Josep Nogués Talks About Exchange Bias in Nanostructures
Fast Moving Front Commentary, November 2010
|
Article: Exchange bias in nanostructures
Authors: Nogues, J;Sort, J;Langlais,
V;Skumryev, V;Surinach, S;Munoz, JS;Baro, MD |
Josep Nogués talks with ScienceWatch.com and answers a few questions about this month's Fast Moving Fronts paper in the field of Physics.
Why do you think your paper is highly
cited?
The article has become one of the reference works in the field of exchange coupling between ferromagnetic materials and antiferromagnetic materials (i.e., the so-called "exchange bias"). Although there existed several review articles on exchange bias in thin films before our article, this was the first one to focus in detail towards nanostructures.
The main reasons for its high number of citations probably lie first in its completeness (which has given researchers useful background material) and second in its proper timing. Namely, "exchange bias in nanostructures" has been developing rapidly in the last few years both due to the appealing, unsolved, basic science issues and to its important applications.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
The article is a review, synthesizing the knowledge in the field up to 2005.
Would you summarize the significance of your paper
in layman's terms?
Figure 1:
High resolution transmission electron microscopy image of an exchange
coupled ferrimagnetic-antiferromagnetic, Fe3O4-Fe,
core-shell nanoparticle (figure by G. Salazar-Alvarez).
View larger figure in tab below.
The coupling between two different magnetic materials is one of the components in the device that reads the stored information in the hard disk in our computers (i.e., the read head). As the hard disks have increasing memory capacity the read head has to be made smaller since the each bit of information is smaller. As the device is reduced in size, at some point the properties are no longer the same as in larger devices. This could lead to malfunctions.
Hence, in order to avoid problems in future, more powerful, hard disks, there is a need to understand how the magnetic properties and, in particular, the coupling changes as the size is reduced. Moreover, the coupling between different types of magnetic materials is also interesting since by combining two materials one can obtain a new system with novel or improved properties.
This is especially important for very small materials (in the nanometer range – i.e., 1 million times smaller than 1 mm!) since then the coupling area between the two magnetic materials is very large compared to their volume and controls the overall properties. This type of coupling could, for example, bring about stronger permanent magnets or more sensitive magnetic sensors.
How did you become involved in this research, and
how would you describe the particular challenges, setbacks, and
successes that you've encountered along the way?
I began working in the field of exchange bias in thin films when I started my postdoc at the University of California, San Diego, in 1993. When I moved to Barcelona in 1997 (Universidad Autònoma de Barcelona and later Institut Català de Nanotecnologia), I became more interested on the effects of size reduction (in the submicron and nanometric regimes) would have on exchange bias.
The main challenge has probably been to find simple ways to prepare nanostructured ferromagnetic-antiferromagnetic systems in a controlled manner. Although electron beam lithography is very useful for this purpose down to 100 nm range, to reduce the sizes further is far from trivial.
Nowadays I work mostly in bi-magnetic core/shell nanoparticles where sizes can be controlled down to the nm level. My main success in this field has been to demonstrate that antiferromagnets could be useful to stabilize the magnetism of otherwise superparamagnetic nanoparticles.
Where do you see your research leading in the
future?
Given the current miniaturization trends to allow increasingly higher recording densities there is still a need to understand what the limits are in the exchange bias properties of sub-100 nm ferromagnetic-antiferromagnetic based devices.
Moreover, there is an increasing interest in exchange bias in nanoparticles, both as core-shell structures or in nanoparticles embedded in matrices, since the ferromagnetic-antiferromagnetic coupling gives an extra degree of freedom to control and tailor the properties. Probably, we will see an increased tendency of materials that though exchange couplings can be designed to adapt to specific applications.
Do you foresee any social or political
implications for your research?
Understanding the basic properties of ferromagnetic-antiferromagnetic
exchange coupling will help in developing new types of materials with
improved properties which should lead to, for example, memories that can
store more information, more sensitive sensors or stronger magnets. This
should translate in household products which could help us in our everyday
life. However, I doubt the research could lead to any political
issues.
Josep Nogués
ICREA Research Professor
Centre d'Investigació en Nanociència I Nanotecnologia
(ICN-CSIC)
Campus Universitat Autònoma de Barcelona
Bellaterra (Barcelona)
Spain
Web
KEYWORDS: EXCHANGE BIAS; MAGNETIC NANOSTRUCTURES; ANTIFERROMAGNETIC MATERIALS; MAGNETIC DOMAINS, MAGNETIC TUNNEL-JUNCTIONS; RANDOM-ACCESS MEMORY; SPIN-VALVE HEADS; MONTE-CARLO SIMULATIONS; METAL-EVAPORATED TAPES; GB/IN(2) RECORDING DEMONSTRATION; ULTRAFINE IRON PARTICLES; FERROMAGNETIC-ANTIFERROMAGNETIC COMPOSITES; GIANT MAGNETORESISTANCE PROPERTIES; ARTIFICIALLY STRUCTURED MATERIALS.
