Shintaro Hinata

Uniaxial magnetocrystalline anisotropy for c-plane oriented Co100−xMx (M: Cr, Mo, W) film with stacking faults

Stacking faults (SFs) in Co-based alloy grains in a Co100−xMx (M: Cr, Mo, and W) film are evaluated by means of in-plane x-ray diffraction. Moreover, the correlation between SFs and uniaxial magnetocrystalline anisotropy Ku is discussed in connection with the spin-orbit interaction. The ratio of the integrated intensities of the (10.0) to (11.0) diffractions corrected by Lorentz and atomic scattering factors has been proposed as an index for SFs in hcp films with a c-plane sheet texture. This ratio is equal to 0.25 for perfect hcp stacking, while it is 0 for perfect fcc specific stacking. It has a one-to-one correspondence with the probability of -A-B-C- atomic-layer stacking Pfcc. Using this index, pure sputtered Co films are found to have a Pfcc of 10%. The addition of only 5 at. % of Mo or W into the Co grains reduces Pfcc to 2%. Ku was found to increase with the addition of material (e.g., Ku was 4.0×106 ergs/cm3 for 5 at. % Mo), although the atomic magnetic moment of Co decreases monotonously. A Pfcc...

Giant negative uniaxial magnetocrystalline anisotropy of Co80Ir20 sputtered films with perfect hexagonal-close-packed and composition-modulated atomic layer stacking

Co80Ir20 films with negative uniaxial magnetocrystalline anisotropy (Ku) are investigated with respect to the regularity of the stacking sequence and atomic site arrangement. Substrate heating at 600 °C enhances the negative Ku of Co80Ir20 to −9.6 × 106 erg/cm3. X-ray diffraction analysis and scanning transmission electron microscopy of the Co80Ir20 film fabricated at 600 °C indicate (1) a near perfect hexagonal-close-packed (hcp) stacking structure and (2) an atomic layered structure that consists of randomly sequenced Ir-rich and Ir-poor layers. These hcp and composition-modulated atomic layer stacking structures are considered to be the reason for the enhancement of the negative Ku.

Q-band ferromagnetic resonance for CoPt-based stacked perpendicular recording media with interlayer exchange coupling

The ferromagnetic interlayer exchange coupling Jinter for stacked perpendicular recording media with a granular layer (GL)/interlayer (IL)/alloy capping layer (CL) structure was quantitatively evaluated by Q-band ferromagnetic resonance (FMR). Two resonances with acoustic and optical precession modes were observed in the FMR signals from the stacked media. Fitting using the Landau–Lifshitz–Gilbert (LLG) equation indicated that Jinter increased from 0.55 to 1.83 erg/cm2 when the Pt IL thickness was reduced from 2.0 to 1.0 nm for media based on Co82Cr10Pt8-CL (4 nm) and Co74Pt16Cr10-8 mol (SiO2)-GL (16 nm). The optimum Pt IL thickness at which the switching field distribution was minimized due to a large reduction in the saturation field of the stacked media was found to correspond to the boundary condition between antiparallel and parallel precession of the magnetic moments of the GL and CL in FMR.

Ferromagnetic resonance analysis of internal effective field of classified grains by switching field for granular perpendicular recording media

The internal effective fields Heff of granular perpendicular magnetic recording media with a switching field (SF) distribution were measured by ferromagnetic resonance (FMR) by sweeping the external field HDC. Heff consists of the anisotropy field Hk, the dipole interaction field, the self-demagnetization field, and the intergranular exchange (coupling) field Hex for up and down magnetic moments of magnetic grains classified by their SF. Prior to the measurement, magnetic grains were classified into two classes: Those with high and low SFs when HDC is swept from +18 kOe to a negative field. FMR measurements were performed in a range for which the same domain structure was retained for typical strong and weak intergranular exchange coupled media (media I and II, respectively). These measurements revealed the following points. (1) Resonances originating from majority-direction moments were observed, whereas those of minority-direction moment were not. (2) The increase in Heff with decreasing 4πM for medium ...

Evaluation of Atomic Layer Stacking Structure and Curie Temperature of Magnetic Films for Thermally Assisted Recording Media (Invited)

Thermally assisted recording system is a promising candidate to overcome the trilemma of perpendicular magnetic recording hard disk drive development. In this paper, we introduce our current research about evaluation for the media material. In-plane X-ray diffraction technique is effective to evaluate atomic layer stacking structure of (111)-oriented face-centered cubic, c-plane-oriented hexagonal closed packed (hcp), and their intermediate structure with stacking faults of CoPt alloy thin film. Analytical results of Co50Pt50-based thin film shows that changing the valence electron number closer to 9 can effectively reduce the stacking fault. In practical, perfect hcp atomic layer stacking can be achieved by substituting Pt (group 10) with Rh (group 9). High-angle annular dark field of scanning transmission electron microscopy with probe diameter of 1 Å can effectively observe composition modulated atomic layer stacking with the super-lattice diffraction in Co-based alloy films. In practical, for Co80M20 (M: Ir, Pt) thin film sputtered under high substrate temperature, the irregular or alternately layered structure of M rich and M poor layer can be observed directly. To evaluate Curie temperature (TC), which is an important physical property of thermally assisted media, conduction electron spin-dependent scattering should be the focus. Fitting dielectric spectra for MnSb thin film with TC ~ 320°C measured with the ellipsometry and analyzing the Drudes term, temperature dependence of resistivity and scattering time at around TC was confirmed.

Successful fabrication of high Ku columnar CoPt-SiO2 granular film sputtered under high substrate temperature

High substrate temperature sputtered CoPt-SiO2 granular films with columnar grain structure, high perpendicular uniaxial magnetic anisotropy (Ku⊥), and low stacking faults (SFs) are reported. By introducing a CoCr-SiO2 buffer layer onto a Ru layer, SiO2 segregates to Ru grains boundaries and CoCr grains grow epitaxially onto Ru grains. Consequently, the bumpy surface morphology of the underlayer is maintained even though the temperature of the substrate heating is subsequently elevated to around 400 °C. Therefore, the CoPtCr magnetic grains of the CoPtCr-SiO2 granular recording layer can grow epitaxially with columnar structure upon the CoCr grains of the CoCr-SiO2 buffer layer. For deposition of CoPt-SiO2 (no Cr) granular films at the substrate temperature below 400 °C, the increase of SFs can be suppressed such that Ku⊥ can be kept high at around 6.5 × 106 ergs/cm3 (Kugrain of around 9.0 × 106 ergs/cm3, where Kugrain is referred to uniaxial magneto-crystalline anisotropy of the magnetic grains when oxid...

High Ku and small grain size Co80Pt20 granular media with double oxide grain boundary materials consisting of B2O3

Investigation of magnetic properties and microstructure of granular media with various double oxides including B2O3 as the grain boundary material is reported. By adding a high Tm second oxide together with B2O3 for the grain boundary material, comparable magnetic properties with that of the single oxide granular media and smaller crystallite size evaluated by X-ray diffraction (GDinplane) than that of the single oxide granular media can be obtained. Among the evaluated media, the granular medium with B2O3− TiO2 is promising for the grain boundary material, showing comparable average Ms and Ku of 806 emu/cm3 and 7.7×106 erg/cm3 with that of the single B2O3 and smaller GDinplane of 4.8 nm than that of the single B2O3 of 5.4 nm. In the TEM image, thin grain boundaries inside the grains can be observed which indicates that small grains with one-on-one grains growth is expected when an underlayer with smaller grain size is utilized.

High

Magnetic properties and microstructure of Co₈₀Pt₂₀-30 vol.% (Al₂O₃, TiO₂, WO₃) and Co_82.4Pt_17.6-27.7 vol.% SiO₂ granular films postannealed at various temperatures in a heat-treating furnace were investigated. In this paper, it is found that among these granular films, CoPt-WO₃ granular film shows the highest coercivity (H_c) because of low intergranular exchange coupling of well-isolated magnetic grains. Furthermore, the H_c is enhanced with postannealing because of the increase of the magnetic anisotropy field (H_k^grain) and uniaxial magnetocrystalline anisotropy (K_u^grain) of the columnar growth magnetic grains. The increase of K_u^grain for the postannealed granular film primarily originates from the reduction of the stacking faults as well as the lattice constant ratio.

K_{{{u}}}

A new method for evaluating the switching field distribution (SFD) in perpendicular magnetic recording media is proposed using the saturation magnetic field of a minor loop, Hsminor. In this method, the switching fields of focused reversal magnetic domains are measured with all magnetic moments in other domains saturated in the upward direction. Thus, the proposed SFD evaluation is not affected by variety of domain structure, and reveals tails of distribution. Using the proposed method, the SFD for various granular media was evaluated.

and Low Intergranular Exchange Coupling of Postannealed CoPt-WO 3 Granular Film

The magnetic properties and structures of Co80Pt20–30 vol % oxide (ZrO2, Cr2O3, Y2O3, Al2O3, MnO, TiO2, WO2, SiO2, Mn3O4, WO3, Co3O4, MoO3, and B2O3) granular media deposited at room temperature were investigated. As a result, the following were found. 1) By employing oxides with low melting point temperatures as the granular media, magnetic grains with high saturation magnetization () and perpendicular magnetic anisotropy () are obtained; the increases in and are due to the promotion of the columnar growth of magnetic grains and phase separation or two-phase precipitation between magnetic grains and oxides. 2) The increase in the of the granular media followed by the decrease in the melting point of oxides is due to the reduction in the amount of stacking faults. 3) Among these granular media, the CoPt–B2O3 granular medium has the highest coercivity (H c) and ratio of H c to the magnetic anisotropy field () of 8.0 kOe and 0.4, with and of 1115 emu/cm3 and 1.1 × 107 erg/cm3, respectively. 4) The CoPt–B2O3 granular medium has well-isolated and columnar growth magnetic grains with an average grain size of 6.5 nm.