Improving magnetic properties of FeCrCo films by facilitating the internal α-γ phase transition through Pt diffusion

Abstract

FeCrCo magnetic films are suitable candidates for use as magnetic code disk materials in high-accuracy magnetic encoders. The performance and material uniformity of FeCrCo films are crucial for high-accuracy servo control of the encoder. However, enhancing coercivity and maintaining material uniformity while ensuring sufficient remanence in FeCrCo films pose challenges. Herein, Pt (t nm)/FeCrCo (100 nm) films were prepared via magnetron sputtering and subsequent vacuum annealing. The remanence of the FeCrCo (100 nm) monolayer film is 520 emu/cm3, with a coercivity of only 380 Oe. However, after using Pt as the buffer layer, the remanence of Pt (1 nm)/FeCrCo (100 nm) and Pt (2 nm)/FeCrCo (100 nm) films is 320 emu/cm3 and 250 emu/cm3 respectively, while the coercivity increases to 520 Oe and 625 Oe respectively, representing improvements of 37 % and 65 %. This significant increase in coercivity is achieved with the remanence still meeting the performance requirements of the magnetic code disk. High-resolution transmission electron microscopy (HRTEM) analysis reveals that diffused Pt atoms can facilitate the formation of a small amount of non-magnetic γ-FeCrCo phase, which has a pinning effect on magnetic domain walls, thus significantly increasing the coercivity of the FeCrCo film. Moreover, since the γ-FeCrCo phase and the α-FeCrCo phase have similar crystal lattices, material uniformity can be maintained, which is beneficial for ensuring the uniformity of output signals of the code disk with small magnetic pole pitches.