Lane W. Martin talks with
ScienceWatch.com and answers a few questions
about this month's New Hot Paper in the field of
Materials Science. The author has also sent along
images of their work.
Article Title: Electric-field control of local
ferromagnetism using a magnetoelectric
multiferroic
Authors: Chu,
YH;Martin,
LW;Holcomb, MB;Gajek, M;Han, SJ;He, Q;Balke,
N;Yang, CH;Lee, D;Hu, W;Zhan, Q;Yang,
PL;Fraile-Rodriguez, A;Scholl, A;Wang, SX;Ramesh,
R
A big push in the field of
multiferroics has focused on
engineering strong magnetoelectric
coupling. The magnetoelectric effect
describes the coupling between electric
and magnetic fields in matter. Strong
magnetoelectric coupling in materials
would enable a new generation of
devices where we could say manipulate
magnetic data bits with an electric
field. Another idea is to evolve
computational capabilities to utilize
not only the presence of charge, but
the spin of the electrons. The so
called field of spintronics
would need materials that can respond
quickly to small applied fields
(typically we envision materials
working with small electric fields to
keep power consumption, heating, etc.
to a minimum) and have deterministic
control of electron spins (i.e.,
magnetic order). Magnetoelectric
materials – like some
multiferroics – offer exciting
opportunities for making these types of
devices a reality.
Figure 2:
Figure 2: Switching
This figure describes the main essence
of the paper we’ve been
discussing. We were attempting to show
that we could control
ferromagnetism with an electric
field. On the left is a schematic
of a cross-sectional view of the device
we used in this study. Very simply, it
consisted of a ferromagnetic materials
(Co0.9Fe0.1, here
called CoFe) in contact with the
magnetoelectric, multiferroic
BiFeO3. The device structure
allowed us to apply electric fields in
the plane of the film between the blue
electrodes. This enabled deterministic
control of the ferroelectric switching
in the BiFeO3. The
antiferromagnetic order in
BiFeO3, in turn, coupled to
the ferroelectric order and upon a
change in the ferroelectricity a
corresponding change in the
antiferromagnetism is obtained. This
antiferromagnetic order is then coupled
to the ferromagnetic order in CoFe via
an exchange interaction. Demonstrated
on the right is what happens to the
ferromagnet upon application of an
electric field. The magnetic domain
structure is observed to switch
back-and-forth by 90° rotations as
imaged via x-ray magnetic circular
dichroism photoemission electron
microscopy.