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Search Publications by: Mark D. Stiles (Fed)

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Displaying 76 - 100 of 200

Mechanism for puddle formation in graphene

December 5, 2011
Author(s)
Shaffique Adam, Suyong S. Jung, Nikolai N. Klimov, Nikolai B. Zhitenev, Joseph A. Stroscio, Mark D. Stiles
Close to charge neutrality, graphene's energy landscape is highly inhomogeneous, forming a sea of electron-like and hole-like puddles that determine the properties of graphene at low carrier density. However, the details of puddle formation have remained

Control of magnetic fluctuations by spin current

September 2, 2011
Author(s)
Vladislav E. Demidov, Sergei Urazhdin, Eric Edwards, Mark D. Stiles, Robert McMichael, Sergej O. Demokritov
We utilize micro-focus Brillouin light scattering spectroscopy to study the interaction of spin current generated by the spin Hall effect with magnetic fluctuations in a Permalloy microdisc. We show that the fluctuations can be efficiently enhanced or

Semiclassical Boltzmann transport theory for graphene multilayers

May 11, 2011
Author(s)
Hongki Min, Parakh Jain, Shaffique Adam, Mark D. Stiles
We calculate the conductivity of arbitrarily stacked multilayer graphene sheets within a relaxation time approximation by considering both short-range and long-range impurities. We investigate theoretically the feasibility of identifying the stacking order

Landau Levels and Band Bending in Few-Layer Epitaxial Graphene

April 18, 2011
Author(s)
Hongki Min, Shaffique Adam, Young J. Song, Joseph A. Stroscio, Mark D. Stiles, Allan H. MacDonald
The carrier density distributions in few-layer-graphene systems grown on the carbon face of silicon carbide can be radically altered by the presence of a Scanning Tunneling Microscope (STM) tip used to probe top-layer electronic properties, and by a

Effects of disorder on magnetic vortex gyration

February 15, 2011
Author(s)
Hongki Min, Robert McMichael, Jacques Miltat, Mark D. Stiles
A vortex gyrating in a magnetic disc has two regimes of motion in the presence of disorder. At large amplitudes the vortex core moves quasi-freely through the disorder potential. As the amplitude decreases, the core can become pinned at a particular point

Current induced torques in the presence of spin-orbit coupling

September 17, 2010
Author(s)
Paul M. Haney, Mark D. Stiles
In systems with strong spin-orbit coupling, the relationship between spin-transfer torque and the divergence of the spin current is generalized to a relation between spin transfer torques, total angular momentum current, and mechanical torques. In

High Resolution Tunnelling Spectroscopy of a Graphene Quartet

September 9, 2010
Author(s)
Alexander F. Otte, Young Kuk, Yike Hu, David Torrance, Phillip First, Walt A. de Heer, Hongki Min, Shaffique Adam, Mark D. Stiles, Allan H. MacDonald, Joseph A. Stroscio
Electrons in a single sheet of graphene behave quite differently from those in traditional two-dimensional electron systems. Like massless relativistic particles, they have linear dispersion and chiral eigenstates. Furthermore, two sets of electrons

Temperature dependence of the diffusive conductivity of bilayer graphene

August 24, 2010
Author(s)
Shaffique Adam, Mark D. Stiles
Assuming diffusive carrier transport and employing an effective medium theory, we calculate the temperature dependence of bilayer graphene conductivity due to Fermi-surface broadening as a function of carrier density. We find that the temperature

Effects of disorder and internal dynamics on vortex wall propagation

May 26, 2010
Author(s)
Hongki Min, Robert D. McMichael, Michael J. Donahue, Jacques Miltat, Mark D. Stiles
Experimental measurements of domain wall propagation are typically interpreted by comparison to ideal models that ignore the effects of extrinsic disorder and the internal dynamics of domain wall structures. Using micromagnetic simulations we study vortex

Anisotropic damping of the magnetization dynamics in Fe, Ni and Co

May 17, 2010
Author(s)
Daniel Steiauf, Jonas Seib, Manfred Faehnle, Keith Gilmore, Mark D. Stiles
The Gilbert parameter alpha describing the damping of magnetization dynamics is commonly taken to be an isotropic scalar. We argue that it is a tensor, that is anisotropic, leading to a dependence of the damping on both the instantaneous direction of the

Magnetic dynamics with spin transfer torques near the Curie temperature.

September 24, 2009
Author(s)
Paul M. Haney, Mark D. Stiles
In this paper we explore the combined action of large thermal fluctuations and spin transfer torques on the behavior of magnetic layers in spin valves. We find that at temperatures near Tc, spin currents can measurably change the size of the magnetization

Spin Transfer Torques by Point-Contact Spin injection

August 24, 2009
Author(s)
Tingyong Chen, Yi Ji, S X. Huang, C L. Chien, Mark D. Stiles
Spin-transfer torques (STT) provide a new mechanism to alter the magnetic configuration in magnetic heterostructures, a feat previously only achieved by an external magnetic field. A current flowing perpendicular through a noncollinear magnetic spin

Evaluating the locality of intrinsic precession damping in transition metals

April 24, 2009
Author(s)
Keith Gilmore, Mark D. Stiles
The Landau-Lifshitz-Gilbert damping parameter is typically assumed to be a local quantity, independent of the magnetic configuration. To test the validity of this assumption we calculate the precession damping rate of small amplitude non-uniform mode

Non-Adiabatic Spin Transfer Torque in Real Materials

March 16, 2009
Author(s)
Ion Garate, Keith Gilmore, Mark D. Stiles, Allan H. MacDonald
The motion of simple domain walls and of more complex magnetic textures in the presence of a transport current is described by the Landau-Lifshitz-Slonczewski (LLS) equations. Predictions of the LLS equations depend sensitively on the ratio between the

A new connection between electricity and magnetism

February 9, 2009
Author(s)
Robert D. McMichael, Mark D. Stiles
A Viewpoint on ``Universal Electromotive Force Induced by Domain Wall Motion,'' Shengyuan A. Yang, Geoffrey S. D. Beach, Carl Knutson, Di Xiao, Qian Niu, Maxim Tsoi and James L. Erskine.

A New Spin on the Doppler Effect

October 17, 2008
Author(s)
Mark D. Stiles, Robert D. McMichael
The coupling between ferromagnetism and electrical current has recently been the object of intense study because of the combination of interesting scientific developments and the potential technological impact. This coupling is mediated by spin current

Ab Initio Studies of the Spin-Transfer Torque in Tunnel Junctions

May 9, 2008
Author(s)
Christian Heiliger, Mark D. Stiles
We calculate the spin-transfer torque in Fe/MgO/Fe tunnel junctions and analyze the results in comparison to all-metallic junctions. We show that the spin-transfer torque is interfacial in the ferromagnetic layer to a greater degree than in spin-valve

Spin Transfer Torques

April 1, 2008
Author(s)
Daniel C. Ralph, Mark D. Stiles
This tutorial article is designed for beginning graduate students who are interested in the physics of spin transfer torques in magnetic devices. We provide an elementary discussion of the mechanism of spin transfer torque, and review the theoretical and

'Ballistic' vs. 'Diffusive' Transport in Current-Induced Magnetization Switching

December 21, 2007
Author(s)
N Theodoropoulou, Abhishek Sharma, W Pratt, J. Bass, Mark D. Stiles, J Xiao
We test whether current-induced magnetization switching due to spin-transfer-torque in ferromagnetic/non-magnetic/ferromagnetic (F/N/F) trilayers changes significantly when scattering within the N-metal layers is changed from ballistic to diffusive. Here

Imaging the interface of epitaxial graphene with silicon carbide via scanning tunneling microscopy

December 14, 2007
Author(s)
Gregory M. Rutter, N Guisinger, Jason Crain, Emily Jarvis, Mark D. Stiles, T Li, P First, Joseph A. Stroscio
The potential for electronics based on graphene, a single layer of sp2-bonded carbon atoms, rests on the ability to fabricate graphene into useful devices. Graphene grown epitaxially on SiC substrates offers an avenue for carbon-based electronics allowing

A Numerical Method to Solve the Boltzmann Equation for a Spin Valve

October 1, 2007
Author(s)
J Xiao, A Zangwill, Mark D. Stiles
We present a numerical algorithm to solve the Boltzmann equation for the electron distribution function in magnetic multilayer heterostructures with non-collinear magnetizations. The solution is based on a scattering matrix formalism for layers that are