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Title: Magnetization Damping in Ultrathin Polycrystalline Co Films: Evidence for Nonlocal Effects

Abstract

The magnetic properties and magnetization dynamics of polycrystalline ultrathin Co layers were investigated using a broadband ferromagnetic resonance technique at room temperature. A variable-thickness (1 nm{center_dot}t{center_dot}10 nm) Co layer is sandwiched between 10-nm-thick Cu layers (10 nm Cu|t Co|10 nm Cu), while materials in contact with the Cu outer interfaces are varied to determine their influence on the magnetization damping. The resonance field and the linewidth were studied for in-plane magnetic fields in field-swept experiments at a fixed frequency, from 4 to 25 GHz. The Co layers have a lower magnetization density than the bulk and an interface contribution to the magnetic anisotropy normal to the film plane. The Gilbert damping , as determined from the frequency dependence of the linewidth, increases with decreasing Co layer thickness for films with outer Pt layers. This enhancement is not observed in structures without Pt layers. The result can be understood in terms of a nonlocal contribution to the damping due to spin pumping from Co through the Cu layer and spin relaxation in Pt layers. Pt layers just 1.5 nm thick are found to be sufficient to enhance the damping and thus act as efficient 'spin sinks'. In structures with Pt outermore » layers, this nonlocal contribution to the damping becomes predominant when the Co layer is thinner than 4 nm.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
930604
Report Number(s):
BNL-80910-2008-JA
Journal ID: ISSN 1098-0121; TRN: US200904%%613
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review B: Condensed Matter and Materials Physics; Journal Volume: 74
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; COBALT; THIN FILMS; POLYCRYSTALS; MAGNETIC PROPERTIES; MAGNETIZATION; SPIN; COPPER; PLATINUM; LAYERS; national synchrotron light source

Citation Formats

Beaujour,J., Lee, J., Kent, A., Krycka, K., and Kao, C. Magnetization Damping in Ultrathin Polycrystalline Co Films: Evidence for Nonlocal Effects. United States: N. p., 2006. Web. doi:10.1103/PhysRevB.74.214405.
Beaujour,J., Lee, J., Kent, A., Krycka, K., & Kao, C. Magnetization Damping in Ultrathin Polycrystalline Co Films: Evidence for Nonlocal Effects. United States. doi:10.1103/PhysRevB.74.214405.
Beaujour,J., Lee, J., Kent, A., Krycka, K., and Kao, C. Sun . "Magnetization Damping in Ultrathin Polycrystalline Co Films: Evidence for Nonlocal Effects". United States. doi:10.1103/PhysRevB.74.214405.
@article{osti_930604,
title = {Magnetization Damping in Ultrathin Polycrystalline Co Films: Evidence for Nonlocal Effects},
author = {Beaujour,J. and Lee, J. and Kent, A. and Krycka, K. and Kao, C.},
abstractNote = {The magnetic properties and magnetization dynamics of polycrystalline ultrathin Co layers were investigated using a broadband ferromagnetic resonance technique at room temperature. A variable-thickness (1 nm{center_dot}t{center_dot}10 nm) Co layer is sandwiched between 10-nm-thick Cu layers (10 nm Cu|t Co|10 nm Cu), while materials in contact with the Cu outer interfaces are varied to determine their influence on the magnetization damping. The resonance field and the linewidth were studied for in-plane magnetic fields in field-swept experiments at a fixed frequency, from 4 to 25 GHz. The Co layers have a lower magnetization density than the bulk and an interface contribution to the magnetic anisotropy normal to the film plane. The Gilbert damping , as determined from the frequency dependence of the linewidth, increases with decreasing Co layer thickness for films with outer Pt layers. This enhancement is not observed in structures without Pt layers. The result can be understood in terms of a nonlocal contribution to the damping due to spin pumping from Co through the Cu layer and spin relaxation in Pt layers. Pt layers just 1.5 nm thick are found to be sufficient to enhance the damping and thus act as efficient 'spin sinks'. In structures with Pt outer layers, this nonlocal contribution to the damping becomes predominant when the Co layer is thinner than 4 nm.},
doi = {10.1103/PhysRevB.74.214405},
journal = {Physical Review B: Condensed Matter and Materials Physics},
number = ,
volume = 74,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • No abstract prepared.
  • Due to the collective nature of the electronic interactions responsible for the appearance of ferromagnetic ordering, a strong influence of reduced dimensionality is to be expected in ultrathin magnetic films and heterostructures. In this article we review a number of experimental results covering several of those effects. For instance, the coercivity of ultrathin Co/Cu(111) films increases continuously up to {similar_to}6 monolayer Co thickness. We show that this behavior is related to the thickness dependence of the Curie temperature of these low-dimensional samples. Moreover, magnetic anisotropy and interlayer exchange coupling are also strongly affected by the structural features. Because of theirmore » smaller interfacial roughness, films grown with the aid of a surfactant Pb layer exhibit perpendicular magnetization up to larger thicknesses than those grown without Pb. With respect to the exchange coupling, the first ones show oscillatory magnetic coupling and complete antiferromagnetic coupling for both perpendicular and parallel magnetization between Co layers, while for films grown without Pb there is always some amount of ferromagnetic coupling between Co layers. {copyright} 2001 American Institute of Physics.« less
  • We observe a systematic increase in interface perpendicular magnetic anisotropy (PMA) with increasing Au-interlayer thickness t{sub Au} ranging from 1 to 5 monolayers (MLs) in Cu/Co/Au/Cu(111), where misfit strain in Co due to the epitaxial growth increases with increasing t{sub Au}. This result can be understood within the framework of the magneto-elastic contribution to the interface PMA. With a Cu overlayer, a constant contribution of interface PMA as well as of volume anisotropy is observed when the Co thicknesses are greater than 1.3 ML. However, we have found an unexpected suppression of this variation of interface PMA with the usemore » of Au overlayers instead of Cu ones. With Au or Pd overlayers, the PMA starts to degrade as the Co thickness is reduced below 2.5 ML. (c) 2000 American Institute of Physics.« less
  • We have observed magnetic-field-dependent enhancements as large as a factor of 20 of the intensity of [ital elastic]-light scattering, from ultrathin magnetic films with perpendicular magnetic anisotropy. High-resolution Brillouin spectroscopy shows that this enhancement reaches its maximum at a critical field (H[sub crit]) where the magnetization starts to incline toward out-of-plane due to the perpendicular anisotropy. We attribute this effect to the microscopic instability due to random fluctuations of the magnetization near H[sub crit]. [copyright] [ital 1999] [ital The American Physical Society]
  • The magnetization of body-centered-cubic iron was measured by means of polarized neutron reflection on a set of films of different thickness (4, 6, 8, and 16 A). The films were epitaxially deposited onto polished (100) MgO substrates and covered by protective layers of gold. The results show that at 40 K all films are ferromagnetic, with an average magnetic moment per iron equal to 2.2[plus minus]0.2[mu][sub [ital B]] regardless of film thickness. However, the thinnest films exhibit a Curie temperature lower than that of the bulk and a magnetization axis tilted out of the film surface. These results are discussedmore » in the light of the detailed morphology of the films, and compared with the theoretical predictions.« less