Structural and magnetic properties of physical vapor deposited co based thin films

Abstract

We used thermal heating process, under a pressure of 10−7mbar, to synthesize thin films of cobalt on silicon, glass and cupper substrates. The incident beam strikes the substrates under normal and oblique incidences within a home-made design. The thickness ranges from 18 to 400 nm. To investigate the static magnetic properties, the hysteresis loops are performed by means of Vibrating Sample Magnetometer (VSM) and Alternating Gradient Field Magnetometer (AGFM) tools. The zero-field magnetic structure has been investigated by Magnetic Force Microscopy (MFM), using a Veeco 3100 apparatus. To investigate the dynamic magnetic properties, and particularly the magnetic anisotropy in Co x M 1−x/ Si films, we used Brillouin Light Scattering (BLS) experiments, with a (2×3)-pass tandem Fabry-Perot interferometer, and Ferromagnetic Resonance (FMR) technique. All the films are polycrystalline and exhibit a hexagonal close packed (hcp) structure, with the texture. Many films are under stress. The easy magnetization axis lies in the plane of the film whatever is the substrate nature. In Co evaporated on glass, coercivity evolution versus thickness follows a t−n Neel law, symptomatic of Bloch domain motion. MFM images reveal well-defined stripe patterns, mainly for the thickest films. Good agreement is found between the experimental and the calculated spectra in the BLS measurements (fig. 1). This satisfactory accord was obtained by fitting the magneto-crystalline anisotropy field H a , assumed to be uniaxial (H a = 2K u /M s with K u the uniaxial anisotropy constant). From FMR spectra (derivative of the absorption power vs. applied magnetic field H) for the perpendicular configuration, and specifically from the position of the peak (corresponding to the resonant field value) we computed the uniaxial magnetocrystalline anisotropy constant K u (fig. 2). Values of Ku greater than 7 × 106 erg.cm−3 were found for the Co/Si thin films, evaporated under normal incidence. In the obliquely evaporated Co thin films, anisotropy field H a (and magnetic anisotropy constant K u ) has been improved comparative to Co thin films evaporated at a normal incidence. K u value as high as 13 × 106 erg/cm3 has been measured. All these results and others will be presented and discussed.