We have used ion irradiation to tune switching field and switching field distribution (SFD) in polycrystalline Co/Pd multilayer-based bit pattern media. Light He+ ion irradiation strongly decreases perpendicular magnetic anisotropy amplitude due to Co/Pd interface intermixing, while the granular structure, i.e., the crystalline anisotropy, remains unchanged. In dot arrays, the anisotropy reduction leads to a decrease in coercivity (HC) but also to a strong broadening of the normalized SFD/HC (in percentage), since the relative impact of misaligned grains is enhanced. Our experiment thus confirms the major role of misorientated grains in SFD of nanodevice arrays.

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