Y. Inaba

Optimization of the SiO/sub 2/ content in CoPtCr-SiO/sub 2/ perpendicular recording media for high-density recording

Optimization of the SiO/sub 2/ content for high-density recording was discussed for {(Co/sub 90/Cr/sub 10/)/sub 80/Pt/sub 20/}/sub 100-Z/-{SiO/sub 2/}/sub Z/ perpendicular recording media. The grain size D/sub grain/ decreases significantly from 8.8 to 5.4 nm as the SiO/sub 2/ content Z increases from 0 to 14.4; however, no significant difference in c-axis orientation was observed. Magnetocrystalline anisotropy of grains maintains a large value of nearly 8/spl times/10/sup 6/ erg/cm/sup 3/, even at 10 at % SiO/sub 2/ addition, indicating a high potential of perpendicular anisotropy K/sub u/ to resist thermal agitation of magnetization. The coercivity H/sub c/ increases significantly as the SiO/sub 2/ increases, which is coincident with the reduction of the slope of magnetization curve /spl alpha/=4/spl pi/(dM/dH) due to the enhancement of grain isolation. The H/sub c/ shows a maximum at around 11 at % SiO/sub 2/ (nearly 30 vol % SiO/sub 2/). A further increase of SiO/sub 2/ reduces the value of H/sub c/ significantly, although the /spl alpha/ maintains a constant value of nearly 2, due to thermal agitation of magnetization. The media noise reduces significantly as the SiO/sub 2/ increases; however, the addition of SiO/sub 2/ beyond about 13 at % leads to a slight increases in media noise probably due to a significant increase of thermal agitation. The recording resolution D/sub 50/ shows a broad maximum of /spl sim/420 kFCI at around 11 at % SiO/sub 2/, suggesting that the D/sub 50/ is related to the media noise performance. Experimental results indicate that there is a tradeoff to be made between the thermal stability and media noise performance as a function of SiO/sub 2/ composition.

Ku2 magnetic anisotropy term of CoPtCr-SiO2 media for high density recording

Measurements of higher energy term of magnetic anisotropy, Ku2, in CoPtCr–SiO2 perpendicular recording media are described. It was revealed that the values of Ku2 and the first order energy term, Ku1, vary significantly according to the seed layer material used, however, no significant change in the ratio of Ku2∕Ku1 was observed on the addition of SiO2 to CoPtCr films. Ku2 increases and Ku1 decreases as the c∕a ratio of the hcp-CoPtCr lattice increases. It is concluded that CoPtCr films have sufficient potential in the values of Ku1 and Ku2 for high density perpendicular media.

Dot arrays of L10-type FePt ordered alloy perpendicular films fabricated using low-temperature sputter film deposition

Using ultrahigh vacuum sputter film deposition, we fabricated L10-type Fe50Pt50 ordered alloy perpendicular films on MgO(001) single-crystal substrates and 2.5 in. glass disks at low substrate temperatures of 200–350u2005°C. Then we examined the magnetic properties of the dot arrays made from these films. The uniaxial magnetic anisotropy Ku for L10-type FePt films (10 nm in thickness) deposited with a Pd underlayer on MgO(001) substrates reached about 2u2009×u2009107 erg/cm3 at the substrate temperature Ts of 200u2005°C, and 3u2009×u2009107 erg/cm3 at Tsu2009=u2009250u2005°C. The order parameter S was about 0.46 at Tsu2009=u2009300u2005°C. Moreover, Ku for L10-FePt films fabricated on glass disks using MgO/Cr underlayers shows 3.4u2009×u2009107 erg/cm3 at Tsu2009=u2009300u2005°C, which was almost equal to that for FePt single-crystal films deposited on Pd/MgO(001). The switching field distribution σ/Hc for dot arrays made from L10-FePt film [5 nm in thickness, on Pd/MgO(001) at Tsu2009=u2009250u2005°C] was small; σ/Hc = 0.11 for a dot diameter of 15 nm. This value was smaller than th...

Magnetic cluster size and activation volume in perpendicular recording media

The magnetic cluster size Dcluster of perpendicular recording media, which is a main factor in media noise, is discussed in terms of activation volume, intergranular exchange coupling, and the slope of magnetization curves. It was experimentally shown that the values of Dcluster (observed by magnetic force microscopy in the ac demagnetized state) are ∼55 nm for CoPtCr–SiO2 media of 24 nm thickness, and are several times larger than activation diameter Dact (Dact=Vact/δ, Vact; the activation volume). Dcluster decreases as the film thickness δ decreases, particularly in a series of media with small intergranular exchange coupling, while Dact is nearly constant at ∼10 nm. It was experimentally shown that the slope of the magnetization curve α decreases as the value of Dcluster/δ decreases, and reaches a value of approximately 1 at Dcluster/δ of around 2. The results suggest that reduction of film thickness δ is important in order to realize both small Dcluster and large α values in granular-type perpendicula...

Thermal stability and recording writability of hard/soft stacked perpendicular media

Magnetic properties and recording performance were studied for hard/soft stacked media consisting of a magnetically hard CoPtCr–SiO2 layer (10nm thickness) underneath a soft granular layer. Various kinds of soft layers [NiFe(Cr)–SiO2,CoCr–SiO2,…] were used in the present study. Transmission electron microscope images revealed that the grains of the soft layer grew on CoPtCr grains in all kinds of stacked media with SiO2 segregated at the grain boundaries. However, it was revealed that the grain isolation becomes degraded at the film surface when the soft layer was thicker than a critical thickness, and this thickness was about 7nm for (NiFe∕CoPtCr)–SiO2 media. The stacked structure reduced the coercivity, with no significant change in the slope of the magnetization curve. The reduction in dynamic coercivity H0 reached about 2kOe for stacked media with 3nm soft layers, allowing a reduction of the saturation recording current. Furthermore, no significant changes in the signal to media noise ratio SNmR and t...

Characterization of coercivity at a recording speed of granular media for thermally assisted recording

As a fundamental study of thermally assisted recording, remanence coercivity at recording speed and the energy barrier for magnetization switching for granular media were evaluated as a function of temperature T. We characterized those for CoPtCr-oxide granular media as a trial examination. Remanence coercivity was measured at measurement time t′ of 1 s (using an electromagnet) and 10−5 s (pulse field); they were defined, respectively, as Hr and HrP for T of 300–473 K. Assuming that the value of t′ at a recording speed is 1 ns and the value of remanence coercivity at the recording speed, Hr(1 ns), was evaluated by fitting Hr and HrP to Sharrock’s equation. Moreover, the values of the energy barrier for magnetization switching, ΔE, were estimated. The value of Hr(1 ns) at Tu2009=u2009573 K, which is a typical temperature for thermally assisted recording, as estimated by extrapolation was about 6.2 kOe for the single medium and 5.5 kOe for the stacked medium. These values were about 1 order of magnitude larger than...

CoPtCr-SiO/sub 2/ perpendicular media with the high order energy term of magnetic anisotropy for high density recording

The fabrication of CoPtCr-SiO/sub 2/ perpendicular recording media was studied having adequate values of uniaxial magnetic anisotropy values, K/sub u1/ and K/sub u2/. It was concluded that there is a high possibility of fabricating K/sub u2/ media for high density recording, although more intensive effort is required to confirm advantages by K/sub u2/ term.