CoPt Grains Research Articles

Micromagnetic study of CoPt–SiO2 granular films by spin-wave Brillouin scattering

A spin-wave Brillouin scattering study of a CoPt–SiO2 granular magnetic recording medium was made. This film contains ferromagnetic CoPt particles in a SiO2 matrix, and has an extremely low medium noise property due to little exchange coupling between magnetic grains. Spin waves of both the propagating surface mode and standing wave mode were found to be excited in granular magnetic films with various microstructures. A possible origin of the spin wave is a magnetostatic coupling between regularly ordered CoPt grains, as reported for artificially patterned magnetic thin films. This result shows two promising features of the CoPt–SiO2 granular film for high density recording medium: It is an ordered media obtained in a self-organizing manner, and it is less influenced by the thermal fluctuation effect, which is a serious problem for current high density magnetic recording.

Self assembled nanoparticulate Co:Pt for data storage applications

Nanoscale CoPt grains were prepared within protein shells from aqueous reactants. A series of particles with varying Co:Pt ratios was used to explore the transition from superparamagnetic to ferromagnetic behavior at room temperature. TEM and electron diffraction confirmed ordered fct CoPt phases with an average grain size of 4.1 nm. Magnetic characterization was performed at room temperature using VSM. The use of this system to prepare high-density recording media is discussed.

Surface etching effect of Co/sub 80/Pt/sub 20/-SiO/sub 2/ granular media

We have fabricated Co-Pt alloy-SiO/sub 2//Cr granular media and etched by RF biasing the magnetic layer surface to reduce the effect of isolation and finer Co-Pt grains. The magnetization decreased slightly with film thickness reduction. The in-plane coercivity H/sub c/ was maintained down to a magnetic layer thickness of 11 nm. Meanwhile, the perpendicular H/sub c/ decreased with reduced film thickness. This indicates that the magnetization easy axes orientations of the grains in the etched layer were 3D-random and that epitaxial growth occurs on the Cr under layer. Signal at high linear densities was increased with film etching presumably due to the good easy axes orientation of the remaining layer. The signal to media noise ratio was improved by 1 dB but the thermal stability of magnetization was slightly lessened.

High-density recording capability of granular media composed of Co-Pt grains and SiO/sub 2/ matrix

Co-Pt and SiO/sub 2/ granular films were prepared on a Cr seed layer. Co-Pt grains dispersed in the SiO/sub 2/ matrix discretely. Conical grains grew in contact with the Cr layer and spherical grains grew between the conical ones. Coercivity exceeded 2 kOe and coercive squareness reached about 0.7 at a remanent magnetic moment of 0.4 memu/cm/sup 2/. Activating magnetic moment was 10/sup -15/ emu and the index of the thermal stability was about 100. Bit error rate was held below 10/sup -5/ up to a linear density of 280 kfci. The recording pattern at the track width of 1 /spl mu/m was clearly visible. The Co-Pt and SiO/sub 2/ granular media have potential for 5 Gb/in/sup 2/ recording.

Effects of Pt addition on the magnetic and microstructural properties of CoC granular films

The magnetic properties and microstructures of granular Co/sub 60-X/Pt/sub X/C/sub 40/ (0/spl les/x/spl les/23) thin films, fabricated by ion-beam sputtering and subsequent annealing, were investigated. High coercivity was obtained in samples with Pt concentrations ranging from 12 to 16 atomic percent, with a maximum coercivity of 1800 oersteds. These films consisted of CoPt grains having a CoPt disordered alloy phase, which were separated by a C phase. The magnetic grains had an average size of 10 nm and a faulted hexagonal close-packed structure. Below 16 at.% Pt content, the improvement in coercivity with Pt was most likely related to an increase in the magnetocrystalline anisotropy of the CoPt alloy compared to that of the Co. Above 16 at.% Pt content, a drastic decrease in coercivity was observed. It is found that for these large Pt concentrations a higher annealing temperature is required to improve the coercivity with Pt addition.

Magnetic properties and structure of (Co-alloy)-SiO/sub 2/ granular films

We fabricated (Co-alloy)-SiO/sub 2/ granular films by rf-sputtering with composite target and annealing in a high vacuum environment. The coercivity of the films depended on annealing temperature, the Co-alloy's volume fraction in the film, and other added elements to cobalt. We found that a (Co/sub 85/Pt/sub 15/)/sub 83/-(SiO/sub 2/)/sub 17/ granular film (Co/sub 85/Pt/sub 15/: 64 vol.%) exhibited about 1600 Oe of coercivity at room temperature. The grains diameter was about 50 nm measured by AFM. X-ray diffraction patterns showed that the Co-alloy grains of most films had an fcc-phase structure. From Henkel-plot analysis, the magnetic exchange interaction between the CoPt grains was found to be weak.