We have used the Monte Carlo simulation technique to investigate the effect of a ferrimagnetic disordered shell on the hysteresis behavior of composite magnetic nanoparticles with ferromagnetic core/ferrimagnetic disordered shell morphology. We have examined the cooling field $\left(H_{\text{cool}}\right)$ dependence of the exchange bias $\left(H_{\text{ex}}\right)$, the coercive field $\left(H_c\right)$, and the remanent magnetization $\left(M_r\right)$ and we find that an increase in $H_{\text{cool}}$ results initially in an increase in $H_{\text{ex}}$, $H_c$, and $M_r$, while further increase in $H_{\text{cool}}$ causes a reduction in $H_{\text{ex}}$ and $H_c$, but $M_r$ remains constant. Our simulations show that an increase in the shell thickness for a given core size enhances the exchange bias field and reduces the remanent magnetization, the vertical shift, and the training effect. We also find that a reduction in the core size for a given particle size results in an increase in both exchange bias and coercive field. This behavior is reversed as the temperature increases. Our results are in good agreement with experimental findings.

• Received 11 November 2008

DOI:https://doi.org/10.1103/PhysRevB.79.144402