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Publications

Effects of Anisotropic Strain on Spin-Orbit Torque Produced by the Dirac Nodal Line Semimetal IrO2

Cornell Affiliated Author(s)
Author
Arnab Bose
Jocienne Nelson
Xiyue Zhang
Priyamvada Jadaun
Rakshit Jain
Darrell. Schlom
Daniel. Ralph
David. Muller
Kyle. Shen
Robert Buhrman
Abstract

We report spin-torque ferromagnetic resonance studies of the efficiency of the damping-like (ζDL) spin-orbit torque exerted on an adjacent ferromagnet film by current flowing in epitaxial (001) and (110) IrO2 thin films. IrO2 possesses Dirac nodal lines (DNLs) in the band structure that are gapped by spin-orbit coupling, which could enable a very high spin Hall conductivity, σSH.

Journal
American Chemical Society (ACS)
Date Published
Funding Source
DE-SC0017671
ECCS-1542081
1542081
1709255
1719875
DMR-1539918
DMR-1719875
DMR-1709255
N00014-19-1-2143
Group (Lab)
Kyle Shen Group

Observation of Strong Bulk Damping‐Like Spin‐Orbit Torque in Chemically Disordered Ferromagnetic Single Layers

Cornell Affiliated Author(s)
Author
Lijun Zhu
Xiyue Zhang
David Muller
Daniel Ralph
Robert Buhrman
Abstract

Strong damping-like spin-orbit torque (τDL) has great potential for enabling ultrafast energy-efficient magnetic memories, oscillators, and logic. So far, the reported τDL exerted on a thin-film magnet must result from an externally generated spin current or from an internal non-equilibrium spin polarization in non-centrosymmetric GaMnAs single crystals. Here, for the first time a very strong, unexpected τDL is demonstrated from current flow within ferromagnetic single layers of chemically disordered, face-centered-cubic CoPt.

Journal
Wiley
Date Published
Funding Source
1542081
1719875
ECCS‐1542081
N00014‐15‐1‐2449
DMR‐1719875

Manipulation of the van der Waals Magnet Cr2Ge2Te6 by Spin–Orbit Torques

Author
Vishakha Gupta
Thow Cham
Gregory Stiehl
Arnab Bose
Joseph Mittelstaedt
Kaifei Kang
Shengwei Jiang
Kin Mak
Jie Shan
Robert Buhrman
Daniel Ralph
Abstract

We report measurements of current-induced thermoelectric and spin-orbit torque effects within devices in which multilayers of the semiconducting two-dimensional van der Waals magnet Cr2Ge2Te6 (CGT) are integrated with Pt and Ta metal overlayers. We show that the magnetic orientation of the CGT can be detected accurately either electrically (using an anomalous Hall effect) or optically (using magnetic circular dichroism) with good consistency.

Journal
American Chemical Society (ACS)
Date Published
Funding Source
1719875
2776.047
DMR-1719875
N00014-18-1-2368
NNCI-2025233
DE-SC0017671
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

Direct Visualization of Trimerized States in 1T−TaTe2

Cornell Affiliated Author(s)
Author
Ismail Baggari
Nikhil Sivadas
Gregory Stiehl
Jacob Waelder
Daniel Ralph
Craig Fennie
Lena Kourkoutis
Abstract

Transition-metal dichalcogenides containing tellurium anions show remarkable charge-lattice modulated structures and prominent interlayer character. Using cryogenic scanning transmission electron microscopy (STEM), we map the atomic-scale structures of the high temperature (HT) and low temperature (LT) modulated phases in 1T'-TaTe2. At HT, we directly show in-plane metal distortions which form trimerized clusters and staggered, three-layer stacking.

Journal
American Physical Society (APS)
Date Published
Funding Source
DMR-1539918
DE-SC0017671
NSF-MRI-1429155
1719875
DMR-1719875

Controlling spin current polarization through non-collinear antiferromagnetism

Cornell Affiliated Author(s)
Author
T. Nan
C. Quintela
J. Irwin
G. Gurung
D. Shao
J. Gibbons
N. Campbell
K. Song
S. Choi
L. Guo
R. Johnson
P. Manuel
R. Chopdekar
I. Hallsteinsen
T. Tybell
P. Ryan
J. Kim
Y. Choi
P. Radaelli
D. Ralph
E . Y. Tsymbal
M. Rzchowski
C. Eom
Abstract

The interconversion of charge and spin currents via spin-Hall effect is essential for spintronics. Energy-efficient and deterministic switching of magnetization can be achieved when spin polarizations of these spin currents are collinear with the magnetization. However, symmetry conditions generally restrict spin polarizations to be orthogonal to both the charge and spin flows. Spin polarizations can deviate from such direction in nonmagnetic materials only when the crystalline symmetry is reduced.

Journal
Springer Science and Business Media LLC
Date Published
Funding Source
DMR-1719875
DE-FG02-06ER46327
DMR-1720415
1542081
1708499
1719875
DMR-1629270
FA9550-15-1-0334
W911NF-17-1-0462

Transverse and Longitudinal Spin-Torque Ferromagnetic Resonance for Improved Measurement of Spin-Orbit Torque

Cornell Affiliated Author(s)
Author
Saba Karimeddiny
Joseph Mittelstaedt
Robert Buhrman
Daniel Ralph
Abstract

Spin-torque ferromagnetic resonance (ST-FMR) is a common method used to measure spin-orbit torque (SOT) in heavy-metal/ferromagnet bilayer structures. In the course of a measurement, other resonant processes such as spin pumping (SP) and heating can cause spin-current or heat flows between the layers, inducing additional resonant voltage signals via the inverse spin Hall effect (ISHE) and Nernst effects. In the standard ST-FMR geometry, these extra artifacts exhibit a dependence on the angle of an in-plane magnetic field that is identical to the rectification signal from the SOT.

Journal
American Physical Society (APS)
Date Published
Funding Source
1542081
1708499
1719875
DMR-1708499
DMR-1719875
NNCI-1542081

Spin–orbit torque field-effect transistor (SOTFET): Proposal for a magnetoelectric memory

Cornell Affiliated Author(s)
Author
Xiang Li
Joseph Casamento
Phillip Dang
Zexuan Zhang
Olalekan Afuye
Antonio Mei
Alyssa Apsel
Darrell Schlom
Debdeep Jena
Daniel Ralph
Huili Xing
Abstract

Spin-based memories are attractive for their non-volatility and high durability but provide modest resistance changes, whereas semiconductor logic transistors are capable of providing large resistance changes, but lack memory function with high durability. The recent availability of multiferroic materials provides an opportunity to directly couple the change in spin states of a magnetic memory to a charge change in a semiconductor transistor.

Journal
AIP Publishing
Date Published
Funding Source
ECCS 1740286
1740286

Local Photothermal Control of Phase Transitions for On‐Demand Room‐Temperature Rewritable Magnetic Patterning

Cornell Affiliated Author(s)
Author
Antonio Mei
Isaiah Gray
Yongjian Tang
Jürgen Schubert
Don Werder
Jason Bartell
Daniel Ralph
Gregory Fuchs
Darrell Schlom
Abstract

The ability to make controlled patterns of magnetic structures within a nonmagnetic background is essential for several types of existing and proposed technologies. Such patterns provide the foundation of magnetic memory and logic devices, allow the creation of artificial spin-ice lattices, and enable the study of magnon propagation. Here, a novel approach for magnetic patterning that allows repeated creation and erasure of arbitrary shapes of thin-film ferromagnetic structures is reported.

Journal
Wiley
Date Published
Funding Source
1542081
1719875
1740136
DMR‐1539918
ECCS‐1542081
ECCS‐1740286
2758.001
2758.003
FA9550‐14‐1‐0243
DMR‐1719875

Origin of Strong Two-Magnon Scattering in Heavy-Metal/Ferromagnet/Oxide Heterostructures

Cornell Affiliated Author(s)
Author
Lijun Zhu
Lujun Zhu
D.C. Ralph
Robert Buhrman
Abstract

We experimentally investigate the origin of two-magnon scattering (TMS) in heavy-metal (HM)/ferromagnet (FM)/oxide heterostructures (FM = Co, Ni81Fe19, or Fe60Co20B20) by varying the materials located above and below the FM layer. We show that strong TMS in HM/FM/oxide systems arises primarily at the HM/FM interface and increases with the strength of the interfacial spin-orbit coupling and magnetic roughness at this interface. TMS at the FM/oxide interface is relatively weak, even in systems where spin-orbit coupling at this interface generates strong interfacial magnetic anisotropy.

Journal
American Physical Society (APS)
Date Published
Funding Source
1542081
1719875
ECCS-1542081
N00014-15-1-2449
DMR-1719875
51901121
GK201903024
2019JQ-433

Energy‐Efficient Ultrafast SOT‐MRAMs Based on Low‐Resistivity Spin Hall Metal Au <sub>0.25</sub> Pt <sub>0.75</sub>

Cornell Affiliated Author(s)
Author
Lijun Zhu
Lujun Zhu
Shengjie Shi
Daniel Ralph
Robert Buhrman
Abstract

Many key electronic technologies (e.g., large-scale computing, machine learning, and superconducting electronics) require new memories that are at the same time fast, reliable, energy-efficient, and of low-impedance, which has remained a challenge. Nonvolatile magnetoresistive random access memories (MRAMs) driven by spin–orbit torques (SOTs) have promise to be faster and more energy-efficient than conventional semiconductor and spin-transfer-torque magnetic memories.

Journal
Wiley
Date Published
Funding Source
DMR-1719875
2019JQ-433
1542081
1719875
ECCS-1542081
N00014-15-1-2449
51901121
GK201903024