Effect of dual underlayer structure on the perpendicular magnetization of FePt:C nanocomposite films

Abstract

The FePt thin films with both ordered face-centered-tetragonal (fct) structure (known as L1 0) and good perpendicular alignment have been synthesized on economical glass substrates and they are deposited at substrate temperature just heated up to 600 °C by heater in sputter apparatus without subsequent thermal annealing process. A strong (0 0 1) oriented FePt film could be obtained with controlling the thickness of either polycrystalline Pt or MgO layer in dual underlayer structure and intercalating ultrathin amorphous carbon layer of 0.75 nm. The formation of ordered fct structure ( L1 0) was confirmed by X-ray diffraction, and visible FePt (0 0 1) and (0 0 2) peaks indicate a high degree for texturing. The FePt:C film deposited on Pt(20 nm)/MgO(35 nm) dual underlayer shows a large perpendicular magnetization, indicating the high ratio (∼15.2) of perpendicular (>7400 Oe) to in-plane (<490 Oe) coercivity. Transmission electron microscope (TEM) observations show that FePt grains become isolated from neighboring grains in carbon matrix. The FePt grains were relatively uniform with average sizes about 9 nm. The obtained results suggest that these processes might be effective for improving the perpendicular magnetization of FePt thin films.