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Polystyrene nanosphere arrays are used as the substrate for [Pt/Co]nCoO multilayer deposition. The effects of nanosphere size and CoO thicknesses on the magnetic properties of [Pt/Co]nCoO multilayer nanocaps are investigated. With decreasing nanosphere diameter, the nanocaps exhibit systematic variations of coercivity, exchange bias field, and switching field distribution. The switching field distribution is broadened and the coercivity is enhanced when the nanosphere sizes decrease, which are ascribed to the magnetic dipole-dipole interaction of the isolated nanocaps when the thickness of multilayer is far below the nanosphere radius. The mixture formation and the anisotropy direction changes of Co and CoO interface play an important role in the variation of the exchange bias field when the multilayer film is deposited on the nanosphere with diameter of 60 nm.

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In this study, we investigated the stochastic nature of domain reversal dynamics in exchange-biased IrMn/CoFe film using a time-resolved Kerr microscope. Interestingly, the statistical distributions of the magnetization half-reversal times for both forward and backward applied fields show that the magnetization reversal dynamics is much more stochastic for the backward branch, where an applied field is parallel to the exchange-bias field direction. The enhanced stochasticity is ascribed to the large degree of magnetic disorder during backward reversal, which induces discrete and random Barkhausen jumps, whereas the forward branch reversal is dominated by a thermally activated depinning process caused by a single potential barrier. This result can be explained by the asymmetry of the magnetic disorder between both branches of a hysteresis loop. V

The [Co/CoO] 5 multilayer nanocap arrays are fabricated on the colloidal sphere arrays which are prepared on the Si substrate by the self-assembly technology. Compared to bilayer film, the H EB of multilayer film is larger than that of the bilayer film. The increase of H EB for multilayer should be ascribed to the interface increase between FM and AFM layers. In the multilayer film structure, H EB of the nanocap array is bigger than that of the flat film, which is attributed to the decrease of FM layer thickness, the decrease of grain size, and the increase of structural defects caused by curved substrate. And the typical step is observed in flat, and the step is reduced significantly in the nanocap array due to the enhancement of interfacial coupling between neighbor FM layers. For the [Co/CoO] 5 multilayer nanocap array, H EB increases first, and then decreases when CoO sublayer thickness changes. When CoO sublayer thickness is 15 nm, H EB reaches its maximum. This result may be related to the topography of nanostructure multilayer on curved substrate.