Field-free spin-orbit torque switching of GdCo ferrimagnet with broken lateral symmetry by He ion irradiation

Current-induced magnetization switching by spin-orbit torque (SOT) is of great importance for the energy-efficient operation of spin-based memory and logic devices. However, the requirement of an external in-plane magnetic field to deterministically switch the perpendicular magnetization of a device is a bottleneck for device application. There have been many efforts to realize field-free SOT switching using interlayer/exchange coupling, the spin valve structure, or materials with lateral symmetry breaking. However, limitations of material selection or layer structure modification hinder the application of these methods in practice. Here, we demonstrate the field-free SOT switching of a GdCo ferrimagnet with lateral symmetry breaking by He ion irradiation. Local control of the magnetic property with different He ion irradiation conditions induces a lateral magnetic gradient orthogonal to the current flow direction in the ferrimagnet. We also observe out-of-plane-SOT generation due to lateral symmetry breaking, which is essential for field-free switching. Since the He ion irradiation technique is utilized for the fabrication of complementary−metal−oxide−semiconductors, and resolution can reach the nanometer level, our findings have the potential to serve as the basis for new developments in the fabrication of wafer-scale spintronic memory and logic devices with high energy efficiency and high density. © 2023 Acta Materialia Inc.FALS

Freestanding Oxide Membranes for Epitaxial Ferroelectric Heterojunctions

Since facile routes to fabricate freestanding oxide membraneswerepreviously established, tremendous efforts have been made to furtherimprove their crystallinity, and fascinating physical properties havebeen also reported in heterointegrated freestanding membranes. Here,we demonstrate our synthetic recipe to manufacture highly crystallineperovskite SrRuO3 freestanding membranes using new infinite-layerperovskite SrCuO2 sacrificial layers. To accomplish this,SrRuO3/SrCuO2 bilayer thin films are epitaxiallygrown on SrTiO3 (001) substrates, and the topmost SrRuO3 layer is chemically exfoliated by etching the SrCuO2 template layer. The as-exfoliated SrRuO3 membranes aremechanically transferred to various nonoxide substrates for the subsequentBaTiO(3) film growth. Finally, freestanding heteroepitaxialjunctions of ferroelectric BaTiO3 and metallic SrRuO3 are realized, exhibiting robust ferroelectricity. Intriguingly,the enhancement of piezoelectric responses is identified in freestandingBaTiO(3)/SrRuO3 heterojunctions with mixed ferroelectricdomain states. Our approaches will offer more opportunities to developheteroepitaxial freestanding oxide membranes with high crystallinityand enhanced functionality

Unidirectional spin Hall magnetoresistance in epitaxial Cr/Fe bilayer from electron-magnon scattering

Unidirectional Spin Hall magnetoresistance (USMR) is a non-linear phenomenon recently observed in ferromagnet (FM)/nonmagnetic metal (NM) bilayer structures. Two very different mechanisms of USMR have been proposed; one relies on the current-direction-dependence of electron-magnon scattering in a FM layer, and the other on the current-direction-dependence of the spin accumulation at the FM/NM interface. In this study, we investigate the USMR in epitaxial Cr/Fe bilayers finding that the USMR is significantly enhanced when the Fe magnetization is aligned to a particular crystallographic direction where the magnon magnetoresistance (MMR) by the electron-magnon scattering becomes stronger. This highlights the importance of the electron-magnon scattering for the understanding of USMR in Cr/Fe bilayers. Our result also suggests a route to enhance the efficiency of magnon generation in the magnonic devices. Lastly, we discuss the Ising-type spin exchange as a possible origin of the crystallographic direction dependences of the USMR and the MMR. Unidirectional spin Hall magnetoresistance (USMR) is a directionally dependent feature of a ferromagnetic/normal metal bilayer for which the underlying mechanisms are still under debate. Here, the authors investigate the crystallographic dependence of USMR in epitaxial Cr/Fe bilayers finding that electron-magnon scattering plays an important role.11Nsciescopu