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Search Publications by: Michael J. Donahue (Fed)

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Displaying 1 - 25 of 49

A Novel Low Loss and Lightweight Magnetic Material for Electrical Machinery

February 10, 2020
Michael J. Donahue, Farzad Ahmadi, Yilmaz Sozer, Igor Tsukerman
A new low loss and light weight core material, with applications in electrical machinery, is made of highly packed and insulated magnetic microwires (MWs). These MWs are aligned in such a way as to guide the flux in rotor/stator, with the ultimate goal of

Micromagnetic Study of Soft Magnetic Nanowires

December 27, 2019
Farzad Ahmadi, Michael J. Donahue, Yilmaz Sozer, Igor Tsukerman
In this paper, micromagnetic analysis of an array of long magnetic nanowires (NWs) embedded in a nonmagnetic matrix is performed. It is found that for NWs with diameters on the order of a hundred nanometers, the anisotropy and exchange energies are

Stiff modes in spinvalve simulations with OOMMF

April 1, 2016
Spyridon Mitropoulos, Vassilis Tsiantos, Kyriakos Ovaliadis, Dimitris Kechrakos, Michael J. Donahue
Micromagnetic simulations are an important tool for the investigation of magnetic materials. Micromagnetic software uses various techniques to solve differential equations, partial or ordinary, involved in the dynamic simulations. Euler, Runge-Kutta, Adams

Locally controlled magnetic anisotropy in transcritical permalloy thin films using ferroelectric BaTiO3 domains

November 26, 2014
Michael J. Donahue, Sean W. Fackler, Tieren Gao, Paris N. Nero, Sang-Wook Cheong, John Cumings, Ichiro Takeuchi
We investigated the local coupling between dense magnetic stripe domains in transcritical permalloy (tPy) thin films and ferroelectric domains of BaTiO 3 single crystals in a tPy/BaTiO 3 heterostructure. Two distinct changes in the magnetic stripe domains

Micromagnetic investigation of periodic cross-tie/vortex wall geometry

May 18, 2012
Michael J. Donahue
A systematic series of micromagnetic simulations on periodic cross-tie/vortex wall structures in an ideal soft film at various width, thickness, and period lengths is performed. For each width and thickness a natural period length is found which has

Effects of disorder and internal dynamics on vortex wall propagation

May 26, 2010
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

Direct Imaging of Current Driven Domain Walls in Ferromagnetic Nanostripes

May 21, 2009
Willard C. Uhlig, Michael J. Donahue, Daniel T. Pierce, John Unguris
To better understand the response of domain walls to current induced spin transfer torques, we have directly imaged the internal magnetic structure of domain walls in current-carrying ferromagnetic nanostripes. Domain wall images were acquired both while a

Reversal mechanisms in perpendicular magnetic nanostructures

July 16, 2008
Justin M. Shaw, Stephen E. Russek, Michael J. Donahue, Thomas Thomson, Bruce Terris, Michael Schneider, Miles Olsen
We find that the reversal mechanism in magnetic nanostructures is highly dependent on the nature and condition of the edges. Temperature and size dependent reversal properties of fabricated perpendicularly magnetized nanostructures down to 25 nm in

Numerical Micromagnetics: Finite Difference Methods

September 1, 2007
J. Miltat, Michael J. Donahue
Micromagnetics is based on the one hand on a continuum approximation of exchange interactions, including boundary conditions, on the other hand on Maxwell equations in the non-propagative (static) limit for the evaluation of the demagnetizing field. The

Adiabatic Domain Wall Motion and Landau-Lifshitz Damping

January 1, 2007
Mark D. Stiles, Wayne M. Saslow, Michael J. Donahue, A Zangwill
Recent theory and measurements of the velocity of current-driven domain walls in magnetic nanowires have re-opened the unresolved question of whether Landau-Lifshitz damping or Gilbert damping provides the more natural description of dissipative

Manipulation of magnetic particles by patterned arrays of magnetic spin-valve traps

December 20, 2006
Elizabeth Mirowksi, John M. Moreland, Stephen E. Russek, Michael J. Donahue
A novel magnetic for microfluidic manipulation of magnetic particles is discussed. The particles are confined by an array of magnetic spin valves with bistable ferromagnetic "ON" and antiferromagnetic "OFF" net magnetization states. The switchable fringing

Dynamic Susceptibility of Nanopillars

October 1, 2005
N Dao, I Dumitru, L Spinu, S L. Whittenburg, Michael J. Donahue, J C. Lodder
We have calculated dynamic susceptibility of patterned cobalt and Permalloy pillars with a diameter of 50 nm and different pillar heights using micromagnetic simulations. The resonance modes obtained from these simulations are compared to the results