Norikazu Itagaki

Improvement of magnetic properties of granular perpendicular recording media by using a fcc nonmagnetic intermediate layer with stacking faults

Various binary systems are investigated as face-centered cubic (fcc) bases for the nonmagnetic intermediate layer (NMIL) in granular perpendicular recording media. Loss of stacking order on the (111) plane in fcc NMIL is found to enhance the perpendicular magnetic anisotropy energy (KuRL) of the overlying medium. One persuasive reason for this enhancement is the preferred epitaxial growth of magnetic grains on only the (111) atomic terrace of the fcc NMIL due to collapse of the sixfold symmetry of (1¯11), (11¯1), and (111¯) atomic terraces of the fcc NMIL.

Pseudo-hcp nonmagnetic intermediate layer for granular media with high perpendicular magnetic anisotropy

Materials with the hexagonal close-packed structure (hcp) and the face-centred-cubic structure with stacking faults (pseudo-hcp) are examined for the nonmagnetic intermediate layer (NMIL) in order to suppress variant growth of magnetic grains for granular-type perpendicular recording media. Judging from the analysis of the epitaxial growth of Co-based magnetic grains, it has been found that a lattice misfit between NMIL and magnetic grain of less than 6% and a spreading coefficient of wettability of magnetic grain on NMIL of greater than 0.3 J m−3 are required for the recording layer to have high perpendicular magnetic anisotropy energy.

Improvement of magnetocrystalline anisotropy of columnar structure for epitaxially grown CoCr-based perpendicular media

To improve uniaxial magnetic anisotropy Kugrain of c-plane-oriented columnar grains for CoCr-based perpendicular recording media, an epitaxial growth technique has been applied. The main results are as follows. (1) Using a Ru(3 nm) or Co60Cr40(20 nm)/C(1 nm) intermediate layer, Kugrain for a Co69Cr19Pt8B4 medium was enhanced from 2.04×106 erg/cm3 to 2.53×106 erg/cm3 or to 2.76×106 erg/cm3, respectively. (2) The enhancement of Kugrain depends on the composition of the magnetic layer when using the Co60Cr40/C intermediate layer. (3) The epitaxial growth technique is also effective to increase KugrainVact/kT. Especially, in the media with a high concentration of B or Cr, the thermal stability is improved mainly due to an increase of Kugrain rather than an enlargement of Vact.To improve uniaxial magnetic anisotropy Kugrain of c-plane-oriented columnar grains for CoCr-based perpendicular recording media, an epitaxial growth technique has been applied. The main results are as follows. (1) Using a Ru(3 nm) or Co60Cr40(20 nm)/C(1 nm) intermediate layer, Kugrain for a Co69Cr19Pt8B4 medium was enhanced from 2.04×106 erg/cm3 to 2.53×106 erg/cm3 or to 2.76×106 erg/cm3, respectively. (2) The enhancement of Kugrain depends on the composition of the magnetic layer when using the Co60Cr40/C intermediate layer. (3) The epitaxial growth technique is also effective to increase KugrainVact/kT. Especially, in the media with a high concentration of B or Cr, the thermal stability is improved mainly due to an increase of Kugrain rather than an enlargement of Vact.

Effective Switching Field Distribution Evaluation Using Saturation Field in Minor Loop

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.

Diffusion analyses of non-ferromagnetic element in the cap-Layer of post-annealed CoCrPt perpendicular media

This paper reports on the factors that dominate diffusion phenomena in post-annealed CoCrPt media with various cap-layer elements X. Hf- and Zr-capped media were found to show low diffusion temperature and have thin reacted layer in this experiments. These results are explained with following relationships revealed by detailed analyses of boundary diffusion and interdiffusion: 1) X with high melting point in cap-layer hardly starts boundary diffusion and interdiffusion, 2) X-capped media with higher melting point of CoX compound forms thinner reacted layer, and 3) X with low enthalpy of Co-X formation lead to low diffusion temperature.

Improvement of perpendicular magnetic properties by postannealing for M'-CoCrPt-M stacked media (M, M'=Ti, Ta, Ru, Pt, CrMn, MnSi)

In this paper, we discuss the effect of postannealing on magnetic properties and microstructure for CoCr-based perpendicular recording media. Material investigation for cap- and under-layers of the postannealed media is carried out, and significant improvement of magnetic properties is confirmed for the media with both titanium cap- and under-layers. This is caused by decoupling of magnetic exchange interaction among grains due to diffusion of Ti into the grain boundaries and by elimination of the nanocrystalline initial layer that behaves like a soft magnetic layer.

Characterization to realize CoCr-based perpendicular magnetic recording media with high squareness and normalized coercivity

In an attempt to find a material guidance to realize CoCr-based perpendicular media with high squareness and normalized coercivity, we have performed systematic magnetic characterization to examine the effects of thermal agitation and magnetic exchange interaction. The main results are as follows: (1) With decreasing measuring temperature from R. T. to 4.2 K, normalized coercivity, Hc/Hkgrain, increases for the medium strongly influenced by thermal agitation, whereas changes slightly for the medium with strong intergranular exchange coupling. (2) All the media characterized in this study have a low value of Hc/Hkgrain equal to or less than 0.36 at R. T. (3) An exchange decoupled medium (α=1.0) tends to show a large positive Hn/Hkgrain, which results in a significant decrease of loop squareness S. On the other hand, it is possible to obtain a medium with S=1 for α>1.6 through the exchange interaction. (4) To realize a medium with S=1 and α as small as possible, selection of material with 4πMs/Hkgrain=0.2 (...

4.8?nm diameter Ru grains grown on a large-grain seed layer for perpendicular magnetic recording media

A concept for the non-magnetic intermediate layer (NMIL) is proposed, which realizes a recording layer of small and highly c-plane oriented grains with no inter-granular exchange coupling. The NMIL consists of three individual epitaxially grown functional layers: a large-grain seed layer (SL) with a highly oriented sheet texture, a first inter-layer (IL1) of small grains and a second inter-layer (IL2) of segregated non-magnetic grains. On focusing on the wettability and the lattice misfit of Ru IL against the SL material, the Mg SL is found to realize the small Ru grains of 4.8 nm diameter retaining a small orientation distribution of 4.1°.

Effect of inhomogeneous microstructure of granular layer on inter granular/inter layer exchange coupling in stacked perpendicular recording media

The effect of inhomogeneous microstructure of granular layer on inter granular/inter layer exchange coupling in stacked perpendicular recording media is studied by varying SiO2 content of CoCrPt-SiO2 granular layer. From cross-section and plane-view TEM observation, it can be concluded that each magnetic grain at cap layer (CL) grows on one magnetic grain of granular layer (GL), and inhomogeneous nucleation site at GL leads to inhomogeneous initial growth of continuous layer at CL. This phenomenon leads to the increase of inter granular coupling fluctuation in CL. Evaluation of inter granular coupling between magnetic grains at GL in stacked media with CL deposited directly on GL shows average and fluctuation of exchange coupling constant of around 2.9 erg/cm2 and 0.6 erg/cm2. In order to reduce the inter granular coupling, spacer layer (SL) with Pd material was inserted between GL and CL. As a result, average and fluctuation of exchange coupling constant decrease to 1.4 erg/cm2 and 0.3 erg/cm2 which sugg...

Evaluation of interlayer ferromagnetic coupling for stacked media by adding reference layer

The trial for quantitative evaluation of interlayer ferromagnetic coupling between granular and cap layer in stacked media is reported. The evaluation is realized by analyzing M-H loop of stacked media with another reference layer added on the cap layer. The reference layer is antiferromagnetically coupled with the cap layer through non-magnetic spacer layer. In this experiment, Rh which leads to antiferromagnetic coupling constant along film normal direction of around 2 erg/cm2 was used as non-magnetic spacer layer. According to the evaluation result done by this method, when thickness of the spacer Pd layer between granular layer and cap layer is increased to 1.1 nm, ferromagnetic coupling constant is weakened to 7.2 erg/cm2 which results in reduction of saturation field.