Glassy dynamics in an exchange bias nanogranular system: Fe/FeOx

The exchange bias properties of a nanogranular system composed of Fe nanoparticles dispersed in an iron oxide matrix are investigated at different temperatures, in the 5–250 K range, upon varying the cooling field and the temperature at which it is applied. The exchange field, resulting from the exchange coupling between the metallic particles and the oxide matrix, strongly depends on the magneto-thermal history of the sample. Such dependence is consequence of the glassy magnetic nature of the oxide phase and it is explained considering that different frozen spin configurations of the matrix are selected on varying the temperature and the field-cooling process.