Ferromagnetic exchange-spring nanocomposites of A1 + L1/sub 0/ CoPt

Abstract

Natural ferromagnetic exchange-spring nanocomposite thin films have been synthesized from sputter-deposited CoPt. Depending upon the details of the annealing treatment, the films consist of two phases in varying proportions: the chemically disordered A1 phase with low coercivity and the chemically ordered L1/sub 0/ phase with high coercivity. Transmission electron microscopy studies reveal fiber texture formation accompanying grain growth in the annealed films and further show that each grain is comprised, on average, of six chemically ordered domains. Magnetic studies show single-phase magnetic character, signaling robust interphase exchange coupling, and indicate that the coercivity development becomes more pinning controlled as the volume fraction of high-coercivity L1/sub 0/ phase increases. The increase of domain wall pinning with increased L1/sub 0/ content is attributed to the microstructure of the L1/sub 0/-ordered phase, which contains nanoscale defects such as antiphase, c-axis variant, and grain boundaries that are a source of effective pinning sites for the narrow (/spl sim/5 nm) domain walls found in L1/sub 0/ CoPt.