Exchange Coupling Properties of Ferromagnetic/Antiferromagnetic Bulk Nanocomposites

Bulk nanocomposites consisting of Ni as ferromagnetic phase and NiO as antiferromagnetic phase are synthesized by severe plastic deformation using high‐pressure torsion. After the solid‐state processing step, an additional annealing step is conducted. The evolving nanostructures in as‐deformed and annealed conditions are analyzed by electron microscopy and correlated to isothermal and thermomagnetic measurements. Both nanocomposites, as‐deformed and annealed, exhibit an exchange biasing mechanism. The interfacial exchange coupling density is influenced by using different field cooling temperatures. The stability of the exchange bias is further investigated. A decrease of the exchange bias is observed with an increasing number of hysteresis loop cycles at low temperatures. Interestingly, the exchange bias is restored through heating the nanocomposite up to room temperature and cooling it to the original measuring temperature without the application of an external field. The thermal stability is investigated by consecutive hysteresis loop measurements from low to room temperature. Even above room temperature, the nanocomposite exhibits an exchange bias.