Magnetic properties and domain patterns of CoCrPtTa perpendicular films with Ta content

Abstract

The effects of Ta addition or the magnetic properties and domain types in CoCrPtTa were investigated from magnetic force microscopy images and M–H hysteresis loop shapes. A third element is added to the CoCr binary system because high coercivity cannot be obtained from the CoCr binary system. The addition of Pt increases coercivity because of the contribution of the magnetocrystalline anisotropy effect. However, CoCrPt also shows increased media noise due to larger magnetic couplings between columnar grains. For the purpose of avoiding this drawback, magnetic isolation between columnar grains should be attempted, and Cr segregation contributes to this attempt. In addition to magnetic isolation, Ta addition to CoCr is known to enhance Cr segregation. The magnetic isolation between columnar grains of the Co alloy is affected by the segregation of non-magnetic solute atoms. Addition of Ta to CoCrPt shows that the magnetic domain changes from a continuous to a dot-like pattern with increases of Ta content. This indicates that Ta addition weakens the inner segregation of other non-magnetic solute atoms such as Pt or Cr, while it strengthens grain boundary segregation, which leads to the benefit of noise reduction in the high density recording media.