to the conventional bilayer structure.

Nanoscale Magnetic Domains in Polycrystalline Mn3Sn Films Imaged by a Scanning Single-Spin Magnetometer

“…In addition to the static magnetic field, current-induced spin–orbit torques (SOTs) can also be used to achieve efficient control of the local spin orders of Mn 3 Sn. − , Next, we utilize our scanning NV microscope to reveal evolutions of the measured stray field patterns during electrically driven perpendicular magnetic switching of Mn 3 Sn. For these measurements, we prepared Mn 3 Sn (70 nm)/W (7 nm) bilayer samples and patterned them to standard Hall cross devices for magneto-transport characterizations as shown in the left panel of Figure a.…”

“…For these measurements, we prepared Mn 3 Sn (70 nm)/W (7 nm) bilayer samples and patterned them to standard Hall cross devices for magneto-transport characterizations as shown in the left panel of Figure a. The W capping layer serves as an efficient source of spin–orbit torques (SOTs) , for driving the magnetic switching in Mn 3 Sn, arguably together with other potential contributions such as local heating effects and intergrain spin transfer torques. − Current driven magnetic switching measurements follow the standard procedure as reported in the previous literature. , Electrical write current pulses I write are applied through the current channel of a patterned Hall cross device, generating transverse spin currents through spin Hall effect in the W layer, assuming the diffusive picture of spin transport is valid and spin currents are approximately well-defined. The spin current then flows across the heterostructure interface and exerts SOTs on the local magnetic moments in Mn 3 Sn, resulting in reversible switching of the canted ferromagnetic moment with the assistance of a longitudinal bias field (see Supporting Information Section 5 for details).…”

“…Harnessing magnetic domain motions for advanced information processing, transfer, and storage constitutes a key mission of modern spintronic technologies. − Over the past decade, (ferri)­ferromagnetic materials with net magnetization, robust stray field patterns, and prominent magneto-transport responses naturally played a leading role in this contest, and a variety of cutting-edge spintronic devices have been developed along this direction. − More recently, antiferromagnets featuring vanishingly small net magnetization and exchange-enhanced magnetic interactions emerge as a new contender of this field. , Novel functionalities such as ultrahigh-density magnetic memory, improved stability, , and unconventional magnetic switching strategies − are under intensive investigation for developing next-generation, transformative micromagnetic devices. The family of noncollinear antiferromagnets Mn 3 X (X = Sn, Ge, Ga, Ir, Pt, Rh) are naturally relevant in this context, owing to their emergent electronic and magnetic structures.…”

“…An apparent stumbling block results from the nearly compensated magnetization, which is difficult to access by existing magnetometry techniques. While previous work has reported visualization of magnetic domains of Mn 3 Sn using magneto-optic Kerr effect microscopy, , the spatial resolution is fundamentally constrained by the optical diffraction limit and is constrained to the micrometer length scale. Thus, a clear picture of the microscopic magnetic textures at the nanoscale remains elusive.…”

“…Figure h shows schematics of the local magnetic order of a prepared Mn 3 Sn film after training with a large positive (negative) perpendicular magnetic field. Polycrystalline Mn 3 Sn samples consist of weakly coupled magnetic grains with dominantly in-plane and out-of-plane oriented kagome planes. , When reversing the sign of the external perpendicular magnetic field, magnetic grains with out-of-plane oriented kagome planes switch accordingly to follow the external field direction. Similarly, grains with their kagome planes nearly parallel to the film can also be switched by the perpendicular magnetic field, as long as the projection of the magnetic field into the kagome plane of a given grain is larger than its coercive field.…”