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Publications

A Drift-Diffusion Based Modeling and Optimization Framework for Nanoscale Spin-Orbit Torque Devices

Cornell Affiliated Author(s)
Author
Piyush Kumar
Yu-Ching Liao
Daniel Ralph
Azad Naeemi
Abstract

We present a comprehensive set of experimentally validated/calibrated models that capture the physics of the nanoscale spin-orbit torque (SOT) devices. We consider various effects that are prominent at nanoscale including incomplete current redistribution, interface spin mixing, and nonuniform resistivity that were ignored in the prior modeling efforts. We develop a formalism based on drift-diffusion equations and the transfer matrix method to accurately estimate spin current distribution.

Journal
Institute of Electrical and Electronics Engineers (IEEE)
Date Published

Lorentz electron ptychography for imaging magnetic textures beyond the diffraction limit

Cornell Affiliated Author(s)
Author
Zhen Chen
Emrah Turgut
Yi Jiang
Kayla Nguyen
Matthew Stolt
Song Jin
Daniel Ralph
Gregory Fuchs
David Muller
Abstract

Nanoscale spin textures, especially magnetic skyrmions, have attracted intense interest as candidate high-density and power-efficient information carriers for spintronic devices1,2. Facilitating a deeper understanding of sub-hundred-nanometre to atomic-scale spin textures requires more advanced magnetic imaging techniques3–5. Here we demonstrate a Lorentz electron ptychography method that can enable high-resolution, high-sensitivity magnetic field imaging for widely available electron microscopes.

Journal
Springer Science and Business Media LLC
Date Published
Funding Source
DMR-1719875
DMR-2039380
ECCS-1609585
TEE-D18AC00009

Author Correction: Tilted spin current generated by the collinear antiferromagnet ruthenium dioxide

Cornell Affiliated Author(s)
Author
Arnab Bose
Nathaniel Schreiber
Rakshit Jain
Ding-Fu Shao
Hari Nair
Jiaxin Sun
Xiyue Zhang
David Muller
Evgeny Tsymbal
Darrell Schlom
Daniel Ralph
Abstract

In the version of this article initially published, the title of Fig. 2b was incorrectly shown as “(101) RuO2/Py” where it should have been “(001) RuO2/Py.” An expression in Fig. 3b was incorrectly shown as (Formula presented.) where it should have been (Formula presented.). The changes have been made to the HTML and PDF versions of the article. © The Author(s), under exclusive licence to Springer Nature Limited 2022.

Journal
Springer Science and Business Media LLC
Date Published

Gate-Tunable Anomalous Hall Effect in a 3D Topological Insulator/2D Magnet van der Waals Heterostructure

Cornell Affiliated Author(s)
Author
Vishakha Gupta
Rakshit Jain
Yafei Ren
Xiyue Zhang
Husain Alnaser
Amit Vashist
Vikram Deshpande
David Muller
Di Xiao
Taylor Sparks
Daniel Ralph
Abstract

We demonstrate advantages of samples made by mechanical stacking of exfoliated van der Waals materials for controlling the topological surface state of a three-dimensional topological insulator (TI) via interaction with an adjacent magnet layer. We assemble bilayers with pristine interfaces using exfoliated flakes of the TI BiSbTeSe2and the magnet Cr2Ge2Te6, thereby avoiding problems caused by interdiffusion that can affect interfaces made by top-down deposition methods. The samples exhibit an anomalous Hall effect (AHE) with abrupt hysteretic switching.

Journal
American Chemical Society (ACS)
Date Published
Funding Source
1936383
DMR-2104268
DMR-1719875
NNCI-2025233
FA9550-19-1-0390
CB20-68EO-01

Anisotropic Gigahertz Antiferromagnetic Resonances of the Easy-Axis van der Waals Antiferromagnet CrSBr

Cornell Affiliated Author(s)
Author
Thow Cham
Saba Karimeddiny
Avalon Dismukes
Xavier Roy
Daniel Ralph
Yunqiu Luo
Abstract

We report measurements of antiferromagnetic resonances in the van der Waals easy-axis antiferromagnet CrSBr. The interlayer exchange field and magnetocrystalline anisotropy fields are comparable to laboratory magnetic fields, allowing a rich variety of gigahertz-frequency dynamical modes to be accessed. By mapping the resonance frequencies as a function of the magnitude and angle of applied magnetic field, we identify the different regimes of antiferromagnetic dynamics.

Journal
American Chemical Society (ACS)
Date Published
Funding Source
DMR-1719875
DMR-2104268
NNCI-2025233
DE-SC0019443
FA9550-19-1-0390

Giant bulk spin–orbit torque and efficient electrical switching in single ferrimagnetic FeTb layers with strong perpendicular magnetic anisotropy

Cornell Affiliated Author(s)
Author
Qianbiao Liu
Lijun Zhu
Xiyue Zhang
David Muller
Daniel Ralph
Abstract

Efficient manipulation of antiferromagnetically coupled materials that are integration-friendly and have strong perpendicular magnetic anisotropy (PMA) is of great interest for low-power, fast, dense magnetic storage and computing. Here, we report a distinct, giant bulk damping-like spin-orbit torque in strong-PMA ferrimagnetic Fe100-xTbx single layers that are integration-friendly (composition-uniform, amorphous, and sputter-deposited).

Journal
AIP Publishing
Date Published
Funding Source
DMR-1719875
N00014-19-1-2143
D18AC00009
NNCI-2025233
XDB44000000
201906460052
E2SEBB01

Tilted spin current generated by the collinear antiferromagnet ruthenium dioxide

Cornell Affiliated Author(s)
Author
Arnab Bose
Nathaniel Schreiber
Rakshit Jain
Ding-Fu Shao
Hari Nair
Jiaxin Sun
Xiyue Zhang
David Muller
Evgeny Tsymbal
Darrell Schlom
Daniel Ralph
Abstract

Symmetry plays a central role in determining the polarization of spin currents induced by electric fields. It also influences how these spin currents generate spin-transfer torques in magnetic devices. Here we show that an out-of-plane damping-like torque can be generated in ruthenium dioxide (RuO2)/permalloy devices when the Néel vector of the collinear antiferromagnet RuO2 is canted relative to the sample plane.

Journal
Springer Science and Business Media LLC
Date Published
Funding Source
DE-SC0017671
GBMF9073
2039380
DMR-1719875
DMR-1420645
DMR-1429155
NNCI-2025233

Origin of transverse voltages generated by thermal gradients and electric fields in ferrimagnetic-insulator/heavy-metal bilayers

Cornell Affiliated Author(s)
Author
Arnab Bose
Rakshit Jain
Jackson Bauer
Robert Buhrman
Caroline Ross
Daniel Ralph
Abstract

We compare thermal-gradient-driven transverse voltages in ferrimagnetic-insulator/heavy-metal bilayers (Tm3Fe5O12/W and Tm3Fe5O12/Pt) to corresponding electrically driven transverse resistances at and above room temperature. We find for Tm3Fe5O12/W that the thermal and electrical effects can be explained by a common spin-current detection mechanism, the physics underlying spin Hall magnetoresistance (SMR).

Journal
American Physical Society (APS)
Date Published
Funding Source
DMR-1719875
DE-SC0017671
DMR-1808190
NNCI-2025233
DMR-1419807

Anisotropic Magnon Spin Transport in Ultrathin Spinel Ferrite Thin Films─Evidence for Anisotropy in Exchange Stiffness

Cornell Affiliated Author(s)
Author
Ruofan Li
Peng Li
Di Yi
Lauren Riddiford
Yahong Chai
Yuri Suzuki
Daniel Ralph
Tianxiang Nan
Abstract

Magnon-mediated spin flow in magnetically ordered insulators enables long-distance spin-based information transport with low dissipation. In the materials studied to date, no anisotropy has been observed in the magnon propagation length as a function of propagation direction. Here, we report measurements of magnon spin transport in a spinel ferrite, magnesium aluminum ferrite MgAl0.5Fe1.5O4 (MAFO), which has a substantial in-plane 4-fold magnetic anisotropy.

Journal
American Chemical Society (ACS)
Date Published
Funding Source
NNCI-2025 233
N00014-15-1-0045
FA 9550-20-1-0293
DMR-1719 875
52 073 158,52 161 135 103

Separation of Artifacts from Spin‐Torque Ferromagnetic Resonance Measurements of Spin‐Orbit Torque for the Low‐Symmetry Van der Waals Semi‐Metal ZrTe <sub>3</sub>

Author
Thow Cham
Saba Karimeddiny
Vishakha Gupta
Joseph Mittelstaedt
Daniel Ralph
Abstract

Spin-orbit torques generated by exfoliated layers of the low-symmetry semi-metal ZrTe3 are measured using the spin-torque ferromagnetic resonance (ST-FMR) technique. When the ZrTe3 has a thickness greater than about 10 nm, artifacts due to spin pumping and/or resonant heating can cause the standard ST-FMR analysis to overestimate the true magnitude of the torque efficiency by as much as a factor of 30, and to indicate incorrectly that the spin-orbit torque depends strongly on the ZrTe3 layer thickness.

Journal
Wiley
Date Published
Funding Source
FA9550‐19‐1‐0390
DMR‐1708499
DMR‐1719875
NNCI‐2025233
DE-SC0017671