L1₀ Ordering Control In FePt Thin Films

Since L1₀ ordered FePt crystal has a very high magnetocrystalline anisotropy energy density, FePt thin films are considered to be potential candidates for ultrahigh density magnetic recording media. The high ordering temperature, however, is unfavorable for the practical application. So how to accelerate the ordering process and reduce the ordering temperature of FePt thin films are of great significance to promote its practical application. Therefore, it needs to explore some new technologies to lower the ordering temperature of FePt thin film. In this paper, the subjects about the reduction of the ordering temperature of FePt thin films were studied by two aspects as following.We compared the ordering process of FePt films with different Ni₃Al thicknesses annealed at 380℃by the introduction of a thin Ni₃Al interface layer between FePt thin films and Si/SiO₂ substrates. And then we employed X-ray diffraction (XRD), transmission electron microscopy (TEM) techniques. The results indicate that the coercivity Hc=1.56 kOe and the ordering degree S=0.54 for the FePt thin film deposited on Si substrates with 1.7 nm Ni₃Al interface layer annealed at 380 oC are much higher than that Hc=0.7 kOe and S=0.35 for the films deposited on Si/SiO₂ substrates annealed at the same temperature.This indicats that the ordering process of FePt thin films was obviously promoted by the introduce of the Ni₃Al interface layer. The ordering degree is improved with the increase of the thickness of Ni₃Al interface layer,and yields the peak when the thickness of Ni₃Al layer was 5nm.The accelerated ordering of the FePt thin films by the existence of Ni₃Al interface layer may result predominantly from the formation of a stress on the films during annealing process which was induced by the difference of the thermal expansion coefficients between FePt films and Ni₃Al interface layer, which promotes the atom transmission in FePt thin films.The grain size of the as-deposited FePt thin film is reduced to das=3.5 nm, keeping on the same ingredient of FePt thin films by the change of the sputtering pressure and the control of the ratio of the Fe and Pt in the composite FePt target. The results indicate the ordering process of FePt thin films is promoted by the increase of the grain boundaries.The accelerated ordering of the FePt thin films with the increase of the grain boundaries may be attributed to the enhanced nucleation number of the L1₀ ordered domains by the increase of the atomic diffusion which owe to the increase of the grain boundaries induced by the reduction of the grain size.