Magnetic ordering in ultrathin cobalt film covered by an overlayer of noble metals

Abstract

The spatial distribution of magnetic properties studied by polar Kerr-effect-based magnetometry are carried out on an ultrathin cobalt wedge covered with a silver wedge whose slopes are perpendicular to each other and subsequently capped with a gold layer. The coercivity field was studied as a function of both cobalt thickness d and silver thickness h. A few monolayers of Ag were found to have a substantial influence on the coercivity field. A similar strong influence of silver coverage on the magnetic anisotropy field was observed. Domain structure evolution during magnetization reversal is investigated using an optical microscope. With an increase of the magnetic field, a magnetization reversal process occurs: first by domain nucleation and next by a domain wall movement towards the higher coercivity region of the sample. Changes of the fractal dimension of the domain wall as well as nucleation center density are investigated. A rapid increase of these parameters is observed while d increases towards the value of spin reorientation transition, which goes from easy-axis to easy-plane magnetization. Similar strong changes were observed while decreasing d to the lowest thickness available for observation. The problem discussed here, of tuning magnetic properties by silver–gold structure, is important from both a general physics and an application point of view, especially because of the possibilities for magnetic film patterning.