L1\u3csub\u3e0\u3c/sub\u3e Ordered FePt:C Composite Films With (001) Texture

Highly textured (001) FePt:C nanocomposite thin films, deposited directly on thermally oxidized Si wafers, are obtained by multilayer deposition plus subsequent thermal annealing. Nanostructures, crystalline orientations, interactions, and magnetic properties are investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), magnetic force microscopy, and magnetic measurements. The formation of the ordered L10 phase is confirmed by XRD, and only visible (00 ) peaks indicate a high degree of the (001) texture. TEM observation reveals that FePt grains are embedded in the C matrix and appear to be well isolated

Nanostructure and magnetic properties of highly (001) oriented \u3ci\u3eL\u3c/i\u3e1\u3csub\u3e0\u3c/sub\u3e (Fe\u3csub\u3e49\u3c/sub\u3ePt\u3csub\u3e51\u3c/sub\u3e)\u3csub\u3e1-x\u3c/sub\u3eCu\u3csub\u3ex\u3c/sub\u3e films

We report on nonepitaxially grown L10 Cu-alloyed FePt thin films with strong (001) texture. The FePt films with different Cu contents were deposited directly on Si wafers with a Fe49Pt51/Cu multilayer structure. The Cu content was varied from 0 to 13 at. %. All films were annealed at 600 °C for 5 min. X-ray-diffraction characterization showed that only one set of L10 diffraction peaks appeared and no elemental Cu diffraction peaks were visible. This result, along with a varying c/a lattice-parameter ratio, suggests that Cu substitutes Fe or Pt in the L10 lattice and ternary FePtCu alloy films are formed. (001) texture was enhanced with the increase of Cu content. Transmission electron microscope images showed that the grain size of FePtCu was about 10 nm. For FePt film with 11 at. % Cu substitution, coercivity was about 5 kOe, which is suitable for writing in a practical perpendicular-recording film

Dissociative electron attachment to vibrationally and rotationally excited H\u3csub\u3e2\u3c/sub\u3e and HF molecules

The vibrational and rotational state dependence of dissociative attachment (DA) in low-energy e-H2 and e-HF collisions is studied within the framework of nonlocal resonance theory. The dynamics of nuclear motion in the nonlocal complex potential is treated by the quasiclassical approach. The resonance energy, width function, and level-shift function are taken from our previous calculations based on the projection operator formalism. Results for all vibrational states up to the dissociative attachment thresholds and selected rotational states are presented. Our cross sections for H2 exhibit a plateau structure in the energy range above the dissociation threshold, and this structure gets more pronounced with higher v or J. The dissociative attachment cross section for vibrationally and rotationally hot HF (T=1150 K) agrees well with available experimental data. For H2 in thermal equilibrium at 1400 K, the agreement between experiment and theory is less satisfactory

High-Anisotropy Nanocluster Films for High-Density Perpendicular Recording

This paper reports results on the synthesis and magnetic properties of L10:X nanocomposite films, where L10 = FePt, CoPt, and X = C, Ag, etc. Two fabrication methods are discussed: nonepitaxial growth of oriented perpendicular media, and monodispersed nanoparticle-assembled films grown with a gas-aggregation source. The magnetic properties are controllable through variations in the nanocluster properties and nanostructure. The films show promise for development as recording media at extremely high areal densities

Nanostructure and Magnetic Properties of FePt :C Cluster Films

Magnetic properties and nanostructure of FePt : C cluster-deposited films with C volume fraction of 7%, 14%, 33%, and 45% have been studied. As-deposited FePt : C films were prepared by a multilayer method in which FePt layers were deposited from a cluster source employing a gas-aggregation technique and C layers from a normal sputtering gun. In the as-deposited films, FePt clusters with fcc structure are embedded in the C matrix. The high anisotropy FePt L10 cluster structure was realized in the films via post-deposition annealing and the nanostructure of the films was observed by high-resolution transmission electron microscope (TEM). The results for a film with 45 vol. % C showed that FePt clusters are well separated by C matrix and the cluster diameter is about 4.5 nm. The coercivity increases with increase of annealing temperature; coercivities larger than 9 kOe were achieved in the films after annealing at a temperature of 700 ºC and above. Magnetization reversal of the films was studied by moment-decay measurements and the data were fitted with the Sharrock formula. For the film with 45 vol. % C annealed at 625 ºC, the thermal stability factor KuV*/kB, T activation volume V*, and anisotropy constant Ku are 231, 0.83 ×10-18cm3 and 1.2 ×107 erg/cm3, respectively

Cluster-Assembled Nanocomposites

This chapter focuses on a gas-aggregation technique to prepare magnetic nanoclusters with controllable cluster sizes and size distributions. The review includes current research on nanoclusters, such as uncoated and oxide-coated Fe, Co and Fe clusters and clusters made from alloys, but special emphasis is on highly anisotropic L10-ordered FePt clusters, which are of potential interest for magnetic recording with ultrahigh areal densities of more than 1 Tera bit/in2. In particular, we discuss magnetic and structural properties of FePt nanoclusters and thin films. Another approach discussed in the chapter is to create cluster nanocomposites by multilayering with post-deposition annealing. The advantage of this method is that the clusters can be oriented along a desired easy axis. One example is L10-(001) oriented FePt nanocomposite films with a FePt cluster size of about 5 nm

Continuous/Cluster-Pinned Recording Media

We propose and theoretically investigate a new class of nanostructured magnetic recording films, cluster-pinned recording media. The films consist of magnetic clusters exchange coupled to a continuous hard layer with perpendicular anisotropy and low coercivity. Our calculations yield the coercivity and the cross-track correlation length as a function of film thickness and pinning density and strength. The mechanism is very similar to the Gaunt–Friedel pinning in bulk magnets, which differs from ordinary strong pinning by the selfconsistent dependence of wall curvature and coercivity on defect concentration. The main difference is the exponent for the coercivity as a function of the pinning strength, which is equal to 2 in the bulk but equal to 3/2 in thin films. The pinning strength is estimated for various regimes, and it is shown that the diminished domain-wall curvature reduces jitter

Magnetic properties of \u3ci\u3eL\u3c/i\u3e1\u3csub\u3e0\u3c/sub\u3e FePt and FePt:Ag nanocluster films

A sputtering gas-aggregation technique has been used to prepare FePt and FePt:Ag nanocluster films. The cluster size was controlled in a range from 3 to 6 nm. FePt cluster films were directly deposited onto Si substrate; FePt:Ag cluster films were fabricated by depositing a FePt cluster layer between a Ag underlayer and overlayer. Nanostructure and magnetic properties of the samples were characterized by x-ray diffraction, transmission electron microscopy, and magnetometry. The high magnetic anisotropy L10 fct phase was realized in the films annealed at a temperature of 550 °C and above. The orientation of clusters is random. The coercivity increases with an increase of annealing temperature; high in-plane and out-of-plane coercivities, exceeding 10 kOe, were achieved in both FePt and FePt:Ag cluster films after annealing. For FePt:Ag films, the coercivity increases with Ag underlayer thickness, tAg, and reaches about 17 kOe at room temperature for tAg = 5 nm after annealing at 650 °C for 10 min. The high coercivity is closely correlated with the degree of L10 ordering and nanostructure of the films

Highly (001)-oriented Ni-doped \u3ci\u3eL\u3c/i\u3e1\u3csub\u3e0\u3c/sub\u3e FePt films and their magnetic properties

We report on Ni-doped nonepitaxial L10 FePt thin films with strong (001) texture. The influences of Ni doping on L10 ordering, orientation, and the magnetic properties of the FePt films have been investigated. In-plane and out-of-plane x-ray diffractions (XRD) were used to analyze the texture of FeNiPt films. For [Fe(0.38 nm)/Ni(0.04 nm)/Pt(0.4)] 13 sample, the out-of-plane XRD data showed only (00l) peaks and in-plane data showed (hk0) peaks after annealing, indicating high (001) texture of the FeNiPt films. In comparison with FePt, the (00l) peak positions shifted to higher angle, indicating partial Ni substitution in the L10 lattice. The coercivity, measured at room temperature, decreased as a function of Ni doping. For the film with a Ni layer thickness of 0.06 nm, the coercivity is about 6 kOe after annealing, which is suitable for the writing performance of high-anisotropy perpendicular recording media