M.L. Yan

Orientation-controlled nonepitaxial L10 CoPt and FePt films

We report results on highly oriented, face-centered tetragonal ordered CoPt and FePt thin films grown nonepitaxially by directly depositing films on thermally oxidized Si substrates and subsequent annealing. By controlling the thickness, composition, and annealing conditions, and/or depositing a proper underlayer, nearly perfect (001)-oriented CoPt and FePt films can be obtained. Magnetic measurements reveal large perpendicular anisotropy for such films.

Fabrication of nonepitaxially grown double-layered FePt:C/FeCoNi thin films for perpendicular recording

A noneptaxially grown double-layered thin-film medium of nanocompsite FePt:C with a FeCoNi soft underlayer for high-density perpendicular magnetic recording was fabricated and investigated. Square-shaped perpendicular loops with a remanance ratio nearly equal to one and a coercivity as large as 8.5 kOe were obtained for this ordered FePt:C double-layered medium. The formation of the ordered L10 phase is confirmed by electron diffraction experiments. Transmission electron microscope observations reveal that FePt grains with a uniform size less than 5 nm are embedded in the C matrix and appear to be well isolated. Our results show that nonepitaxially grown (001) textured double-layered nanocomposite L10 FePt-based films with perpendicular anisotropy are a promising candidate to realize extremely high-density perpendicular recording.

Highly oriented nonepitaxially grown L10 FePt films

A method of preparing nonepitaxially grown, highly textured L10 FePt thin films is described. A nearly perfect (001) texture was obtained by direct deposition of FePt films on Corning 7059 glass substrates and subsequent rapid thermal annealing. The ordering and orientation of the L10-phase FePt grains were controlled by the initial as-deposited film structure, and also by the annealing process. Magnetic measurements reveal large perpendicular anisotropy for these (001) textured films. The substrates and processes used for nonepitaxial growth of L10 ordered FePt films are much more compatible with practical applications than those grown epitaxially.

L10,(001)-oriented FePt:B2O3 composite films for perpendicular recording

A multilayered deposition structure was developed for fabricating FePt:B2O3 films. We successfully obtained nanostructured FePt:B2O3 films with FePt grains aligned perpendicular to film plane by postannealing the as-deposited multilayers at 550 °C for 30 min. It was found that development of (001) texture depends strongly on the total film thickness, initial B2O3 layer thickness, and Fe concentration. Nearly perfect (001) orientation of FePt-ordered grains can be obtained in the films with small total film thickness, large initial B2O3 layer thickness, and slightly higher Fe concentration. Our results show that highly (001) oriented films with ordered fct phase have significant potential as perpendicular media for extremely high-density recording.

High-anisotropy nanocomposite films for magnetic recording

This paper presents results on the synthesis and properties of FePt- and CoPt-based high-anisotropy nanocomposite films. These films consist of high anisotropy L1/sub 0/ CoPt or FePt particles embedded in a nonmagnetic matrix such as C, SiO/sub 2/, or B/sub 2/O/sub 3/. The grain size and magnetic properties of these films ran he controlled by the processing temperatures and the film compositions. Particularly in the FePt:B/sub 2/O/sub 3/ films the c-axes of the FePt grains can be made to align along the film normal direction, resulting in films with perpendicular anisotropy. Temperature-dependence of magnetic properties and activation volumes are investigated to understand the magnetization reversal and thermal-activation effects. The potential of these films as high-density recording media is discussed.

Effects of rapid thermal annealing on nanostructure, texture and magnetic properties of granular FePt:Ag films for perpendicular recording (invited)

We report effects of rapid thermal annealing on nanostructure, texture, and magnetic properties of granular FePt:Ag films. It was found that the orientations of FePt grains were dependent strongly on the as-deposited multilayer structure and the annealing processes. Through the control of the annealing processes, (001) textured L10 granular FePt:Ag films were obtained. Magnetic measurements revealed that saturation magnetization Ms, perpendicular coercivity Hc, and remanence ratio Mr/Ms, were also dependent on the annealing temperature, annealing time and Ag content. Perpendicular Hc values increased from 1.5 to 15 kOe when the annealing temperature changed from 400 to 600 °C for 600 s. Perpendicular Hc values remained about 11 kOe when the annealing time changed from 5 to 600 s. The effect of Ag content on magnetic properties is reported.

L1/sub 0/ 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 L1/sub 0/ phase is confirmed by XRD, and only visible (00l) 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. The FePt grains are very uniform with average sizes about 5 nm.

High-anisotropy nanocluster films for high-density perpendicular recording

This paper reports results on the synthesis and magnetic properties of L1/sub 0/:X nanocomposite films, where L1/sub 0/=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 highly (001) oriented L10 (Fe49Pt51)1−xCux 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 0to13at.%. All films were annealed at 600°C for 5min. 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 10nm. For FePt film with 11at.% Cu substitution, coercivity was about 5kOe, which is suitable for writing in a practical perpendicular-recording film.

Highly (001)-oriented Ni-doped L10 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(0.38nm)∕Ni(0.04nm)∕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 0.06nm, the coercivity is about 6kOe after annealing, which is suitable for the writing performance of high-anisotropy perpendicular recording media.