Van der Waals-Zeeman Colloquium

Tuesday, 14 Nov 2006, 16:00h

Magnetism at the nanoscale

Prof. Dominique Givord
Laboratoire Louis Néel, CNRS, Grenoble

The interactions which define the magnetism of matter extend to typically one nanometer. It results that the properties of magnetic nanosystems differ from those observed at the macroscopic scale. General trends characterizing magnetism at the nanoscale will be presented in the first part of this seminar. In the second part, I will focus on two important specific aspects of magnetic nanosystems. The first one is exchange-bias, in which a ferromagnetic material is coupled to an antiferromagnetic one. I will show that the interfacial magnetic coupling occurring between ferromagnetic nanoparticles and the antiferromagnetic matrix inside which the nanoparticles are embedded, can provide an extra source of anisotropy, leading to magnetization stability of otherwise superparamagnetic particles. This phenomenon opens the perspective of stabilizing magnetic bits of information of much smaller size than it is possible today. A unique specificity of metallic nanoobjects is the possibility to modify their magnetic properties by extracting or introducing electrons under an applied electric field. We have demonstrated this effect for the first time in the case of L10 ordered FePt and FePd. In these intermetallics, the coercive field - a parameter which is intimately connected to the intrinsic magnetic properties of these systems - can be reversibly modified under an electric field. The demonstration that low power-consumption electric field actuation may be used in magnetic nanosystems, instead of the usual electrical-current actuation is of high significance for the possible introduction of spin-electronics in electronic and electro-mechanical systems.