Tailoring the FePt orientation on amorphous substrates by magnetron sputtering, structural and magnetic investigations

Towards an increase of the magnetic recording density, materials with a high magnetic anisotropy are strongly recommended to overcome the physical limits due to superparamagnetism. For this reason, FePt alloys are widely studied because of the excellent magnetocrystalline anisotropy (KU ~ 5-8 x 10-7 erg/cm3) and large magnetic moments at 300K. [1] But, for perpendicular recording media, a (001) preferential orientation, perpendicular to the layer surface, is required.
10 and 15 nm Fe55Pt45 layers were deposited by dual magnetron sputtering on amorphous SiO2 / Si (001) substrate, varying the deposition methods, form co-deposition to monolayers sequence deposition, and working gas, from Ar to Xe, at 0.3 Pa.
The Ar plasma is more energetic than the Xe one: it is characterized by sputtered atoms with a mean energy of about 12 eV and Ar reflected neutrals, reaching a mean energy of about 100 eV when backscattered from the Pt target. This energy budget that enhance the surface adatom mobility during deposition (few eV are required), and create vacancies (E > 40 eV), that decrease the phase transition temperature to 450°C for thin layers. [2]
But, the impact of energetic atoms supports a vertical layers intermixing resulting in a randomly oriented FePt A1 structure at RT. Subsequent Rapid Thermal Annealing at 750°C is completely transforming the layer into the L10 phase, with a coercivity field HC = 1 T, but introducing a weak perpendicular magnetic anisotropy, not evidencing any difference between the deposition techniques.
The reduction of the plasma energy, by using Xe as working gas, is not decreasing the layer magnetic properties (HC = 1 T) after annealing, but strongly enhance the (001) preferential orientation, with a dispersion of the (001) direction around the surface normal of 6°, already in the co-deposition experiment.
The layer by layer technique, associated with Xe plasma, supports the (001) layer orientation after RTA at 750°C, underlining the importance to reduce the elements diffusion path to an atomistic scale. [3]

[1] H. Kanazawa, G. Lanhoff, T. Suzuki, J. Appl. Phys. 87 (2000) 6143
[2] V. Cantelli, J. von Borany, A. Mücklich, Shengqiang Zhou, J. Grenzer,
Nucl. Instr. and Meth. B, 257, 1-2 (2007) 406-410.
[3] M. L. Yan, N. Powers, D. J. Sellmyer, J. Appl. Phys. 93, 8292 (2003)