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Publications

Imaging uncompensated moments and exchange-biased emergent ferromagnetism in FeRh thin films

Cornell Affiliated Author(s)
Author
Isaiah Gray
Gregory Stiehl
John Heron
Antonio Mei
Darrell Schlom
Ramamoorthy Ramesh
Daniel Ralph
Gregory Fuchs
Abstract

Uncompensated moments (UMs) in antiferromagnets are responsible for exchange bias in antiferromagnet/ ferromagnet heterostructures; however, they are difficult to directly detect because any signal they contribute is typically overwhelmed by the ferromagnetic layer. We use magnetothermal microscopy to image micron-scale uncompensated moments in thin films of FeRh, a room-temperature antiferromagnet that exhibits a first-order phase transition to a ferromagnetic (FM) state near 400 K.

Journal
American Physical Society (APS)
Date Published
Funding Source
1542081
1708499
1719875
1740136
SRC

Materials Relevant to Realizing a Field-Effect Transistor Based on Spin–Orbit Torques

Cornell Affiliated Author(s)
Author
Phillip Dang
Zexuan Zhang
Joseph Casamento
Xiang Li
Jashan Singhal
Darrell Schlom
Daniel Ralph
Huili Xing
Debdeep Jena
Abstract

Spin-orbit torque (SOT) is a promising mechanism for writing magnetic memories, while field-effect transistors (FETs) are the gold-standard device for logic operation. The spin-orbit torque field-effect transistor (SOTFET) is a proposed device that couples an SOT-controlled ferromagnet to a semiconducting transistor channel via the transduction in a magnetoelectric multiferroic (MF). This allows the SOTFET to operate as both a memory and a logic device, but its realization depends on the choice of appropriate materials.

Journal
Institute of Electrical and Electronics Engineers (IEEE)
Date Published
Funding Source
E2CDA 1740286
NewLAW EFRI 1741694
DGE-1650441
1740286
1741694

Modeling and Circuit Design of Associative Memories With Spin–Orbit Torque FETs

Cornell Affiliated Author(s)
Author
Olalekan Afuye
Xiang Li
Felicia Guo
Debdeep Jena
Daniel Ralph
Alyosha Molnar
Huili Xing
Alyssa Apsel
Abstract

This article introduces a circuits model for a proposed spin-based device called a spin-orbit torque field-effect transistor (SOTFET) that can operate as a nonvolatile memory and logic device. The SOTFET utilizes an FET structure with a ferromagnetic-multiferroic (MF) gate-stack that enables read/compute and write functions to be isolated. This is achieved by a combination of a ferromagnetic layer that is programmable via spin-orbit torque coupled to an MF layer that also couples into the gate of a traditional FET.

Journal
Institute of Electrical and Electronics Engineers (IEEE)
Date Published
Funding Source
1740286
ECCS 1740286
2758.001
2758.002

Ferroelectric properties of ion-irradiated bismuth ferrite layers grown via molecular-beam epitaxy

Cornell Affiliated Author(s)
Author
Antonio Mei
Sahar Saremi
Ludi Miao
Matthew Barone
Yongjian Tang
Cyrus Zeledon
Jürgen Schubert
Daniel Ralph
Lane Martin
Darrell Schlom
Abstract

We systematically investigate the role of defects, introduced by varying synthesis conditions and by carrying out ion irradiation treatments, on the structural and ferroelectric properties of commensurately strained bismuth ferrite BixFe2-xO3 layers grown on SrRuO3-coated DyScO3(110)o substrates using adsorption-controlled ozone molecular-beam epitaxy. Our findings highlight ion irradiation as an effective approach for reducing through-layer electrical leakage, a necessary condition for the development of reliable ferroelectrics-based electronics. © 2019 Author(s).

Journal
AIP Publishing
Date Published
Funding Source
1708615
1719875
1740286
SRC

Layer-dependent spin-orbit torques generated by the centrosymmetric transition metal dichalcogenide β−MoTe2

Cornell Affiliated Author(s)
Author
Gregory Stiehl
Ruofan Li
Vishakha Gupta
Ismail Baggari
Shengwei Jiang
Hongchao Xie
Lena Kourkoutis
Kin Mak
Jie Shan
Robert Buhrman
Daniel Ralph
Abstract

Single-crystal materials with sufficiently low crystal symmetry and strong spin-orbit interactions can be used to generate novel forms of spin-orbit torques on adjacent ferromagnets, such as the out-of-plane antidamping torque previously observed in WTe2/ferromagnet heterostructures. Here, we present measurements of spin-orbit torques produced by the low-symmetry material β-MoTe2, which, unlike WTe2, retains bulk inversion symmetry.

Journal
American Physical Society (APS)
Date Published
Funding Source
1429155
1542081
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

MoS2 pixel arrays for real-time photoluminescence imaging of redox molecules

Cornell Affiliated Author(s)
Author
M.F. Reynolds
M.H.D. Guimarães
H. Gao
K. Kang
A.J. Cortese
D.C. Ralph
J. Park
P.L. McEuen
Abstract

Measuring the behavior of redox-active molecules in space and time is crucial for understanding chemical and biological systems and for developing new technologies. Optical schemes are noninvasive and scalable, but usually have a slow response compared to electrical detection methods. Furthermore, many fluorescent molecules for redox detection degrade in brightness over long exposure times. Here, we show that the photoluminescence of “pixel” arrays of monolayer MoS2 can image spatial and temporal changes in redox molecule concentration.

Journal
Science Advances
Date Published
Funding Source
ECCS-1542081
NSF DMR-1420709
DMR-1719875
FA9550-16-1-0031
680-50-1311
Group (Lab)
Paul McEuen Group

Spin Seebeck Imaging of Spin-Torque Switching in Antiferromagnetic Pt/NiO Heterostructures

Cornell Affiliated Author(s)
Author
Isaiah Gray
Takahiro Moriyama
Nikhil Sivadas
Gregory Stiehl
John Heron
Ryan Need
Brian Kirby
David Low
Katja Nowack
Darrell Schlom
Daniel Ralph
Teruo Ono
Gregory Fuchs
Abstract

As electrical control of Neél order opens the door to reliable antiferromagnetic spintronic devices, understanding the microscopic mechanisms of antiferromagnetic switching is crucial. Spatially resolved studies are necessary to distinguish multiple nonuniform switching mechanisms; however, progress has been hindered by the lack of tabletop techniques to image the Neél order. We demonstrate spin Seebeck microscopy as a sensitive tabletop method for imaging antiferromagnetism in thin films and apply this technique to study spin-torque switching in Pt/NiO and Pt/NiO/Pt heterostructures.

Journal
American Physical Society (APS)
Date Published
Funding Source
1719875
Group (Lab)
Katja Nowack Group

Erratum: Spin Hall torques generated by rare-earth thin films [Phys. Rev. B <b>95</b> , 064412 (2017)]

Cornell Affiliated Author(s)
Author
Neal Reynolds
Priyamvada Jadaun
John Heron
Colin Jermain
Jonathan Gibbons
Robyn Collette
Robert Buhrman
D. Schlom
D. Ralph
Abstract

Equation (4) in the original paper contains an incorrect factor of α in the second term of the numerator. The correct equation should be as follows: (Formula Presented). This is a purely typographical error and does not affect any other part of the paper or the analysis. We thank Professor A. Manchon for bringing this error to our attention. © 2019 American Physical Society.

Journal
American Physical Society (APS)
Date Published

Probing and controlling magnetic states in 2D layered magnetic materials

Cornell Affiliated Author(s)
Author
Kin Mak
Jie Shan
Daniel Ralph
Abstract

The discovery of atomic monolayer magnetic materials has triggered significant interest in the magnetism/spintronics and 2D van der Waals materials communities. Here we review recent progress in this rapidly growing field. We survey the physical properties of the large class of layered magnetic materials, and discuss recent advances in the study of these materials in the 2D limit.

Journal
Springer Science and Business Media LLC
Date Published
Funding Source
DMR-1719875
1719875
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

Anisotropic spin-orbit torque generation in epitaxial SrIrO3 by symmetry design

Cornell Affiliated Author(s)
Author
T. Nan
T. Anderson
J. Gibbons
K. Hwang
N. Campbell
H. Zhou
Y. Dong
G . Y. Kim
D. Shao
T. Paudel
N. Reynolds
X. Wang
N. Sun
E . Y. Tsymbal
S . Y. Choi
M. Rzchowski
Yong Kim
D. Ralph
C. Eom
Abstract

Spin-orbit coupling (SOC), the interaction between the electron spin and the orbital angular momentum, can unlock rich phenomena at interfaces, in particular interconverting spin and charge currents. Conventional heavy metals have been extensively explored due to their strong SOC of conduction electrons. However, spin-orbit effects in classes of materials such as epitaxial 5d-electron transition-metal complex oxides, which also host strong SOC, remain largely unreported.

Journal
Proceedings of the National Academy of Sciences
Date Published
Funding Source
DE-FG02-06ER46327
1160504
1708499
1719875
DMR-1629270
FA9550-15-1-0334
W911NF-17-1-0462
DE-AC02-06CH11357
DMR-1708499
DMR-1719875