Nonuniform and sequential magnetization reversal via domain structure formation for
multilayered system with grain size induced enhanced exchange
bias |
| |
Authors: | Email author" target="_blank">A?PaulEmail author E?Kentzinger U?Rücker D E?Bürgler P?Grünberg |
| |
Institution: | (1) Institut für Festkörperforschung, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany |
| |
Abstract: | We report on the magnetization reversal in series of
exchange-biased multilayers
NiFe(10.0 nm)/ Ir20Mn80(6.0 nm)/Co80Fe20(3.0 nm)] N studied by specular
reflection and off-specular scattering of polarized neutrons. All
specimens are sputtered and post-annealed at 530 K (i.e. above the
IrMn Néel temperature of 520 K) in Ar atmosphere before cooling
to room temperature in the presence of a field of 130 Oe which
induces the unidirectional anisotropy. We find HEB is
dependent upon the number of bilayers N as it gradually
increases from 0.33 kOe for N=1 to a considerably higher value
of upto ≈0.9 kOe for N=10. X-ray specular and diffuse
scattering data reveal no significant variation of the lateral
correlation length and only a weak dependence of the vertical rms
interface roughness on N. Atomic and magnetic force microscopy,
however, show a strong reduction of the grain size accompanied by
distinct changes of the ferromagnetic domain structure. The
enhancement of the exchange bias effect is presumably related to
the shrinking of the related domain size in the antiferromagnet
due to the structural evolution in the multilayers. Polarized
neutron reflectometry (PNR) measurements are done at different
applied fields sweeping both branches of the hysteresis loop. The
spin-flip (SF) cross section of both the N=10 and 3 samples
show diffusely scattered intensity appears gradually as the field
approaches HEB and is most intense where the net
magnetization vanishes. The disappearance of diffuse scattering in
saturation indicates that the off-specular intensity is related to
the reversal process. The reversal proceeds sequentially starting
with the bottom (top) CoFe layer for decreasing (increasing) field
and is related to the evolution of the grain size along the stack.
The reversal of each CoFe layer is for both field branches due to
domain wall motion. Thus as a main result, we observe a
sequential and symmetric magnetization reversal in
exchange-biased multilayers. The concomitant in-plane
magnetization fluctuations revealed by off-specular
spin-flip scattering indicate a more complex reversal mechanism
than hitherto considered. Moreover, although the grain size
decreases from N=3 to 10 by a factor of about four the reversal
mechanism remains similar. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|