Complex magnetic ordering in nanoporous [Co/Pd]5-IrMn multilayers with perpendicular magnetic anisotropy and its impact on magnetization reversal and magnetoresistance

We have systematically investigated the magnetization reversal characteristics and magnetoresistance of the continuous and nanoporous [Co/Pd]5-IrMn multilayered thin films with perpendicular magnetic anisotropy at different temperatures (4-300 K). For their nanostructuring, porosity was induced by means of deposition onto templates of anodized titania with small (~30 nm in diameter) homogeneously distributed pores. The magnetization reversal and magnetoresistance of the porous films were found to be closely related to the division of the ferromagnetic material into the regions with different magnetic properties, in correlation with complex morphology of the porous system. Independent magnetization reversal is detected for these regions, which is accompanied with their strong impact on the magnetic order in capping IrMn layer. The electron-magnon scattering is found to be dominant mechanism of magnetoresistance, determining its almost linear field dependence at high magnetic field and contributing to behavior of magnetoresistance, similar to magnetization reversal, at low magnetic field. Partial rotation of IrMn magnetic moments, consistent with magnetization reversal of ferromagnet, is proposed as an explanation for two-state resistance behavior observed in switching between high-resistive and low-resistive values at magnetization reversal of the porous system studied.