Driven gyrotropic skyrmion motion through steps in magnetic anisotropy

Abstract

The discovery of magnetic skyrmions in ultrathin heterostructures has led to great interest in possible applications in memory and logic devices. The non-trivial topology of magnetic skyrmions gives rise to a gyrotropic motion, where, under an applied energy gradient a skyrmion gains a component of motion perpendicular to the applied force. So far, device proposals have largely neglected this motion or treated it as a barrier to correct operation. Here, we show that skyrmions can be efficiently moved perpendicular to an energy step created by local changes in the perpendicular magnetic anisotropy. We propose an experimentally-realizable skyrmion racetrack device which uses voltage-controlled magnetic anisotropy to induce a step in magnetic anisotropy and drive a skyrmion unidirectionally using alternating voltage pulses.

Reverse‐Engineering Strain in Nanocrystallites by Tracking Trimerons

“…XRD patterns were acquired in a Bruker D8 Advance diffractometer with Cu Kα using a room temperature rotation stage and an Oxford Cryosystems PheniX closed cycle refrigeration system stage at 20-300 K. Patterns were refined using GSAS II. [66] Mössbauer spectra were collected from 10 to 300 K using a Janis SHI-850 closed cycle refrigeration system and a WissEl constant acceleration spectrometer with a 100 MBq 57 CoRh source. The source drive velocity was calibrated using 6 μm α-Fe foil at room temperature.…”

“…Since the low temperature monoclinic phase is established by the freezing of phonon modes, [6,15] we can use the measured relative absorption (f-factor, or Debye-Waller factor) of Mössbauer spectra to detect the structural transition. The relative absorption of a spectrum depends on the oxidation and spin state of the 57 Fe atoms in the nanocrystals, as well as the "elastic bond" strength-therefore, a temperature-dependent valence change, change in spin state, or phase change may be easily detected. For the Verwey transition, it is expected that as more phonon modes become accessible, the f-factor will increase with cooling, thus the transition from Fe 3 O 4 's high temperature cubic phase to low temperature monoclinic phase corresponds to an increase in f-factor, show as a step or kink in f(T).…”

“…Orbital moments of electrons have been quite challenging to control, but they offer greater adjustability with respect to magnitude and internal structure (compared to spin), and the orbital moment is key to novel and promising effects such as the gyrotropic magnetic [56,57] and orbital Rashba-Edelstein effects. [55,58] Consider that access to strain in nanoscale transition metal oxides offers a practical way to tune the spin and orbital magnetism necessary for orbitronic circuits.…”

Skyrmion battery effect via inhomogeneous magnetic anisotropy

“…Inhomogeneity in magnetic anisotropy also exerts impact on the motion of skyrmions. In the presence of a carefully patterned anisotropy gradient [50][51][52] , a skyrmion driven by a voltage pulse can travel more than 500nm. An interlayer coupling in a synthetic antiferromagnetic bilayer structure with an anisotropy gradient can further enhance the skyrmion velocity 53 .…”

Thermal motion of skyrmion arrays in granular films

“…This means that the grain boundaries act as local anisotropy steps. It has been previously shown that anisotropy steps are capable of producing an effective force on a single skyrmion [41], with implications for devices. The step in uniaxial anisotropy due to the underlying grains can be incorporated into the Thiele equation as an effective force similar to an energy gradient, by defining the skyrmion energy due to the uniaxial anisotropy E K u .…”