VIDEO DOI: https://doi.org/10.48448/nz32-qq40

technical paper

MMM 2022

November 07, 2022

Minneapolis, United States

Spin orbit Torques in Magnetron

Weyl semimetals can generate large current-induced spin-orbit torques (SOT) that can manipulate the magnetization dynamics in the ferromagnetic materials, and thus play an important role in spintronic devices. Due to their concomitant reduced symmetries, Weyl semimetals are also promising for generating SOTs with novel symmetries that may be able to switch perpendicular magnetic anisotropy thin films. Recently, the Td phase MoTe2, which is Weyl semimetal, has attracted a lot of attentions in the field of spintronics, due to its theoretically predicted SOT efficiencies that are even larger than those of WTe2 1. Here, we studied the effects of processing conditions on the stoichiometry and crystal structure of the magnetron-sputtered MoTe2 films by using Rutherford backscattering and X-ray diffraction. Furthermore, we identified different phases of the sputtered MoTe2 thin films using Raman spectroscopy, and we have observed a stable Td semimetal phase even at room temperature. The Td phase is generally considered to be a low-temperature phase and only appears at temperatures below 250 K, and at room temperatures, MoTe2 will be in the 1T’ monoclinic phase or the 2H hexagonal phase 2. We have also observed dimensionality-dependent phase transitions from the Td to the 1T’ phase at room temperature for sputtered MoTe2 thin films as the characteristic peak for the Td phase MoTe2 gradually shifts from 264 cm-1 to 259 cm-1(the Raman peak position for the 1T’ phase), as the thickness of the sputtered films increases (shown in Figure 1). Finally, SOT efficiencies of the MoTe2 thin films were measured via spin-torque ferromagnetic resonance (ST-FMR) on MoTe2/Ni80Fe20 heterostructures and we observed a large novel SOT due to the spins with out-of-plane polarization directions in both the symmetric and anti-symmetric components of the homodyne mixing voltage signals (shown in Figure 2). The efficiencies of the novel damping-like and field-like SOT are estimated to be 16% and 27%, respectively.

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