Granular Structure And Magnetic Properties Of FePt Films

Magnetic recording materials have been applied in computer and electron devices. With the development of the electron industry, the area of single recorded bit becomes smaller and smaller. the recording area densities of magnetic recording material are demanded higher. The magnetic granular films are studied as a theme.FePt magnetic recording media as one kind of potential candidate for application of perpendicular magnetic recording has been investigated in this work. As we know, FePt has a strong magnetocrystalline anisotropy and a very high magnetic energy product, which make this kind of material suitable for ultra-high density perpendicular magnetic media.C/[FePt/C]10/C, Cr/[FePt/C]10/C and Ta/[FePt/Ta]5/Ta mutilayer films were successfully prepared by using RF and DC magnetron sputtering system. FePt nanoparticles embedded in C and Ta matrix were formed by consequently annealing. X-ray diffraction (XRD) results show the degree of atomic ordering of the L10 FePt phase. The ordering of the structure increases with higher annealing temperature. Magnetic measurements reveal that the values of in-plane coercivity (He) and squareness (Mr/Ms) depend on the thickness of carbon layer. High He (3245.1 Oe) and squareness (0.67) were obtained by annealing C/[FePt(2.5 nm)/C(2.0 nm)]10/C at 650?. The carbon not only isolates the FePt grains, but also suppresses the growth of the FePt grains. When the thickness of carbon layer is 2.0 nm, the FePt grain size decreases down to-20nm measured by Scan Probe Microscope (SPM). Interactions between particles can be tuned to near zero when we select the proper thickness of C layer. At the same time, the FePt/C samples with Cr underlayer were deposited. We found that Cr can refine the FePt nanoparticles. As for the sample of Ta/[FePt(2.5nm)/Ta(2.5 nm)]5/Ta annealed at 650?, we got higher He (6828.4 Oe) and squareness (0.80559). When the thickness of Ta layer is 2.5nm, the FePt grain size decreases down to ?20 nm measured by SPM. The reversal process of FePt thin films has been investigated by measuring the activation volume and real grain volume. The rotation of the magnetization is dominated in the reversal process of FePt thin film, the [FePt(2.5 nm)/Ta(2.5 nm)]5 mutilayer films annealed at 650?, The c/a value of FePt grains is about 0.967. It is close to the value of the equiatomic L10 FePt structure. It shows that the sample has already had the atomic ordering of the L10 structure.