Study of microstructure and magnetization reversal mechanism in granular CoCrPt:SiO2 films of variable thickness

The effect of the thickness and microstructural features on the switching behaviour of granular CoCrPt:SiO2 films with perpendicular magnetic anisotropy was investigated. TEM plane view and cross section analysis indicate that, while the very first layers grow as uniform nanograins in close contact, the growth proceeds by formation of well-defined CoCrPt columnar islands (7 nm average size) separated by the silicon oxide, the distance among the islands remaining roughly constant along the whole thickness. The relation between such non-uniform microstructure and the magnetization reversal mechanism at room temperature was investigated by performing hysteresis loops at variable angle as well as time dependent measurements by using a vector vibrating sample magnetometer. Numerical micromagnetic simulations of the hysteresis loops have been carried out to support the description of the experimental observations. The results showed a coexistence of coherent and incoherent reversal processes, the former being more and more pronounced with increasing the magnetic layer thickness, consistently with the microstructural investigations.