The effect of field-cooling strength and interfacial coupling on exchange bias in a granular system of ferromagnetic nanoparticles embedded in an antiferromagnetic matrix

Abstract

A modified Monte Carlo Metropolis method is performed to simulate the effect of field-cooling strength and interfacial coupling on exchange bias and coercivity of a system with ferromagnetic cores embedded in an antiferromagnetic matrix, based on three-dimensional classical Heisenberg model. The results show that the exchange bias changes from negative value to positive value with increasing cooling field as the interfacial coupling is antiferromagnetic, whereas coercivity is almost unchanged due to the small size of ferromagnetic cores. After applying a weak cooling field, the exchange bias of system with antiferromagnetic interfacial coupling may be positive just when the value of interfacial coupling is not large and exhibit a positive maximum. However, the exchange bias is constantly positive and increasing with increasing values of interfacial coupling after applying a strong cooling field. The exchange bias of system with ferromagnetic interfacial coupling is independent of cooling field and increases for larger interfacial coupling, but the sign is negative due to the constantly positive net magnetization of antiferromagnetic surface. It is obvious that the positive exchange bias depends on the field-cooling strength to a large extent. However, the interfacial coupling may change the configuration of antiferromagnetic matrix to influence the exchange bias.