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6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Unconventional fieldlike spin torques in CrPt 3

The topological semimetal CrPt 3 has potential for generating unconventional spin torques due to its ferrimagnetic ordering, topological band structure, and high anomalous Hall effect. CrPt 3 exhibits ferrimagnetic behavior only in its chemically ordered phase and is paramagnetic in its chemically disordered phase. By controlling the growth and annealing temperatures, we prepare epitaxial films of both chemically ordered and chemically disordered phases of CrPt 3 , allowing us to investigate the effect of magnetic ordering on unconventional-torque generation. We use angle-dependent spin-torque-ferromagnetic-resonance and second-harmonic Hall measurements to probe the spin torques generated from epitaxial CrPt 3 in CrPt 3 /Cu/Ni 81 ⁢Fe 19 heterostructures. With current applied along specific directions with respect to the crystal order, we reveal unconventional spin torques in both ordered and disordered films. When current flows parallel to the [$1\bar{1}1$] and [ $\bar{1}11$] directions, we observe an unconventional fieldlike torque that is opposite in sign for the two directions. Finally, our calculations reveal that this unconventional torque originates from an indirect nonlocal spin-orbit torque due to spin scattering at the CrPt 3 /Cu interface, in addition to symmetry breaking at this interface.

ferromagnetic resonance↗
DOE OSTI2020

Materials Data on CrPt(NCl)5 by Materials Project

CrPt(NCl)5 is beta Np structured and crystallizes in the orthorhombic Pnma space group. The structure is zero-dimensional and consists of four CrPt(NCl)5 clusters. Cr6+ is bonded in a 2-coordinate geometry to four N+1.40- and one Cl1- atom. There is two shorter (1.61 Å) and two longer (2.29 Å) Cr–N bond length. The Cr–Cl bond length is 2.16 Å. Pt6+ is bonded in a rectangular see-saw-like geometry to four Cl1- atoms. There are two shorter (2.26 Å) and two longer (2.27 Å) Pt–Cl bond lengths. There are three inequivalent N+1.40- sites. In the first N+1.40- site, N+1.40- is bonded in a single-bond geometry to one Cr6+ atom. In the second N+1.40- site, N+1.40- is bonded in a 2-coordinate geometry to one Cr6+ and one N+1.40- atom. The N–N bond length is 1.30 Å. In the third N+1.40- site, N+1.40- is bonded in a 3-coordinate geometry to two equivalent N+1.40- and one Cl1- atom. The N–Cl bond length is 3.15 Å. There are four inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a distorted single-bond geometry to one Pt6+ atom. In the second Cl1- site, Cl1- is bonded in a single-bond geometry to one Pt6+ atom. In the third Cl1- site, Cl1- is bonded in a single-bond geometry to one Cr6+ atom. In the fourth Cl1- site, Cl1- is bonded in a single-bond geometry to one Pt6+ and one N+1.40- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CrPt by Materials Project

PtCr is Tetraauricupride structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. Cr2+ is bonded in a 8-coordinate geometry to eight equivalent Pt2- atoms. All Cr–Pt bond lengths are 2.70 Å. Pt2- is bonded to eight equivalent Cr2+ and four equivalent Pt2- atoms to form a mixture of distorted corner, edge, and face-sharing PtCr8Pt4 cuboctahedra. All Pt–Pt bond lengths are 2.67 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CrPt by Materials Project

PtCr crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are three inequivalent Cr2+ sites. In the first Cr2+ site, Cr2+ is bonded in a distorted hexagonal planar geometry to six equivalent Pt2- atoms. All Cr–Pt bond lengths are 2.68 Å. In the second Cr2+ site, Cr2+ is bonded in a distorted hexagonal planar geometry to six Pt2- atoms. All Cr–Pt bond lengths are 2.68 Å. In the third Cr2+ site, Cr2+ is bonded in a distorted hexagonal planar geometry to six Pt2- atoms. All Cr–Pt bond lengths are 2.68 Å. There are two inequivalent Pt2- sites. In the first Pt2- site, Pt2- is bonded to six Cr2+ and six equivalent Pt2- atoms to form a mixture of distorted edge, corner, and face-sharing PtCr6Pt6 cuboctahedra. All Pt–Pt bond lengths are 2.71 Å. In the second Pt2- site, Pt2- is bonded to six Cr2+ and ten equivalent Pt2- atoms to form distorted PtCr6Pt10 cuboctahedra that share corners with twelve PtCr6Pt6 cuboctahedra, edges with sixteen PtCr6Pt6 cuboctahedra, and faces with sixteen equivalent PtCr6Pt10 cuboctahedra. There are a spread of Pt–Pt bond distances ranging from 2.71–5.41 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2023

High-temperature ferromagnetism in Cr 1+x Pt 5-x P

In this work, we present the growth and basic magnetic and transport properties of Cr 1+x Pt 5-x P. We show that single crystals can readily be grown from a high-temperature solution created by adding dilute quantities of Cr to Pt-P based melts. Like other 1-5-1 compounds, Cr 1+x Pt 5-x P adopts a tetragonal P4/mmm, structure composed facesharing CrPts like slabs that are broken up along the c-axis by sheets of P atoms. EDS and X-ray diffraction measurements both suggest Cr 1+x Pt 5-x P has mixed occupancy between Cr and Pt atoms, similar to what is found in the closely related compound CrPtg, giving real compositions of Cr 1.5 Pt 4.5 P (x = 0.5). We report that Cr 1.5 Pt 4.5 P orders ferromagnetically at T c = 464.5 K with a saturated moment of ≈ 2.1 μs/Cr at 1.8 K. Likely owing to the strong spin-orbit coupling associated with the large quantity of high Z, Pt atoms, Cr 1.5 Pt 4.5 P has exceptionally strong planar anisotropy with estimated anisotropy fields of 345 kOe and 220 kOe at 1.8 K and 300 K respectively. The resistance of Cr 1.5 Pt 4.5 P has a metallic temperature dependence with relatively weak magnetoresistance. Electronic band structure calculations show that CrPt 5 P has a large peak in the density of states near the Fermi level which is split into spin majority and minority bands in the ferromagnetic state. Furthermore, the calculations suggest substantial hybridization between Cr-3d and Pt-5d states near the Fermi level, in agreement with the experimentally measured anisotropy.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Unconventional Spin-Orbit Torques Due to Reduced Crystal Symmetries

Spin-orbit torques have emerged as a powerful mechanism for manipulating magnetic moments in spintronic devices, offering a pathway to more efficient and scalable memory and logic technologies. While conventional spin-orbit torques generated in heavy metals and topological insulators have been extensively studied, recent advancements in unconventional spin-orbit torques demonstrated out-of-plane spin polarizations that could effectively switch perpendicular magnetizations without the need for additional external in-plane magnetic fields, promising significant implications for the development of energy-efficient and compact spintronic devices. Unconventional spin-orbit torques are usually found in materials with low symmetries, such as transition metal dichalcogenides, topological insulators, and 2-D materials. Here, we provide a brief overview of unconventional spin-orbit torques and present two example material systems: CrPt 3 and MoTe 2 , both exhibiting strong spin-orbit coupling and phase-dependent spin-orbit torques, and focus on their unique origins and potential applications. We discuss the roles of magnetic and crystallographic orders in generating unconventional spin-orbit torques, highlighting how these factors contribute to the observed anisotropic and directional dependencies.

magnetic films↗