Grupo de Materiales Magnéticos (GMM). Universidad de Castilla-La Mancha

Research line: Exchange Bias in nanostructured systems

The exchange bias phenomenon appears between a ferromagnetic material (FM) and an antiferromagnetic material (AFM) when field cooling from above the Néel temperature, TN, of the AFM (and below the Curie temperature of the FM), and it appears as a horizontal shift in the hysteresis loop. This magnetic coupling has recently attracted much attention for being a mechanism to stabilize the magnetic moment of FM nanoparticles (NPs) at high temperatures (depending on the TN of the AFM). In particular, Co NPs can be stabilized at temperatures close to room temperature due to the EB with CoO.

Our group has performed several studies of the system Co-CoO obtained by two different methods:

• Frustrated Ag/Co multilayers grown by reactive sputtering. In Ag/Co multilayers, a discontinuous layer of Co is obtained for thickness of the layer below 4 nm, giving place to granular films of Co NPs embedded in an Ag matrix. If we add a little bit of oxygen during the deposition, these Co NPs are partially oxidized, CoO is formed and exchange bias appears.


• Co NPs grown by gas-phase aggregation in a cluster gun system. The gas-phase aggregation allows obtaining Co NPs with a narrow size distribution. If these Co NPs are oxidized in a controlled way, NPs with core-shell structure can be obtained (with a core of Co –FM- and a shell of CoO –AFM-). In our group we have set-up a system allowing us to fabricate NPs with a cluster gun and embed them in different kind of matrixes grown by sputtering (Nb, C, Cu, Si…).