Microstructural origin of in-plane magnetic anisotropy in magnetron in-line sputtered CoPtCr thin-film disks

Abstract

The microstructural origin of magnetic anisotropy in a magnetron in-line sputter-deposited CoPtCr/Cr magnetic thin-film disk was examined by mapping magnetic properties and microstructure. The film coercivity (Hc), remanence-thickness product (Mrδ), and coercivity squareness (S*) were determined as a function of radial (r) and angular (θ) co-ordinates using a transfer curve magnetometer. The observed variations in Hc, Mrδ, and S* across the disk were 85 Oe, 0.15 emu/cm2, and 0.03, respectively. The angular variation in magnetic properties showed a sinusoidal pattern with the maxima corresponding to the regions where the tracks were parallel (θ=270°) to the pallet movement direction. High-resolution scanning transmission electron microscopy showed subtle differences in the Co-alloy grain morphology and crystallographic orientation between θ=270° and θ=360° locations. The grains were equiaxed in general except for a small fraction of grains elongated in the direction of pallet movement. Lattice images clearly showed that about 45% of the Co-alloy grains had in-plane c axes and a preferred alignment of the c axes along the texture groove. A greater preference for the c axes to lie along the texture line was observed for the θ=270° location. A coherency stress-based model is proposed to explain the preferred c-axis alignment. While the crystalline anisotropy appears to be the main factor responsible for the magnetic anisotropy, both crystalline and shape anisotropies contribute to the magnetic anisotropy variations.