Si segregation in polycrystalline Co2MnSi films with grain-size control

In order to characterize the interface/surface properties of polycrystalline Co2MnSi Heusler alloy films, grain-size evolution with increasing annealing time has been investigated. Here, samples with nanometer-scale grains have been prepared by our specially-designed sputtering system in order to maximize the interface/surface area. Our well-controlled grains clearly show Si phase segregation. This Si phase becomes conductive near room temperature and may be responsible for the significant decrease in tunneling magnetoresistance previously reported by [Wang et al., Appl. Phys. Lett. 93, 122506 (2008)].