Defined perpendicular anisotropy gradients in the Co sublayers of a [Co(0.6 nm)/Au(2 nm)](3) sputter-deposited multilayer have been introduced by light ion bombardment through a wedged Au stopper layer. Within such a layer system, domain walls between up- and down-magnetized areas are controllably movable by an external perpendicular homogeneous magnetic field. This method and layer system is very promising for a controlled magnetic particle transport within the stray fields of the moving domain walls.
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.
Ga+ or He+ irradiated MBE grown ultrathin films of sapphire/Pt/Co(dCo)/Pt(dPt) were studied using polar Kerr effect in wide ranges of both cobalt dCo and platinum dPt thicknesses as well as ion fluences F. Two branches of increased magnetic anisotropy and enhanced Kerr rotation angle induced by Ga+ or He+ irradiation are clearly visible in two-dimensional (dCo, LogF) diagrams. Only Ga+ irradiation induces two branches of out-of-plane magnetization state.
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