Exchange bias in CoFe-SiO(2) granular nanostructure

Exchange-biased (EB) granular nanostructures are fabricated by sputtering. The EB granular system consists of Co(90)Fe(10) ferromagnetic (FM) nanograms embedded into the insulating S1O(2) matrix, which is sandwiched between antiferrclniagnetic (AFM) Ir(20)Mn(80) layers. The average size of the CoFe nanograms is about 5 nm separated by SiO(2) and the average distance between CoFe nanograms is 1.6 nm for the volume miction of 11.5% SiO(2). Significant asymmetry in the M-H loop of this EB granular nanpstructure reveals that different magnetization reversal mechanisms are involved in toe increasing- and decreasing-field branches of the hysteresis loops. The values of the anisotropy field, H(k) = 96 Oe, and the exchange field, H(ex) = 60 Oe, for the IrMri/CoFe-SiO(2)/IrMn granular nanostructure are obtained which are two times larger than those of the continuous IrMn/CoFe/IrMn film (H(k) = 50 Oe and H(ex) 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 nanograms by the nonmagnetic; phase. This EB granular nanostructure is valuable for understanding theoretical phenomena in EB nanostructures as well as for practical applications.