Eric Fullerton1
University of California-San Diego1
Eric Fullerton1
University of California-San Diego1
Topology has emerged in many areas of magnetism that included both chiral spin structures and emergent electronic structures such as Weyl semimetals [1]. The further lowering of the symmetry of the crystal via strain or magnetic order can provide additional functionality. I will discuss recent studies of thin films of candidate Weyl semimetals and their potential use as sources of spin currents in spin-orbit torque devices. Materials studies include ferrimagnetically ordered CrPt<sub>3</sub> [2], antiferromagnetically ordered FeRh [3] and transition metal oxides such IrO<sub>2</sub> [4], CaIrO<sub>3</sub>.and NdNiO<sub>3</sub>. For each we have grown epitaxial chemically ordered films and studied the spin structure, magneto-transport properties, and spin-to-charge conversion that is a source for spin-orbit torques. For CrPt<sub>3</sub> we obtain large anomalous Hall conductivity of 2000 S/cm and large negative magneto-resistance consistent with Weyl semimetal properties. However, this, somewhat surprisingly, does not manifest itself in enhanced charge-to-spin efficiencies. For the antiferromagnetic FeRh phase we observe extremely large, strongly temperature-dependent exotic spin torques with a geometry that is tied to the magnetic ordering direction. Many 5d transition metal oxides such as IrO<sub>2</sub> and CaIrO<sub>3</sub> have unique electronic structures, where the density of states near the Fermi level is dominated by only 5d electrons with strong spin orbit coupling. IrO<sub>2</sub> is one of the simplest of these oxides is a Dirac nodal line semi-metal that exhibits a charge-to-spin conversion that is roughly 8 times larger than that of Pt. I will highlight the potential uses for complex materials that generate large, tunable spin-orbit torques. They may be used in conventional computing to non-volatile memory schemes, or for neuromorphic computing approaches exploiting spin dynamics in more complex magnetic systems. This work is supported by US Department of Energy under Grant No. DE-SC0019273<br/><br/>[1] M. J. Gilbert, Comm. Phys. <b>4</b>, 1-12 (2021).<br/>[2] A. Markou et al., Comm. Phys. <b>4</b>, 104 (2021).<br/>[3] J. Gibbons et al., Phys. Rev. Appl. <b>18</b>, 024075 (2022).<br/>[4] B. Sahoo, A. Frano and E. E. Fullerton, Appl. Phys. Lett. <b>123</b>, 032404 (2023).