Structure and local magnetic anisotropy of MBE-grown Co films

Co films of 1000- thickness were grown by molecular-beam epitaxy on substrates of mica, oxidized silicon, and glass at temperatures between -33°C and 800deg;C. X-ray diffraction and nuclear magnetic resonance were used to study the structural quality and phase composition as a function of growth temperature and type of substrate. The magnetic anisotropy of the films was measured using vibrating-sample magnetometry. The film quality is observed to improve sharply for growth temperatures above 200°C. Below this temperature the films have a strong polycrystalline character. Above this temperature the films on mica and oxidized silicon show well defined (111)/(00.2) texture and coherence lengths on the order of the film thickness. The structural phase composition depends on both substrate and growth temperature. For growth on mica at about 500°C an almost single phased hcp Co film was obtained. Above this temperature the fcc phase dominates the structure, whereas below this temperature stacking faults dominate. For the films grown on oxidized silicon the structure is dominated by stacking faults and the fcc phase over the whole growth temperature range. The overall magnetic anisotropy of the films strongly depends on the structural phase composition. Its magnitude can be satisfactorily described by a compositional average of the respective bulk anisotropies.