FePt Grains Research Articles

Permanent-magnet properties of thermally processed FePt and FePt-Fe multilayer films

FePt single-layer and FePt-Fe multilayer thin films are prepared by magnetron sputtering. By varying the Pt content, FePt, Fe/sub 3/Pt, or a mixture of FePt and Fe/sub 3/Pt can be obtained in Fe-Pt single layers. In annealed FePt-Fe multilayers, the coercivities decrease with the introduction of Fe layers compared to FePt single layers, while the magnetization increases. The single-phase behavior of the hysteresis loops of FePt-Fe multilayers indicates the existence of exchange coupling in these materials. For one FePt-Fe sample with optimized exchange coupling, the intrinsic properties correspond to an energy product of 19 MGOe. The texture of the magnets is determined by the [111] orientation of the crystallites. This means that the easy magnetization directions of the FePt grains form an angle of 54.7/spl deg/ with the film normal, but are randomly oriented in the film plane. It is analyzed how this easy-axis distribution affects the magnetic hysteresis.

Structural and Magnetic Properties of FePt and FePt-Al2O3 Thin Films

The magnetic and structural properties of FePt and FePt-Al2O3 films deposited by rf-sputtering on 7059 corning glass substrates were investigated. The coercivities of the films can be adjusted from 20 to 12.3 kOe through controlling the ordering degree of the FePt phase. With the increasing annealing temperature TA from 100 to 650 degreesC, the average grain size of FePt grains increased from about 10 to 50 nm in the FePt films, while it kept almost a constant of about 10 nm in the alumina-added films. The measurements of the deviation Deltam*(H) as a measure for particle-particle interaction and SFD (switching field distribution) revealed that the addition of alumina contributed to diluting the intergranular exchange coupling interaction. In the case of the FePt-Al2O3 (25 vol%) films with varying film thickness from 20 to 180 nm annealed at 550 degreesC for one hour, no obvious changes in structural and magnetic properties due to the variation of film thickness was detected. Grain size was in the vicinity of 10 nm, squareness S about 0.9, coercivity squareness S-* almost a constant of about 0.85, and the in-plane coercivities kept high value of about 5.5 kOe.

Microstructure and magnetic properties of nanocomposite FePtCr–SiN thin films

[ (FePt) 100−x Cr x ] 100–δ –[ SiN ] δ nanocomposite thin films with x=0–25 at. %, and δ=0–30 vol. % were fabricated on a natural-oxidized Si(100) substrate by dc and rf magnetron cosputtering of FePt, Cr, and Si3N4 targets. The thickness of the films was kept at 10 nm in order to examine the possibility for applying in high-density magnetic recording media. Transmission electron microscopy (TEM) and electron diffraction analyses indicated that the face-centered-cubic (fcc) γ-phase FePt, body-centered-cubic (bcc) Cr, and amorphous SiN coexisted in as-deposited films. The as-deposited films were annealed in vacuum between 350 and 750 °C for 30 min, and then ice-water quench cooling, in order to transform the soft magnetic fcc γ-FePt phase to the hard magnetic face-centered-tetragonal (fct) γ1 phase. Cr was added to inhibit the FePt grain growth, and was observed by TEM and energy disperse spectrum analysis in the grain surface area of FePt grains. The TEM observation indicated that the structure of the film was an amorphous SiN matrix with FePtCr particles dispersed in it. The particle size of FePtCr in annealed film was increased with the annealing temperature but decreased with the increase of SiN and Cr contents. Magnetization measurements indicated that the optimum condition for high-density magnetic recording purpose of the film was found with x=10 at. % and δ=15 vol. %, annealing at 600 °C for 30 min. The average grain size of the FePtCr in this film is about 9.5 nm, the saturation magnetization is 450 emu/cm3, in-plane coercivity is 3.7 kOe, and in-plane squareness is about 0.75.

FePt–Ag nanocomposite film with perpendicular magnetic anisotropy

Magnetic properties of FePt–Ag nanocomposite films synthesized by annealing (FePt/Ag)n multilayers deposited on a MgO(100) substrate by laser ablation are discussed in conjunction with the structure. After annealing over a temperature range from 540 to 650 °C, a large perpendicular magnetic anisotropy constant Ku of the order of 107 erg/cc developed. The so-called δM curve measurements imply that grains are magnetically decoupled. Increasing the Ag layer thickness is found to be useful for the improvement of the (001) orientation of FePt grains. The remanence ratio and coercivity increase with a rise in the annealing temperature. Magnetic grains of less than 10 nm and a small activation volume of the order of 10−19 cm3 are observed.

L 1 ,(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.

Ordering of island-like FePt L1 thin films

We report the island growth morphology of 50-nm-thick FePt thin films prepared on MgO substrates by dc magnetron sputtering. In-depth high-resolution transmission electron microscopy studies showed that the island had a very flat facet in a dome shape and was composed of two distinct structures. The island contained FePt grains with an average size of 5–7 nm within about 10 nm from the film surface, whereas an ordered L10 phase was established below the island. The L10 structure was compressively strained along the film plane, generating {111} twins and stacking faults. The strained structure also affected the region where agglomeration between islands occurs.

FePt/BN granular films for high-density recording media

FePt particles with the high magnetocrystalline anisotropy L1 0 structure and particle sizes between 3 and 15 nm have been fabricated by annealing FePt/BN multilayers with bilayer thicknesses in the range of 2.5–200 Å, at 600°C and 700°C. Films with thicker bilayer thicknesses were found to have a strong (1 1 1) texture, which is less developed in thinner bilayer films. For a particular bilayer thickness (FePt-20 Å/BN-40 Å), a special type of textured ordering is observed in the X-ray diffraction patterns, in which the c-axis of all the particles has a perpendicular component. Magnetic measurements showed that a wide range of coercivities (2–18 kOe) could be obtained in the films by varying the bilayer thickness and the annealing temperature and time. The concentration of BN was found to control the interparticle interactions, which for certain BN values led to decoupling of the FePt grains.

Ｂｉ下地によるＦｅＰｔ規則相の低温合成

We investigated the L10 ordering process of FePt films deposited on a Bi underlayer. When annealed at relatively low temperatures, Bi tends to move toward the surface of an FePt layer. It was found that Bi travels along the grain boundary of FePt. This accelerates coalescence of FePt grains with intensive atomic diffusion, which leads to faster transformation from the disordered phase to the ordered. Subsequent rapid increase of coercivity is observed after annealing at 350°C. This appreciable reduction of ordering temperature may remove the difficulty of fabrication of L10-type, high-density recording media.

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.

Nanostructured FePt:B2O3 thin films with perpendicular magnetic anisotropy

FePt/B 2 O 3 multilayers were deposited by magnetron sputtering onto 7059 glass substrates. By annealing the as-deposited films at 550 °C, nanostructured FePt:B2O3 films consisting of FePt grains with L10 structure, embedded in a glassy B2O3 matrix, were obtained. The c axes of the FePt grains can be made to align with the film normal direction, which results in a perpendicular anisotropy constant of 3.5×107 erg/cc. The films remain layered structures after annealing when the B2O3 layer thickness exceeds 16 Å. The nanostructure of the films was investigated by transmission electron microscopy. The coercivities and the average grain sizes of the films are dependent on the B2O3 concentrations, with coercivities varying from 4 to 12 kOe, while average grain sizes vary from 4 to 17 nm. Strong perpendicular anisotropy, adjustable coercivity, and fine grain size suggest this nanocomposite system might have significant potential as recording media at extremely high areal density.

7317. Recrystalline and grain growth phenomena in polycrystalline Si/CoSi 2 thin-film couples : S Nygren and S Johansson, J Appl Phys, 68, 1990, 1050–1058

The high magnetocrystalline phase of L10 FePt has received considerable attention for achieving stable magnetization states in small volumes which could increase magnetic areal storage densities. When FePt is sputter-deposited, it adopts a magnetically soft A1 phase requiring annealing to phase transform to the L10 phase; this annealing results in detrimental grain growth which reduces the capacity for high areal storage densities. In the current work, a series of 10 nm thick granular FePt–SiO2 thin films with various silica contents has been annealed at different fluences using a 10 ms pulse width, 1064 nm wavelength laser to determine if the silica matrix could inhibit this grain growth. The A1 to L10 phase transformation was confirmed by selected area electron diffraction. In general, the films annealed with approximately 25 J/cm2 exhibited the highest L10 c/a tetragonality, 0.97, and coercivity of approximately 875 kA/m (11 kOe). For these films, the 38 vol.% silica incorporation resulted in a FePt grain size of approximately 8.5 nm as compared to 30 nm for films with no silica. The granular encasement of the FePt grains was effective at reducing but unable at inhibiting grain growth using single pulsed laser anneals.