Large and local magnetoresistance in a state-of-the-art perpendicular magnetic medium*

Magnetotransport properties of granular oxide-segregated CoPtCr films were studied on both macroscopic and microscopic length scales by performing bulk and point-contact magnetoresistance measurements, respectively. Such a perpendicular magnetic medium is used in state-of-the-art hard disc drives and, when combined with magnetoresistive phenomena for read/write operations, may lead to a novel concept for magnetic recording with high areal density. The standard bulk measurements of the films showed magnetoresistance of <0.02%. In contrast, the local point-contact measurements revealed giant-magnetoresistance-like changes ΔR in local resistance of the contact R with up to ΔR/R=50,000% ratios. The observed large and local magnetorestive effect is tentatively attributed to a tunnel magnetoresistance between oxide-segregated CoPtCr grains with different coercivity. The tunneling picture of electronic transport in our granular medium was confirmed by the tunneling-like current-voltage characteristics of the contacts and bias dependence of the contact magnetoresistance – both the local point-contact resistance and magnetoresistance were found to decrease with the applied dc bias.