Magnetization reversal in circularly exchange-biased ferromagnetic disks

M. Tanase, A. K. Petford-Long, O. Heinonen, K. S. Buchanan, J. Sort, and J. Nogués
Phys. Rev. B 79, 014436 – Published 27 January 2009
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Abstract

We investigate the reversal behavior of circularly exchange-biased micron-sized bilayer disks of Permalloy (Py)/IrMn and CoFe/IrMn. A circular exchange bias is induced by imprinting the vortex configuration of the ferromagnetic layer into the IrMn when the disks are cooled in zero external field through the blocking temperature of IrMn. The resulting circular exchange bias has a profound effect on the reversal behavior of the ferromagnetic magnetization. In Py/IrMn disks the reversal takes place via vortex motion only, and the behavior is controlled by the exchange bias; it is reversible over a range of small fields and the vortex maintains a single chirality throughout reversal, determined by the chirality of the exchange bias. In CoFe/IrMn disks the non-negligible magnetocrystalline anisotropy causes a reversal via both vortices and domain walls resulting in a finite coercivity, and the behavior is controlled by microstructure. We verify that circular exchange bias does not give rise to a hysteresis loop shift. It lowers coercivity with respect to the field-cooled case, and in Py/IrMn disks it even causes completely reversible magnetic behavior. In both Py/IrMn and CoFe/IrMn disks, circular exchange bias removes the randomness (i.e., stochastic processes due to thermal activation) inherent in single-layer ferromagnetic disks and causes the magnetic behavior to be reproducible over time.

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  • Received 24 September 2008
  • Corrected 6 February 2009

DOI:https://doi.org/10.1103/PhysRevB.79.014436

©2009 American Physical Society

Corrections

6 February 2009

Erratum

Publisher's Note: Magnetization reversal in circularly exchange-biased ferromagnetic disks [Phys. Rev. B 79, 014436 (2009)]

M. Tanase, A. K. Petford-Long, O. Heinonen, K. S. Buchanan, J. Sort, and J. Nogués
Phys. Rev. B 79, 069901 (2009)

Authors & Affiliations

M. Tanase1, A. K. Petford-Long1, O. Heinonen2, K. S. Buchanan3,*, J. Sort4, and J. Nogués5

  • 1Materials Science Division, Argonne National Laboratory, 9700 S Cass Avenue, Lemont, Illinois 60439, USA
  • 2Recording Heads Operation, Seagate Technology, 7801 Computer Avenue, Bloomington, Minnesota 55435, USA
  • 3Center for Nanoscale Materials, Argonne National Laboratory, 9700 S Cass Avenue, Lemont, Illinois 60439, USA
  • 4Institució Catalana de Recerca i Estudis Avançats (ICREA) and Departament de Física, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain
  • 5Institució Catalana de Recerca i Estudis Avançats (ICREA) and Centre d’Investigació en Nanociència i Nanotecnologia (ICN-CSIC), Campus Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain

  • *Present address: Colorado State University, Fort Collins, CO 80523, USA.

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Issue

Vol. 79, Iss. 1 — 1 January 2009

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