Tuning coercivity in CoCrPt-SiO2 hard disk material

In order to continuously increase the storage capacity of modern computer disk drives and push the superparamagnetic limit to the smallest achievable bit sizes the material used has to fulfill a number of requirements: i) Maximum perpendicular magnetic anisotropy to guarantee thermal stability. Granular CoCrPt-SiO2 films are currently the material of choice. ii) Large remnant magnetization to achieve a good signal to noise ratio when reading the bit information. iii) Moderate coercive fields to allow for the writing of the bit information with the limited write head fields available. In order to increase the storage density, smaller grains with larger magnetic anisotropies are required for thermal stability which are accompanied by large coercive fields which obstruct the writing process. One route to overcome this problem is to independently reduce the coercive field without altering the magnetic anisotropy and the remnant magnetization by tailoring the intergranular exchange.
Ion irradiation and implantation has recently been demonstrated to be a viable tool to modify magnetic properties of thin magnetic films and multilayers [1, 2]. Here we demonstrate that by means of ion implantation of Co and Ne a continuous reduction of the coercive field can be achieved without significant modification of the remaining magnetic parameters. In addition to the magnetization reversal behavior of the entire film investigated by magneto-optic Kerr effect and SQUID magnetometry also the magnetic domain configuration in the demagnetized state is imaged by magnetic force microscopy. Moreover, these studies are supported by micromagnetic simulations which allow to further extract information about the intergranular exchange coupling which is the source of the modified coercive field.

[1] J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D: Appl. Phys. 37, R179 (2004).
[2] J. Fassbender, J. McCord, J. Magn. Magn. Mater. 320, 579 (2008).