Exchange bias effects in Fe nanoparticles embedded in an antiferromagnetic Cr_2O_3 matrix

摘要

Powders consisting of ferromagnetic (FM) Fe nanoparticles, of about 7 nm in size, embedded in an antiferromagnetic (AFM) Cr_2O_3 matrix have been obtained by high-temperature reduction under a hydrogen atmosphere of a mixed Cr-Fe oxide. This FM-AFM system exhibits exchange bias effects, i.e. a loop shift (H_E) and coercivity enhancement (DELTA H_C), when field-cooled through the Ned temperature, TN, of Cr_2O_3. The exchange bias properties were measured as a function of temperature. H_E and DELTA H_C are found to vanish at about T_N(Cr_2O_3), indicating a good quality AFM matrix. Hence, high-temperature reduction of mixed oxides is demonstrated to be a suitable technique to develop new types of FM-AFM exchange-biased nanoparticles, from which novel applications of this phenomenon may be developed.