T. Onoue

Analysis of microstructures for Co/Pd multilayer perpendicular magnetic recording media with carbon underlayer

Abstract The effect of amorphous carbon underlayer thickness on the microstructure of the Co/Pd multilayer perpendicular magnetic recording media was investigated. From the magnetic force microscopy observation in the AC-demagnetized state of the Co/Pd multilayer media, the magnetic cluster size was observed to effectively decrease with an increase in carbon underlayer thickness, where the higher coercivity and the higher S / N ratio of the Co/Pd multilayer media were obtained with the thicker underlayer. Furthermore, the distribution of [1xa01xa01] orientation of FCC-Pd became broader, and the grain size decreased with an increase in the carbon underlayer thickness. These effects caused the magnetic exchange decoupling of Co/Pd multilayer media. We suggested that the change of microstructure was directly related to the surface roughness of the amorphous carbon underlayer.

Effect of underlayers on magnetic properties of Co/Pd multilayer perpendicular magnetic recording media

Abstract Amorphous C and Si films were sputter-deposited as underlayers of Co/Pd multilayer perpendicular magnetic recording media. The magnetic properties of the media were significantly affected by the underlayer thickness; namely, the values of coercivity H c and nucleation field − H n increased and the value of α decreased with merely increasing the thickness of C or Si underlayer, where α is the derivative of M – H loop at the value of coercivity. The coercivity was not always affected by magnetic anisotropy constant K u for the Co/Pd media. In read–write experiments, the higher S/N ratio was obtained for the media with the thicker C or Si underlayer, which exhibited low α and high H c . In the time decay experiments of magnetization, the Co/Pd multilayer media with C or Si underlayer possessed good thermal stability. This study demonstrated that the introduction of C or Si underlayer greatly improves magnetic properties, read–write characteristics, and thermal stability of Co/Pd multilayer perpendicular magnetic recording media.

Enhancement of magnetic properties of Co/Pd multilayered perpendicular magnetic recording media by using Pd/Si dual seedlayer

Abstract Effects of the introduction of a Pd/Si dual seedlayer on the microcrystalline structure and magnetic properties of [Co/Pd] n multilayered perpendicular magnetic recording media were investigated. The Pd/Si dual seedlayer was composed of a Pd upper seedlayer and a Si under seedlayer. The Pd upper seedlayer with a thickness of up to 10xa0nm markedly increased the coercivity of [Co/Pd] n multilayered media in the direction perpendicular to the film surface. The highest coercivity of 7.8xa0kOe was obtained for the [Co/Pd] 10 medium with a Pd (10xa0nm)/Si (100xa0nm) dual seedlayer. The Pd upper seedlayer not only facilitated the formation of regular interfaces between the Co and Pd layers, but also reduced the thickness of the deteriorated initial layer in the [Co/Pd] n multilayer, resulting in enhancement of the magnetic anisotropy field. The [Co/Pd] n multilayered medium with the Pd/Si dual seedlayer exhibited weak intergranular exchange coupling between [Co/Pd] n grains, which led to excellent read–write characteristics.

Microstructure and magnetic properties of Co/Pd multilayered thin films with C or Si seedlayer

Microstructure and magnetic properties of sputter deposited Co/Pd multilayered perpendicular magnetization films with amorphous C or Si seedlayer were investigated. The angstrom scale surface roughness of the seedlayer causes fine crystal grains to form in the Co/Pd multilayer and to decrease the extent of intergranular exchange coupling, while it obstructs the formation of a regular interface between Co and Pd layers. The Si seedlayer, which exhibits a surface roughness lower than the C seedlayer, yields Co/Pd multilayered films with the lowest intergranular exchange coupling and the highest coercivity. The improvement in magnetic properties of the Co/Pd film with Si seedlayer is attributable mainly to the formation of Pd2Si at the interface between the Co/Pd layer and the Si seedlayer. The Pd2Si provides suitable nucleation sites for the grain growth of Co/Pd multilayered film that can be utilized as a perpendicular magnetic recording medium.

CoCrPtTa single layer perpendicular magnetic recording media with carbon underlayer

Sputter-deposited amorphous carbon was applied as an underlayer for a Co73Cr18Pt6Ta3 single layer perpendicular magnetic recording medium. It is shown that the amorphous carbon underlayer can control the Co [001] preferred orientation of the Co73Cr18Pt6Ta3 magnetic recording layer and that the microcrystalline structure, magnetic properties, and read–write characteristics of Co73Cr18Pt6Ta3 media are greatly dependent on the carbon underlayer thickness. By x-ray diffraction experiments and transmission electron microscopy observations, it was confirmed that the distribution of the c-axis orientation of Co grains becomes broader in the direction perpendicular to the film surface with increasing carbon underlayer thickness. Furthermore, the Co73Cr18Pt6Ta3 medium with a thick carbon underlayer indicated a relatively high perpendicular coercivity of 2800 Oe and an excellent signal to noise ratio in read–write characteristics.

CoCrPtTa and Co/Pd perpendicular magnetic recording media with amorphous underlayers

The effect of amorphous carbon underlayers on magnetic properties and read-write characteristics of Co/sub 73/Cr/sub 18/Pt/sub 6/Ta/sub 3/ single layer and Co/Pd multilayer perpendicular magnetic recording media were investigated. The increase in H/sub c/ and decrease in /spl alpha/, defined as 4/spl pi/(dM/dH)/sub H=Hc/, were observed by increasing the underlayer thickness for both Co/sub 73/Cr/sub 18/Pt/sub 6/Ta/sub 3/ and Co/Pd media. The media with a low /spl alpha/ value, suggesting a decrease in the exchange coupling, exhibited the higher coercivity and the improvement of S/N ratio. In read-write experiments, the improvement of S/N ratio for the Co/Pd media was achieved up to 400 kFRPI or even higher in the recording density by increasing carbon underlayer thickness, while that for the Co/sub 73/Cr/sub 18/Pt/sub 6/Ta/sub 3/ media was obtained up to ca. 250 kFRPI.

Relationship between surface energy and preferred orientation of CoCr alloy magnetic thin films deposited on C and TiCr underlayers

The relationship between crystallographic grain orientation and the three kinds of surface energy components; dispersion, polar, and hydrogen bonding components, in Co 73 Cr 18 Pt 6 Ta 3 perpendicular magnetic recording media with an amorphous C or a Ti 90 Cr 10 underlayer was discussed. Each surface energy component of the thin film was calculated from an extended Fowkes theory by measuring the contact angle of a test liquid on the thin film. The experimental results revealed that the polar component of surface energy of the Co 73 Cr 18 Pt 6 Ta 3 magnetization film with the C underlayer affected greatly the Co [001] preferred orientation of the Co 73 Cr 18 Pt 6 Ta 3 magnetization film, while the surface energy of the Co 73 Cr 18 Pt 6 Ta 3 magnetic layer with the Ti 90 Cr 10 underlayer had little influence on the distribution of it.

The effect of external magnetic field on mark size in heat-assisted probe recording on CoNi/Pt multilayers

A method of heat-assisted magnetic recording potentially suitable for probe-based storage systems is characterized. In this work, field-emission current from a scanning tunneling microscope tip isused as the heating source. Pulse voltages of 2-7 V were applied to a CoNi/Pt multilayered film. During heating, various external magnetic fields were applied. Experimental results show that apositive magnetic field increases mark size while a negative field decreases mark size, compared to the case of writing without an external field in which an average mark size of 170 nm was achieved.In addition, a positive field reduces the threshold voltage of writing as well. A synthesized model is built to quantitatively simulate the experimental results. It includes the model of emission current,heat transfer, and dynamics of magnetic domains in the film. Simulation results show that the calculated mark size in various cases is consistent with experimental results. Based on this model,we will be able to figure out the proposals to achieve small marks for the goal of 1 Tbit/ in.2 recording density.

Influence of substrates on magnetic property and crystalline orientation of CoCrTa/TiCr perpendicular magnetic recording medium

The influence of substrates on magnetic property and crystalline orientation of CoCrTa/TiCr perpendicular magnetic recording medium was investigated using a glass plate and a Si(1 0 0) single crystal. Magnetic measurements revealed that the film sputtered on a Si(1 0 0) substrate possessed a higher perpendicular coercive force than that on glass, where the pretreatment of the Si(1 0 0) substrate by aqueous HF solution effectively improved the magnetic properties. X-ray diffraction analysis of the films indicated that the crystallinity of the TiCr layer formed on the Si(1 0 0) substrate with the HF pretreatment was higher than that on the glass substrate. It was also found that CoCrTa and TiCr layers on the Si(1 0 0) substrate with the HF pretreatment had a narrower distribution of their c-axis orientation than those on glass substrate. The results of X-ray diffraction analysis were consistent with those of the TEM observation for cross-section bright- and dark-field images and the corresponding THEED patterns. These results suggest that the crystalline surface of the Si(1 0 0) substrate with HF pretreatment has the effect of inducing preferred orientation in the TiCr underlayer, which leads to a decrease in distribution of the c-axis orientation of Co grains in the CoCrTa layer, resulting in an increase in the perpendicular coercive force.