Skip to main content

Publications

Low-damping sub-10-nm thin films of lutetium iron garnet grown by molecular-beam epitaxy

Cornell Affiliated Author(s)
Author
C. Jermain
H. Paik
Sriharsha Aradhya
Robert Buhrman
D. Schlom
D. Ralph
Abstract

We analyze the structural and magnetic characteristics of (111)-oriented lutetium iron garnet (Lu3Fe5O12) films grown by molecular-beam epitaxy, for films as thin as 2.8 nm. Thickness-dependent measurements of the in- and out-of-plane ferromagnetic resonance allow us to quantify the effects of two-magnon scattering, along with the surface anisotropy and the saturation magnetization.

Journal
AIP Publishing
Date Published
Funding Source
1120296
1406333

Origin of fieldlike spin-orbit torques in heavy metal/ferromagnet/oxide thin film heterostructures

Cornell Affiliated Author(s)
Author
Yongxi Ou
Chi-Feng Pai
Shengjie Shi
D. Ralph
Robert Buhrman
Abstract

We report measurements of the thickness and temperature (T) dependencies of current-induced spin-orbit torques, especially the fieldlike (FL) component, in various heavy metal (HM)/normal metal (NM) spacer/ferromagnet (FM)/oxide (MgO and HfOx/MgO) heterostructures. The FL torque in these samples originates from spin current generated by the spin Hall effect in the HM.

Journal
American Physical Society (APS)
Date Published
Funding Source
ECCS-1542081
DMR-1120296

Nanosecond-Timescale Low Energy Switching of In-Plane Magnetic Tunnel Junctions through Dynamic Oersted-Field-Assisted Spin Hall Effect

Cornell Affiliated Author(s)
Author
Sriharsha Aradhya
G. Rowlands
J. Oh
D. Ralph
Robert Buhrman
Abstract

We investigate fast-pulse switching of in-plane-magnetized magnetic tunnel junctions (MTJs) within 3-terminal devices in which spin-transfer torque is applied to the MTJ by the giant spin Hall effect. We measure reliable switching, with write error rates down to 10-5, using current pulses as short as just 2 ns in duration.

Journal
American Chemical Society (ACS)
Date Published

All-optical vector measurement of spin-orbit-induced torques using both polar and quadratic magneto-optic Kerr effects

Cornell Affiliated Author(s)
Author
Xin Fan
Alex Mellnik
Wenrui Wang
Neal Reynolds
Tao Wang
Halise Celik
Virginia Lorenz
Daniel Ralph
John Xiao
Abstract

We demonstrate that the magneto-optic-Kerr effect with normal light incidence can be used to obtain quantitative optical measurements of both components of spin-orbit-induced torque (both the antidamping and effective-field components) in heavy-metal/ferromagnet bilayers. This is achieved by analyzing the quadratic Kerr effect as well as the polar Kerr effect. The two effects can be distinguished by properly selecting the polarization of the incident light.

Journal
AIP Publishing
Date Published
Funding Source
DMR-1120296
DMR-1505192
DMR-1010768
ECCS-0335765
N66001-11-1-4110

Scanning SQUID susceptometers with sub-micron spatial resolution

Cornell Affiliated Author(s)
Author
John Kirtley
Lisa Paulius
Aaron Rosenberg
Johanna Palmstrom
Connor Holland
Eric Spanton
Daniel Schiessl
Colin Jermain
Jonathan Gibbons
Y.-K.-K. Fung
Martin Huber
Daniel Ralph
Mark Ketchen
Gerald Gibson
Kathryn Moler
Abstract

Superconducting QUantum Interference Device (SQUID) microscopy has excellent magnetic field sensitivity, but suffers from modest spatial resolution when compared with other scanning probes. This spatial resolution is determined by both the size of the field sensitive area and the spacing between this area and the sample surface. In this paper we describe scanning SQUID susceptometers that achieve sub-micron spatial resolution while retaining a white noise floor flux sensitivity of ≈2μΦ0/Hz1/2.

Journal
AIP Publishing
Date Published
Funding Source
0957616
1120296
1406333
DGE-114747
DMR-0957616
DMR-1406333
DMR-1120296
ECCS-1542081

Atomically Thin Ohmic Edge Contacts Between Two-Dimensional Materials

Cornell Affiliated Author(s)
Author
Marcos Guimarães
Hui Gao
Yimo Han
Kibum Kang
Saien Xie
Cheol-Joo Kim
David Muller
Daniel Ralph
Jiwoong Park
Abstract

With the decrease of the dimensions of electronic devices, the role played by electrical contacts is ever increasing, eventually coming to dominate the overall device volume and total resistance. This is especially problematic for monolayers of semiconducting transition-metal dichalcogenides (TMDs), which are promising candidates for atomically thin electronics. Ideal electrical contacts to them would require the use of similarly thin electrode materials while maintaining low contact resistances.

Journal
American Chemical Society (ACS)
Date Published
Funding Source
1406333
FA2386-13-1-4118
680-50-1311

Strong spin Hall effect in the antiferromagnet PtMn

Cornell Affiliated Author(s)
Author
Yongxi Ou
Shengjie Shi
D. Ralph
Robert Buhrman
Abstract

Effectively manipulating magnetism in ferromagnet (FM) thin-film nanostructures with an in-plane current has become feasible since the determination of a "giant" spin Hall effect (SHE) in certain heavy metal/FM systems. Recently, both theoretical and experimental reports indicate that metallic antiferromagnet materials can have both a large anomalous Hall effect and a strong SHE. Here we report a systematic study of the SHE in PtMn with several PtMn/FM systems.

Journal
American Physical Society (APS)
Date Published
Funding Source
DMR-1120296
ECCS-1542081

Enhanced spin Hall torque efficiency in Pt100-xAlx and Pt100−xHfx alloys arising from the intrinsic spin Hall effect

Cornell Affiliated Author(s)
Author
Minh-Hai Nguyen
Mengnan Zhao
D. Ralph
Robert Buhrman
Abstract

We report that the spin Hall torque generated by Pt can be enhanced substantially by alloying with Al or Hf. We observe damping-like spin torque efficiency per unit applied current density as high as ξDLj=0.23±0.02, nearly twice the maximum value reported for pure Pt. To achieve this maximum efficiency, a very thin (0.5 nm) Pt spacer layer is inserted between the alloy and the ferromagnet being manipulated, to avoid a degraded spin transparency at the alloy/ferromagnet interface. © 2016 Author(s).

Journal
AIP Publishing
Date Published
Funding Source
1542081
DMR-1120296

Manipulating magnetic devices with spin-orbit torques

Cornell Affiliated Author(s)
Author
Daniel Ralph
Abstract

Magnetic devices are a leading contender for the implementation of memory and logic technologies that are non-volatile, that can scale to high density and high speed, and that do not wear out. However, widespread application of magnetic memory and logic devices will require the development of efficient mechanisms for reorienting their magnetization using the least possible current and power. Until recently, the most-efficient known mechanism for manipulating magnetization in practical device geometries was spin-transfer torque from a spin-polarized current.

Conference Name
.
Date Published

Current control of magnetic anisotropy via stress in a ferromagnetic metal waveguide

Cornell Affiliated Author(s)
Author
Kyongmo An
Xin Ma
Chi-Feng Pai
Jusang Yang
Kevin Olsson
James Erskine
Daniel Ralph
Robert Buhrman
Xiaoqin Li
Abstract

We demonstrate that in-plane charge current can effectively control the spin precession resonance in an Al2O3/CoFeB/Ta heterostructure. Brillouin light scattering was used to detect the ferromagnetic resonance field under microwave excitation of spin waves at fixed frequencies. The current control of spin precession resonance originates from modification of the in-plane uniaxial magnetic anisotropy field Hk, which changes symmetrically with respect to the current direction.

Journal
American Physical Society (APS)
Date Published
Funding Source
DE-SC0012670
DMR-1120296
DMR-1206404