Shape and strain-induced magnetization reorientation and magnetic anisotropy in thin film Ti/CoCrPt/Ti lines and rings

Abstract

The contributions to the magnetic anisotropy of thin-film rings and lines of width 50 nm and above made from Ti(5 nm)/Co[subscript 0.66]Cr[subscript 0.22]Pt[subscript 0.12] (10 and 20 nm)/Ti (3 nm) with a perpendicular magnetocrystalline anisotropy are investigated, using magnetic force microscopy to image the ac-demagnetized state. Four regimes of behavior were observed in both lines and rings. Samples with the largest widths (>500 nm) showed an out-of-plane maze domain structure typical of unpatterned films with domain widths of ∼200 nm. As the linewidth decreased, a ”bamboo” domain structure forms in which the domain walls lie approximately perpendicular to the linewidth. Further linewidth decreases result in a reorientation to a net in-plane anisotropy perpendicular to the linewidth, and for the narrowest lines, <200-nm wide, the anisotropy reorients in plane parallel to the line. The evolution of anisotropy is modeled in terms of contributions from magnetocrystalline, shape, and first- and second-order magnetoelastic terms, and good agreement with experiment is obtained, considering both bulk and surface anisotropy contributions.