Session C01: Parallel Invited Session - Condensed Matter I

A new spin on magnetism with applications in information processing

Recent advances in magnetism research are likely to have an important impact on electronics and information processing. These advances use the electron’s magnetic moment (spin) to transmit, write and store information. They enable new devices that operate at high speed with very low energy consumption. The information is stored in the orientation of electron magnetic moments in magnetic materials and can persist without power; energy is only needed to write and read the information. Important physics concepts include the interconversion of electrical (charge) currents into spin currents, the efficiency of the interconversion, controlling the currents’ spin polarization direction and the associated spin torques on magnetic order. In this talk I will highlight the new physics concepts that have enabled these advances and discuss some of their applications in information processing. I plan to present my group's studies of current-induced switching of magnetization in magnetic tunnel junction nanopillars. This includes our recent experimental studies that demonstrate that the stochastic nature of the switching can be used to generate truly random numbers at GHz rates in devices that are very attractive for applications, such as for cryptography and Monte Carlo simulations [1]. I will also show that currents can exert torques that affect order in an insulating antiferromagnet α-Fe₂O₃ [2,3], materials that are interesting because of their even higher (THz) frequency spin dynamics.

    

Spin Torque Control of Magnetic Multiples in Topological Antiferromagnets

Electrical manipulation of spin textures inside antiferromagnets represents a new opportunity for developing spintronics with superior speed and high device density. Different from ferromagnet where the magnetic ordering is described by a magnetic dipole moment, the magnetic ordering in antiferromagnet needs to be characterized by higher order magnetic multipole moment like quadrupoles or octupoles. It remains an interesting question how to  realize efficient control of the magnetic multipoles through the spin torque effect, which in nature reflects the transfer of dipolar angular momentum. In some of the existing reports on antiferromagnetic switching, because of the diminishing magnetic susceptibility, the nature and the magnitude of current-induced magnetic dynamics remain poorly characterized, whereas spurious effects further complicate experimental interpretations [1].

In this talk, I will discuss our recent experimental studies on controlling magnetic multipoles of antiferromagnets using spin orbit torque. First, by growing a thin film antiferromagnetic insulator, α-Fe₂O₃, along its non-basal plane orientation, we realize a configuration where an injected spin current can robustly rotate the quadrupole moment – the Neel vector within the tilted easy plane, with an efficiency comparable to that of classical ferromagnets [2]. Secondly, we also studied the spin torque induced magnetic dynamics in a non-collinear topological antiferromagnetic semimetal, where the spin orbit torque induces distinct dynamics on magnetic octupole moment compared with the well known magnetization dynamics in regular ferromagnets. By enabling efficient spin-orbit torque control on the antiferromagnetic ordering, our studies introduce new platforms for quantitatively understanding switching and oscillation dynamics in antiferromagnets.