Magnetic microstructures in Co-Cr sputtered thin films for perpendicular recording

The relation between deposition parameters, microstructural and magnetic properties are influencing the reversal mechanism of sputtered Co-Cr thin films having perpendicular anisotropy. Three Co-Cr films with perpendicular coercivities (Hc⊥) of 11, 90 and 170 kA/m are investigated. Besides the Hc⊥ several other parameters were studied by VSM, SEM, NMR, MFM, AFM, selective etching, such as the Hc⊥/Hk, Cr-segregation, domain structure, column sizes, etc. The anomalous Hall effect (AHE) has been used to record the hysteresis curves of sub-micron Hall crosses. This very sensitive technique in combination with e-beam lithography and ion-beam etching resulted in the recording of AHE hysteresis loops with dimensions of the Hall crosses as small as 0.3 × 0.3 μm2. The AHE-loops of three samples, with less than 60 columns, show different magnetic properties and the total number of steps measured in the hysteresis loop was 5 times the number of columns. The different reversal mechanism observed by the AHE are related to differences in microstructure, coercivity and domain size. The analysis of AHE hysteresis loops we conclude that magnetic units on the limit of superparamagnetism could be present in Co-Cr. The obtained results have been used as input for our model for micromagnetic simulations. Micromagnetic simulations shows that the initial layer and the exchange coupling of the initial layer with the columns has a large effect on the magnetisation reversal processes in the film