L10 ordering of magnetron sputtered FePt films at temperatures below 400°C

Due to the high uniaxial anisotropy L10-ordered FePt is currently the most favoured candidate for future high density storage applications. However, in order to achieve the L10-phase either the deposition or post deposition annealing at temperatures above typically 500°C is required. Many attempts ranging from alternating monolayer deposition [1], different seed or cap layers [2] or doping with third elements [3] have been tried to reduce the ordering temperature with various degree of success.
Here we report on the L10-ordering of stoichiometric 30-125 nm thick FePt films which have been magnetron co-sputtered from elemental targets on SiO2/Si substrates with a deposition rate of (0.30-0.2) Å/s at various temperatures. Surprisingly, already for a deposition at 350°C the films are well chemically ordered in the tetragonal L10 structure with a long- range order parameter S=0.8-0.9 which has been determined by grazing incidence X-ray diffraction. The films exhibit a polycrystalline fiber texture with mean grain sizes of 12-18 nm and a random orientation distribution confirmed by pole figures measurements. In contrast, FePt films deposited at room temperature exhibit the fcc A1-phase with a mean grain size of (5.0 - 0.5) nm. In a sequence of annealing steps with successively increased temperatures, the A1 - L10 transition has been obtained between 300-400°C. After annealing at 400°C the films show nearly complete L10 ordering with S values equivalent to the films deposited at 350°C. During annealing the mean grain size grows to 10-12 nm. Using textured seed layers L10 ordered FePt films with preferred orientation can be realized. One of the key issues in observing the L10-ordering already at rather low temperatures is a combination of low deposition rate and low-energy ion irradiation during deposition.

[1] T. Shima, T. Moriguchi, S. Mitani, K. Takanashi, Appl. Phys. Lett. 80, 288 (2002).
[2] Z. L. Zhao, J. Ding, K. Inaba, J. S. Chen, J. P. Wang, Appl. Phys. Lett. 83, 2196 (2003).
[3] T. Maeda, T. Kai, A. Kiktsu, T. Nagase, J.-I. Akiyama, Appl. Phys. Lett. 80, 2147 (2002).