2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007;
Denver, Colorado
Session S2: Symposium on Exchange Bias
2:30 PM–5:30 PM,
Wednesday, March 7, 2007
Colorado Convention Center
Room: Four Seasons 4
Sponsoring
Unit:
GMAG
Chair: Dan Dahlberg, University of Minnesota
Abstract ID: BAPS.2007.MAR.S2.4
Abstract: S2.00004 : Understanding Thermal Activation Processes in Exchange Bias Systems
4:18 PM–4:54 PM
Preview Abstract
Abstract
Author:
Kevin O'Grady
(The University of York)
The phenomenon of exchange bias has been of major scientific
interest and
technological importance since the 1980s following its discovery by
Meiklejohn and Bean in 1956 [1,2]. Following initial seminal work by
Fulcomer and Charap [3] it has recently become clear that a major
contribution to the phenomena of exchange bias derives from the
fact that
the grains in the antiferromagnetic (AF) layer are capable of
thermally
activated reorientation due to the exchange field from the
ferromagnetic (F)
layer. In this work careful measurement protocols will be
presented that
enable the thermal activation process to be analysed in
considerable detail.
More recently Hoffman [4] has described a spin reorientation
process that
occurs after the AF layer is set which leads to a large shift in
the forward
going hysteresis loop on the first reversal of the F layer. This
effect,
coupled to the thermal activation process, gives rise to the
phenomenon of
training whereby the loop progressively shifts from its original set
direction towards the origin. Lastly we have observed a spin
freezing
phenomena at the interface that can be induced by either
temperature or
applied field which results in a systematic variation of the
exchange bias.
We interpret this effect as being due to paramagnetic like spins
at the
interface whose ordering leads to a significant increase in the
overall
value of the exchange bias. Thus we show that exchange bias is a
complex
convolution of at least three distinct effects, all of which will be
described in detail. This explains why single theories of how
this effect
arises have been so unsuccessful during the last 50 years.
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[1] Meiklejohn and Bean: Physical Review vol.102 p.1413 (1956)
\newline
[2] Nogues and Schuller: Journal of Magnetism and Magnetic
Materials vol.192
p.203 (1999)
\newline
[3] Fulcomer and Charap: Journal of Applied Physics vol.43
p.4190 (1972)
\newline
[4] Hoffmann: Physical Review Letters vol.93 p.097203 (2004)
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2007.MAR.S2.4