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Search Publications by: Michael J. Donahue (Fed)

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Displaying 26 - 49 of 49

Velocity of Transverse Domain Wall Motion Along Thin, Narrow Strips

June 1, 2004
Author(s)
Donald G. Porter, Michael J. Donahue
Micromagnetic simulation of domain wall motion in thin, narrow strips leads to a simplified analytical model. The model accurately predicts the same domain wall velocity as full micromagnetic calculations, including dependence on strip width, thickness

Zigzag Shaped Magnetic Sensors

January 1, 2004
Author(s)
S da, Willard C. Uhlig, A Kos, Joe Aumentado, Michael J. Donahue, John Unguris, David P. Pappas
Magnetism in zigzag shaped thin film elements is investigated using scanning electron microscopy with polarization analysis, magneto-transport measurements, and micromagnetic simulations. We find that the angle of magnetization alternates along the length

Defect Related Switching Field Reduction in Small Magnetic Particle Arrays

May 15, 2003
Author(s)
Michael J. Donahue, G Vertesy, Martha Pardavi-Horvath
An array of 42 m square, 3 m thick garnet particles has been studied. The strong crystalline uniaxial anisotropy of these particles results in the stable remanent state being single domain with magnetization parallel to the film normal. Magnetooptic

High-speed switching and rotational dynamics in small magnetic thin-film devices

January 1, 2003
Author(s)
Stephen E. Russek, Shehzaad F. Kaka, Robert McMichael, Michael J. Donahue
The intent of this chapter is to review high frequency magnetic device measurements and modeling work at NIST which is being conducted to support the development of high-speed read sensors, magnetic random access memory, and magnetoelectronic applications

Analysis of Switching in Uniformly Magnetized Bodies

September 1, 2002
Author(s)
Michael J. Donahue, Donald G. Porter
A full analysis of magnetization reversal of a uniformly magnetized particle by coherent rotation is presented.The magnetization energy of the particle in the presence of an applied field H is modeled as E = ( 0/2)MT DM - 0HTM.This model includes shape

Micromagnetics Simulation of Asymmetric Pseudo-Spin Valve Dots

January 1, 2002
Author(s)
N Dao, C A. Ross, F J. Castano, Michael J. Donahue, S L. Whittenburg
We present our recent simulation results for Ni79Fe21 (5 nm)/Cu (3 nm)/Co (4nm) pseudo-spin valves. These simulations have been conducted on several different aspect ratios of rectangular dots. Distinct switches of the two magnetic layers were observed. At

Generalization of a Two-Dimensional Micromagnetic Model to Nonuniform Thickness

June 1, 2001
Author(s)
Donald G. Porter, Michael J. Donahue
A two-dimensional micromagnetic model is extended to support simulation of films with non-uniform thickness. Zeeman and crystalline anisotropy energies are scaled by the local thickness, and exchange interaction between neighbor elements is scaled by the

Switching Dynamics and Critical Behavior of Standard Problem No. 4

June 1, 2001
Author(s)
Robert McMichael, Michael J. Donahue, Donald G. Porter, J Eicke
We report switching dynamics for uMAG standard problem no. 4, a 500 nm x 125 nm x 3 nm rectangle of material with properties to mimic Permalloy. Siwtching dynamics are calculated for fields applied instantaneously to an initial s-state: Field 1 at 170o and

Mathematics and Measurement

January 1, 2001
Author(s)
Ronald F. Boisvert, Michael J. Donahue, Daniel W. Lozier, Robert D. McMichael, Bert W. Rust
In this paper we describe the role that mathematics plays in measurement science at NIST. We first survey the history behind NIST's current work in this area, starting with the NBS Math Tables project of the 1930s. We then provide examples of more recent

Behavior of MAG Standard Problem No. 2 in the Small Particle Limit

May 1, 2000
Author(s)
Michael J. Donahue, Donald G. Porter, Robert D. McMichael, J Eicke
For a uniformly magnetized rectangular particle with dimensions in the ratio 5 : 1 : 0.1, the coercive and switching fields in the (1,1,1) direction are determined to be H c / M s = 0.057069478 and H s / M s = 0.057142805. Previous micromagnetic

Domain Wall Traps for Low-Field Switching of Submicron Elements

May 1, 2000
Author(s)
Robert D. McMichael, J G. Eicke, Michael J. Donahue, Donald G. Porter
In magnetic random access memory, power consumption depends on the coercivity of the magnetic elements in the memory cells. In this article a new method is described that uses a domain wall trap element shape to reduce both the coercivity and the

OOMMF User's Guide, Version 1.0

September 1, 1999
Author(s)
Michael J. Donahue
This manual describes OOMMF (Object Oriented Micromagnetic Framework), a public domain micromagnetics program developed at NIST. The program is designed to be portable, flexible, and extensible, with a user-friendly graphical interface. The code is written

Measurement and Standards for Computational Science and Engineering

March 1, 1999
Author(s)
Ronald F. Boisvert, J L. Blue, Daniel W. Lozier, William F. Mitchell, Roldan Pozo, Michael J. Donahue, Donald G. Porter
This report describes current work within ITL on the development of measurement and standards technology to improve the practice of computational science and engineering.

A Variational Approach to Exchange Energy Calculations in Micromagnetics

June 1, 1998
Author(s)
Michael J. Donahue
This paper presents a magnetization interpolation method for micromagnetic exchange energy calculations using a variational procedure to relax spins on a supplemental (refined) lattice. The approximations implicit in standard micromagnetic discretization

Micromagnetic Computational Standard Problem (Abstract)

April 1, 1997
Author(s)
Robert D. McMichael, Michael J. Donahue
Proposed solutions to a standard problem in micromagnetics that were collected anonymously from a number of researchers using a variety of computational techniques are presented. This is the first time that a problem in micromagnetics has been attempted by

Magneto-Optical Indicator Film Study of the Magnetization of a Symmetric Spin Valve

September 1, 1996
Author(s)
Valerian I. Nikitenko, V S. Gornakov, L M. Dedukh, Yury P. Kabanov, A F. Khapikov, Lawrence H. Bennett, P J. Chen, Robert D. McMichael, Michael J. Donahue, L Swartzendruber, Alexander J. Shapiro, H J. Brown, William F. Egelhoff Jr.
A magneto-optical indicator film (MOIF) technique is used for direct experimental study of the magnetization reversal process in a symmetric NiO/Co/Cu/NIFe/Cu/Co/NiO spin valve. It is shown for the first time that the reversal of the free center layer

Magneto-Optical Indicator Film (MOIF) Microscopy of Granular and Layer Structures (Abstract)

April 1, 1996
Author(s)
Valerian I. Nikitenko, V S. Gornakov, L M. Dedukh, A F. Khapikov, Lawrence H. Bennett, Robert D. McMichael, L Swartzendruber, Alexander J. Shapiro, Michael J. Donahue, V N. Matveev, V I. Levashov
We report on the possibilities of application of magneto-optical indicator film (MOIF) technique for visualization and direct experimental study in real time of the magnetization processes and nondestructive characterization of the quality of magnetic thin