Voltage-Controlled Dzyaloshinskii-Moriya Interaction Torque Switching of Perpendicular Magnetization.

Magnetization switching is the most important operation in spintronic devices. In modern nonvolatile magnetic random-access memory (MRAM), it is usually realized by spin-transfer torque (STT) or spin-orbit torque (SOT). However, both STT and SOT MRAM require current to drive magnetization switching, which will cause Joule heating. Here, we report an alternative mechanism, Dzyaloshinskii-Moriya interaction (DMI) torque, that can realize magnetization switching fully controlled by voltage pulses. We find that a consequential voltage-controlled reversal of DMI chirality in multiferroics can lead to continued expansion of a skyrmion thanks to the DMI torque. Enough DMI torque will eventually make the skyrmion burst into a quasiuniform ferromagnetic state with reversed magnetization, thus realizing the switching of a perpendicular magnet. The discovery is demonstrated in two-dimensional multiferroics, CuCrP_{2}Se_{6} and CrN, using first-principles calculations and micromagnetic simulations. As an example, we applied the DMI torque for simulating leaky-integrate-fire functionality of biological neurons. Our discovery of DMI torque switching of perpendicular magnetization provides tremendous potential toward magnetic-field-free and current-free spintronic devices, and neuromorphic computing as well.

Anisotropic Dzyaloshinskii-Moriya Interaction and Topological Magnetism in Two-Dimensional Magnets Protected by P4Ì m2 Crystal Symmetry.

As a fundamental magnetic parameter, Dzyaloshinskii-Moriya interaction (DMI), has gained a great deal of attention in the last two decades due to its critical role in formation of magnetic skyrmions. Recent discoveries of two-dimensional (2D) van der Waals (vdW) magnets has also gained a great deal of attention due to appealing physical properties, such as gate tunability, flexibility, and miniaturization. Intensive studies have shown that isotropic DMI stabilizes ferromagnetic (FM) topological spin textures in 2D magnets or their corresponding heterostructures. However, the investigation of anisotropic DMI and antiferromagnetic (AFM) topological spin configurations remains elusive. Here, we propose and demonstrate a family of 2D magnets with P4m2 symmetry-protected anisotropic DMI. More interestingly, various topological spin configurations, including FM/AFM antiskyrmion and AFM vortex-antivortex pair, emerge in this family. These results give a general method to design anisotropic DMI and pave the way toward topological magnetism in 2D materials using crystal symmetry.

Syntropic spin alignment at the interface between ferromagnetic and superconducting nitrides.

The magnetic correlations at the superconductor/ferromagnet (S/F) interfaces play a crucial role in realizing dissipation-less spin-based logic and memory technologies, such as triplet-supercurrent spin-valves and 'π' Josephson junctions. Here we report the observation of an induced large magnetic moment at high-quality nitride S/F interfaces. Using polarized neutron reflectometry and DC SQUID measurements, we quantitatively determined the magnetization profile of the S/F bilayer and confirmed that the induced magnetic moment in the adjacent superconductor only exists below T C. Interestingly, the direction of the induced moment in the superconductors was unexpectedly parallel to that in the ferromagnet, which contrasts with earlier findings in S/F heterostructures based on metals or oxides. First-principles calculations verified that the unusual interfacial spin texture observed in our study was caused by the Heisenberg direct exchange coupling with constant J∼4.28 meV through d-orbital overlapping and severe charge transfer across the interfaces. Our work establishes an incisive experimental probe for understanding the magnetic proximity behavior at S/F interfaces and provides a prototype epitaxial 'building block' for superconducting spintronics.

Hole doping induced ferromagnetism and Dzyaloshinskii-Moriya interaction in the two-dimensional group-IVA oxides.

Based on the first-principles calculations, we examine the effect of hole doping on the ferromagnetism and Dzyaloshinskii-Moriya interaction (DMI) for PbSnO2, SnO2and GeO2monolayers. The nonmagnetic to ferromagnetic transition and the DMI can emerge simultaneously in the three two-dimensional IVA oxides. By increasing the hole doping concentration, we find the ferromagnetism can be strengthened for the three oxides. Due to different inversion symmetry breaking, isotropic DMI is found in PbSnO2, whereas anisotropic DMI presents in SnO2and GeO2. More appealingly, for PbSnO2with different hole concentrations, DMI can induce a variety of topological spin textures. Interestingly, a peculiar feature of synchronously switch of magnetic easy axis and DMI chirality upon hole doping is found in PbSnO2. Hence, Néel-type skyrmions can be tailored via changing hole density in PbSnO2. Furthermore, we demonstrate that both SnO2and GeO2.with different hole concentrations can host antiskyrmions or antibimerons (in-plane antiskyrmions). Our findings demonstrate the presence and tunability of topological chiral structures in p-type magnets and open up new possibility for spintronics.