Abstract
Exchange-biased (EB) granular nanostructures are fabricated by sputtering. The EB granular system consists of Co90Fe10 ferromagnetic (FM) nanograins embedded into the insulating SiO2 matrix, which is sandwiched between antiferromagnetic (AFM) Ir20Mn80 layers. The average size of the CoFe nanograins is about 5 nm separated by SiO2 and the average distance between CoFe nanograins is 1.6 nm for the volume fraction of 11.5% SiO2. Significant asymmetry in the M–H loop of this EB granular nanostructure reveals that different magnetization reversal mechanisms are involved in the increasing- and decreasing-field branches of the hysteresis loops. The values of the anisotropy field, Hk = 96 Oe, and the exchange field, Hex = 60 Oe, for the IrMn/CoFe–SiO2/IrMn granular nanostructure are obtained which are two times larger than those of the continuous IrMn/CoFe/IrMn film (Hk = 50 Oe and Hex = 30 Oe). The enhancement of coercivity by 1.5 times is also found. Such a large enhancement is attributed to the breakup of large FM domains into small ones due to the isolation of FM nanograins by the nonmagnetic phase. This EB granular nanostructure is valuable for understanding theoretical phenomena in EB nanostructures as well as for practical applications.
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