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
Article Title: Electric-field control of local
ferromagnetism using a magnetoelectric
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
Journal: NAT MATER, Volume: 7, Issue: 6, Page: 478-482,
Year: JUN 2008
* Univ Calif Berkeley, Dept Mat Sci & Engn, Berkeley,
CA 94720 USA.
* Univ Calif Berkeley, Dept Mat Sci & Engn, Berkeley,
CA 94720 USA.
* Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720
* Univ Calif Berkeley, Lawrence Berkeley Lab, Div Mat Sci,
Berkeley, CA 94720 USA.
(addresses have been truncated)
Why do you think your paper is highly
This paper came about at a pivotal time for the field of multiferroics.
Science magazine had put the field of multiferroics on the
"Breakthrough of the Year: Areas to Watch" list (Science
318:1848-49, 2007) vs. 2008. This designation came at a time when
multiferroics had been experiencing more and more attention in solid-state
physics research and increasing participation in symposia focused on these
materials at international meetings.
What multiferroics and magnetoelectrics were promising were novel, new
functionalities in materials. By far, the most fundamental among them is
the ability to control and manipulate magnetism with electric fields. Such
a control has generally been deemed to be very difficult due to the
intrinsic differences between electric field (a polar property) and
magnetic fields (an axial property).
The question of what will make up the next generation of logic, memory, and
sensing technology remains a heated one—this paper brought strong
evidence to support the ideas and concepts that had been on the rise within
the collective field and also demonstrated the powerful nature of these
materials, which are indeed capable of modifying the ferromagnetic state of
an adjoining layer by the application of an electric field to the
Does it describe a new discovery, methodology, or
synthesis of knowledge?
The paper describes a new spin on old materials and new ways of thinking
about using them. The field of functional oxide materials is old and
multiferroics themselves had been studied in Europe and the former Soviet
Union throughout the second half of the last century.
big push in the field of
This figure describes the
main essence of the
Beginning in the early 2000s, multiferroics experienced a "renaissance," as
new ideas, aided by advances in first principles calculations and synthesis
capabilities, about how to create and engineer new multiferroic materials
and utilize them in device structures, exploded onto the research scene.
This was driven by the simple idea that these materials could have greater
impact on future devices where electric fields could be used to control
This paper represented the first real culmination of these ideas in a room
temperature device—finally bringing together the ideas of an entire
field in order to demonstrate the immense capabilities of oxide
With that said, the work really built upon the ideas of an entire field of
study on oxide materials to demonstrate a simple new idea, a new pathway,
to utilizing these materials in order to achieve electric field control of
ferromagnetism at room temperature.
Would you summarize the significance of your paper
in layman's terms?
The modern world is built upon functional materials—materials that
perform exotic tasks unbeknownst to most people on a daily basis, but are
essential to our daily life. From computers to cell phones and beyond, we
rely on the materials in such devices to give us unlimited information and
place such capabilities in the palm of our hand.
As researchers and engineers push the cutting edge of capabilities,
materials are called upon to do more and more. In the realm of computing,
guided by the ever present words of Moore's Law—an observation made
in 1965 by Gordon Moore, co-founder of Intel, which now states that the
number of transistors on a chip doubles every 18 months—we've
achieved more with less in so many ways.
Recently, the question of what comes next after Si, has begun to press on
the minds of many. This is where the cutting edge research at our national
laboratories and research universities comes into play.
From using nanomaterials to the spin of electrons to do computations, the
future is wide open. What this paper demonstrated, in the simplest form, is
a set of materials that could enable this next generation of functional
materials. By using electric fields to control ferromagnetic order, we
begin a dialogue about the possibilities of today's research impacting
How did you become involved in this research, and
were there any problems along the way?
At the University of California, Berkeley, and Lawrence Berkeley National
Laboratory, we had put together a strong program in multiferroic materials
under the direction of Professor Ramamoorthy Ramesh. The group had been
working on various multiferroic and magnetoelectric materials, including
the material BiFeO3 used in this study, for a few years when the
idea to utilize the half-century-old concept of exchange bias with a
magnetoelectric, multiferroic antiferromagnet instead of a classic
antiferromagnet came up.
We assembled a team to attack the problem and I was among the first to join
in on this work. This was truly a project build out of teamwork—both
in the group at Berkeley with our colleagues at Stanford University, the
Advanced Light Source, and the
Swiss Light Source.
The problem we were attempting to address was very complicated and called
on a wide range of skills. From bringing together dissimilar materials, to
developing new device architectures, to pushing the edges of x-ray
photoemission microscopy, there were many issues throughout the research
To get to the end result required countless long days and night shifts at
the synchrotron, and amazing amounts of materials synthesis and device
processing. Each piece of the puzzle offered its own trials and
tribulations, but in the end we persevered and achieved something we were
very proud of. Throughout the numerous iterations we basically invented
processes, analyses, and synthesis techniques that were completely new to
our research team.
Where do you see your research leading in the
I think it is important to make it clear that this is just the beginning of
this field of study. To really utilize these ideas in a device will require
not just a new materials science, but engineering and device integration
that could require years of development.
At the same time, from a fundamental science standpoint, we still have a
number of open questions. The details of the magnetic coupling across
interfaces in such structures has been the focus of much research in the
past and adding dynamical switching to the system only makes it all that
more important to develop new ideas and probes of these sorts of physics.
Other major questions include whether a device can be designed that will
allow for deterministic 180° control of magnetism or if a single-phase
system that is simultaneously both ferroelectric and ferromagnetic at room
temperature with strong coupling can be developed.
The way we view our paper is that we added yet another brick to a bigger
structure—each brick laid before ours enabled us to get where we are
today, and our insights will hopefully enable that next level to go up in
Do you foresee any social or political implications
for your research?
In a field like multiferroics, it is often hard to imagine how our research
will impact the broader world around us. At this point, it would be
presumptuous to say that our research will have significant social or
political implications in the future.
What we can hope for is that our research leads to new ideas and devices
that extend our capabilities—whether they be in computing, memory, or
sensing applications—and that these discoveries enable our daily life
to be just a little bit better.
Lane W. Martin, Ph.D.
Department of Materials Science and Engineering
University of Illinois, Urbana-Champaign
Urbana, IL, USA