Anomalous Magnetic Properties of a 2-dimensional Rhomboid Spin Anti-dot Lattice

We fabricated a 2-dimensional spin lattice of circular anti-dots on a silicon substrate by using the photolithography and the wet-etching techniques. A rhomboid lattice symmetry of anti-dots with a diameter of about 1 μm was formed in a 40-nm-thick Co layer with a 5-nm-thick Ni underlayer. The magnetic anisotropy was investigated by using magneto-optical Kerr-effect magnetometry to identify the easy and the hard axes. A systematic study of the magnetic-reversal process was performed using magnetization and magneto-transport measurements with the field applied along the hard axis of the lattice. Anomalous features, a 3-step transition of the magnetization, a nonmonotonous temperature dependence of the coercive field, and a complex behavior of the magneto-resistance data, were observed in the magnetic-reversal process. We speculate that these anomalies originate from the vortex-related phenomena that are inherent in the submicrostructures.