Nanotechnology, Science and Applications (Jan 2021)
Large and Local Magnetoresistance in a State-of-the-Art Perpendicular Magnetic Medium
Abstract
Morgan Williamson,1,2 Cheng Wang,3 Pin-Wei Huang,3 Ganping Ju,3 Maxim Tsoi1,2 1Physics Department, University of Texas at Austin, Austin, TX 78712, USA; 2Texas Materials Institute, University of Texas at Austin, Austin, TX 78712, USA; 3Fremont Research Center, Seagate Technology, Fremont, CA 94538, USACorrespondence: Maxim Tsoi Email [email protected]: 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 magnetotransport phenomena for read/write operations, may lead to a novel concept for magnetic recording with high areal density.Materials and Methods: The CoPtCr films were deposited by an epitaxy-like sputtering and contained several perpendicularly magnetized granular-media layers with different coercivities; they are very much like the state-of-the-art perpendicular magnetic medium, which can be found in today’s hard disc drives. Magnetoresistive properties of bulk films were assessed by measuring the film resistance in the standard Van der Pauw geometry, while the local transport was probed by the point-contact technique.Results: The bulk measurements showed only a negligible magnetoresistance of less than 0.02%. In contrast, the local point-contact measurements revealed giant-magnetoresistance-like changes ΔR in local resistance of the contact R with more than 10,000% ratio ΔR/R.Conclusion: The observed large and local magnetoresistive effect could be tentatively attributed to a tunnel magnetoresistance between oxide-segregated CoPtCr grains with different coercivities. The tunneling picture of electronic transport in our granular medium was confirmed by the observation of 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.Keywords: magnetoresistance, granular magnetic medium, tunnel magnetoresistance, hard disc drives
