Concentric 360 degrees domain wall nesting in magnetic tunnel junction films: a Lorentz TEM study


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O'Shea K. J. , Rode K., Kurt H., McGrouther D., MacLaren D. A.

JOURNAL OF PHYSICS D-APPLIED PHYSICS, vol.48, no.5, 2015 (Journal Indexed in SCI) identifier

  • Publication Type: Article / Article
  • Volume: 48 Issue: 5
  • Publication Date: 2015
  • Doi Number: 10.1088/0022-3727/48/5/055001
  • Title of Journal : JOURNAL OF PHYSICS D-APPLIED PHYSICS

Abstract

We describe the formation of an unusual concentric magnetic domain wall pattern in the free layer of a bottom pinned magnetic tunnel junction. Lorentz microscopy reveals that repeated switching of the free layer with a magnetic field applied perpendicular to the exchange bias direction can produce a series of concentric 360 degrees domain wall loops, a phenomenon we refer to as domain wall nesting. We propose two necessary ingredients for the behaviour: (i) inhomogeneities in the grain-by-grain magnetic dispersion that break local symmetry to produce a preferential sense of magnetic rotation upon field switching; and (ii) structural defects that act to pin 360 degrees domain walls. Further control of this behaviour may provide new functionality for future device applications.