Magnetic domain study of micron-and nano-sized permalloy structures induced by a local current

Abstract

In spin-tronic devices such as magnetic random access memory (MRAM), patterned magnetic elements are widely used as unit cells of bit storage. To manipulate data bits, perpendicular electric currents are passed above and below each unit cell to generate the required magnetic field for magnetization reversal. In our work, we study the domain evolution of 40-nm-thick permalloy rods with lengths between 12 I?m and 200 nm with a length:width aspect ratio of 4:1 using a magnetic force microscope (MFM). A simplified MRAM structure which consists of arrays of magnetic elements patterned on top of Au conductors allows us to pass currents and generate localized magnetic fields. The domain changes are compared with results from micro-magnetic simulations (OOMMF) and vibrating sample magnetometer (VSM) measurements. Depending on the applied field angle, domain structures such as quasi-single domain structure, 3-diamond, 2-diamond and 1-diamond structures are observed.