Vortex dynamics in Co-Fe-B magnetic tunnel junctions in presence of defects. M. Kuepferling, S. Zullino, A. Sola, B. Van de Wiele, G. Durin, M. Pasquale, K. Rott, G. Reiss, a., G., B. Journal of Applied Physics, 117:17E107, 2015.
Vortex dynamics in Co-Fe-B magnetic tunnel junctions in presence of defects [pdf]Paper  abstract   bibtex   
We investigate the frequency of thermally excited vortex oscillations in Co-Fe-B magnetic tunnel junction (MTJ) pillars in the presence of defects. Under a variable in-plane magnetic field, a characteristic behavior is observed: the frequency oscillates from a maximum at certain field values to a steep minimum, which tends towards zero frequency. These frequency variations are described qualitatively well by an analytical model based on the Thiele equation taking into account a single Gaussian pinning potential. It is thus possible to calculate the in-plane depinning field for certain pinning potential parameters. For steep potentials, the depinning is hysteretic and jumps between the pinned and unpinned regime occur due to the presence of an energy barrier. A sharp frequency minimum occurs at an applied field, where a large flat region in the energy landscape is present. From the experiments, the pinning potentials are estimated to be between 0.2eV and 0.4eV. We also perform micromagnetic simulations of the vortex oscillations in the presence of a distribution of pinning centers. The simulations confirm the validity of the Thiele-approach showing that the vortex remains sufficiently rigid.
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 title = {Vortex dynamics in Co-Fe-B magnetic tunnel junctions in presence of defects},
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 year = {2015},
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 pages = {17E107},
 volume = {117},
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 last_modified = {2017-11-06T09:22:37.068Z},
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 citation_key = {M.KuepferlingS.ZullinoA.SolaB.VandeWieleG.DurinM.PasqualeK.RottG.Reiss2015},
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 abstract = {We investigate the frequency of thermally excited vortex oscillations in Co-Fe-B magnetic tunnel
junction (MTJ) pillars in the presence of defects. Under a variable in-plane magnetic field, a characteristic
behavior is observed: the frequency oscillates from a maximum at certain field values to a
steep minimum, which tends towards zero frequency. These frequency variations are described
qualitatively well by an analytical model based on the Thiele equation taking into account a single
Gaussian pinning potential. It is thus possible to calculate the in-plane depinning field for certain
pinning potential parameters. For steep potentials, the depinning is hysteretic and jumps between
the pinned and unpinned regime occur due to the presence of an energy barrier. A sharp frequency
minimum occurs at an applied field, where a large flat region in the energy landscape is present.
From the experiments, the pinning potentials are estimated to be between 0.2eV and 0.4eV. We
also perform micromagnetic simulations of the vortex oscillations in the presence of a distribution
of pinning centers. The simulations confirm the validity of the Thiele-approach showing that the
vortex remains sufficiently rigid.},
 bibtype = {article},
 author = {M. Kuepferling, S. Zullino, A. Sola, B. Van de Wiele, G. Durin, M. Pasquale, K. Rott, G. Reiss, and G. Bertotti},
 journal = {Journal of Applied Physics}
}
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