Connection Between Intrinsic Interfacial Frozen Spins and Exchange Bias Effect in Core@Shell Iron@Iron-Oxide Nanoparticles

Exchange bias is a common phenomenon that appears at the interfaces between ferromagnetic and ferrimagnetic materials due to the presence of frozen spins. However, systematic quantification of their intrinsic correlation remains to be a challenge. Herein, the exchange bias induced by frozen spins is assumed as the synergy of an effective static magnetic field and an effective anisotropy, and thus the effect of intrinsic frozen spins at core@shell interfaces of iron@iron-oxide nanoparticles is estimated. It is confirmed that the shift of the hysteresis loop is 2322 Oe and the coercivity increases from 360 to 1590 Oe. Using micromagnetic simulations, such a hysteresis loop is reconstructed by introducing an effective static magnetic field of 7360 Oe and an effective anisotropy of 45 x 10(3) J m(-3). Therefore, a connection between the intrinsic interfacial frozen spins and the exchange bias effect is established from a mesoscale perspective, mediated by the effective magnetic field and effective anisotropy. The results can provide an understanding of exchange bias effect and promote applications of ferromagnetic/ferrimagnetic heterostructures.