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Magnetic Memory Elements and Sensors

IP.com Disclosure Number: IPCOM000125634D
Original Publication Date: 2000-May-01
Included in the Prior Art Database: 2005-Jun-09
Document File: 3 page(s) / 152K

Publishing Venue

National Institute of Standards and Technology

Related People

Brenda Everitt: INVENTOR [+5]

Abstract

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 dependence of coercivity on element size in submicron magnetic elements. Micromagnetic simulations of a shaped permalloy element show coercivity less than one tenth the coercivity calculated for a rectangular permalloy element of the same size. The switching times for the domain wall traps are shown to be comparable to those of rectangular elements.

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JOURNAL OF APPLIED PHYSICS VOLUME 87, NUMBER 9 1 MAY 2000

Magnetic Memory Elements and Sensors Brenda Everitt, Chairman

Domain wall traps for low-field switching of submicron elements

R. D. McMichaela)

National Institute of Standards and Technology, Gaithersburg, Maryland 20899
J. Eicke Institute for Magnetics Research, The George Washington University, Washington, DC 20052
M. J. Donahue and D. G. Porter National Institute of Standards and Technology, Gaithersburg, Maryland 20899 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 dependence of coercivity on element size in submicron magnetic elements. Micromagnetic simulations of a shaped permalloy element show coercivity less than one tenth the coercivity calculated for a rectangular permalloy element of the same size. The switching times for the domain wall traps are shown to be comparable to those of rectangular elements. @S0021-8979~00!94808-4#

I. INTRODUCTION

  A low switching field and reproducible switching behav- ior are desirable properties of magnetic random access memory cells. The low switching field reduces the power consumed and dissipated by the cell, and the reproducible switching behavior simplifies writing and read back of infor- mation stored in the cell.

  In rectangular cells it has been found that magnetization reversal occurs by expansion of domains that form at the ends of the cell. Because of the symmetry of the rectangle, the end domains can be in a number of different magnetiza- tion states in zero field. Therefore, the switching field may be history dependent.1 The miniaturization of rectangular cells also faces the problem that the coercivity of rectangular cells is inversely proportional to width.2,3

  To overcome the problem of irreproducible switching in rectangular cells, cells with tapered ends have been proposed that nucleate reversals in the middle rather than at the ends of the cells. Although the tapered cells are found to allow more reliable switching than the rectangular cells, it is found that the tapered cells have a higher coercivity than the rectangular cells.4

  Because reversal in both rectangular and tapered-end strips often involves propagation of domain walls, the equi- librium properties of head-to-head walls in thin magnetic strips may provide insight into the switching behavior of rectangles and other shapes. Micromagnetic calculations of head-to-head walls show that the energy of transverse and vortex head-to-head domain walls both increase with in- creasing strip width.5

  In this article, the width dependence of the energy of transverse head-to-head domain walls is used to construct a

domain wall trap. The following describes the important de- sign features and computed switching fields and switching times for domain wall traps, including com...