-FeCo multilayer film

The L1₀-type FeCo ordered phase exhibits large magnetic anisotropy, large magnetic moment, and high Curie temperature. Since L1₀-FeCo does not contain rare-earth elements, it is a potential candidate as a high-performance magnetic material [1]. On the other hand, the L1₀-FeCo system is at a non-equilibrium state, and its fabrication has been a challenge so far [2]. To overcome the problem, we inserted periodic buffer layers between the FeCo layers to maintain the L1₀ (fcc) structure [3]. For establishing the fabrication method of L1₀-FeCo, we here investigated the growth temperature (T_s) dependence of (7 ML-FeCo/3 ML-Ni buffer)₃ films fabricated by pulsed laser deposition.
The formation of the stable B2 (bcc) structure was suppressed at T_s = 450°C or lower. Although the formation of the fcc structure was confirmed, the L1₀-ordering was not recognized. Unfortunately, the spontaneous easy axis of magnetization in all the specimens was still the in-plane direction. However, the in-plane magnetization decreased at T_s = 300 and 450°C, and the magnetocrystalline anisotropy showed the maximum value for T_s = 300°C.

[1] T. Burkert et. al., Phys. Rev. Lett., 93, 027203 (2004).
[2] J. Shen et. al., Surf. Sci. Rep., 52, 163 (2004).
[3] H. Ito et. al., AIP Adv., 9, 045307 (2019).