The Structure And Properties Of FePt-based Films

Due to its extremely large uniaxial magnetic anisotropy (Ku=～7×10-7ergs/cc), small grain size and high chemical stability, the L10-FePt film with face-centered tetragonal (001) texture has attracted great attention for the potential application in perpendicular recording media and magnetic tunnel junction. However, a subsequent anneal to form the L10 phase often result in undesirable dispersive grain size, irregular grain shape and random grain alignment. In this thesis, a kind of heat resisting continuous L10-FePt films suitable for microfabrication of arrays and a kind of hard/soft magnetic FexPt100-x composite with potential application to manufacture the cantilever for magnetic force microscope with high isotropic coercivity were prepared. The phase separation in FePt-Ag nanocomposites was also researched to understand the effect on the morphology. The surface morphology, magnetic properties and lattice structure were anylized.By magnetron sputtering, [Fe(0.6 nm)/Fe3o.5Pt69.5(1.9 nm)]10 continuous multilayer films with nominal composition of Fe5oPt5o and total thickness of 25 nm were deposited on MgO(001) substrates heated to 400℃, and then subjected to a vacuum annealing at temperatures in the range of Ta=[500,900]℃. The morphology, crystallography as well as magnetic property dependences of Ta were investigated by scanning electron microscope, atomic force microscope, X-ray diffraction and vibrating sample magnetometer. Heating the substrate during sputtering resulted in interlayer diffusion, and the as-deposited multilayer film showed the soft magnetic behaviors of FePt alloy with disordered A1 phase. Annealed at Ta％≥700℃, the film became the ordered L10 phase with significant (001) orientation; the ordering parameter was more than 0.85; the magnetocrystalline anisotropic energy exceeded 2.7×107 erg/cc. Due to the residual subtle periodical compositional fluctuation in the film, the ordering could nucleate interior the film and the Pt-enrichment boundaries were sufficiently suppressed. The continuity of morphology maintained at Ta≤800℃. The observation by atomic force microscope indicated that the film annealed at Ta=780℃had the flattest surface with sparse swells lower than 3 nm. This kind of heat-resisting continuous film would fit the need for microfabrication of patterned arrays of L10 FePt for applications such as the perpendicular magnetic recording media.FexPt100-x films (50 nm thick) with x=[10,85] in atomic percent were deposited by electron beam onto MgO (001) substrates heated to 100℃. And then the samples were annealed at 500℃ for 2 h. The crystalline structures and anisotropic magnetic properties were investigated. The direction of easy magnetization axis switches between horizontal direction and vertical direction with the increase of x, inducted by the intrinsic magnetocrystalline anisotropy and extrinsic shape anisotropy. At x=60, a composite of disordered A1 phase and ordered L10 phase can be obtained due to the unfinished A1→L10 transformation. Both the horizontal coercivity and the vertical coercivity exceed 5 kOe. The horizontal coercivity is higher than the magnetocrystalline anisotropic field of soft A1 phase, and the horizontal coercive loop is asymmetric. The mechanism is discussed by a tri-domain model for the hard-soft exchange coupling system. This kind of hard/soft magnetic composite has the potential application to manufacture the cantilever for magnetic force microscope with high isotropic coercivity.By magnetron sputtering, MgO (5 nm) underlayer and [(FePt(d nm)/Ag(3 nm)]n multilayer (d= 1,2,3,4; n= 9,5,3,2; the total thick of FePt film was d×n≈9; the total thick of Ag was 3n) were subsequently deposited onto quartz substrate heated to 100℃, and subjected to an anneal at 600℃for 30 min in vacuum. The vertical and horizontal coercivity is approximately 10 kOe, and the overlap of (002) peak and (200) peak is appeared in all samples. The addition of Ag can prevent the formation of L10-FePt, despite the fact that the MgO underlayer could induce the growth of (001) orientation. The film was phase-separated abruptly at d≤2. The phase separation significantly reduced the size of FePt grain. The Ag addition can decrease the exchange-coupling interaction among FePt grains.