Hirofumi Kondo

Structural characteristics and magnetic properties of chemically synthesized CoPt nanoparticles

CoxPt100−x nanoparticles with dimensions from approximately 2 to 5 nm were synthesized using the reverse micelle method. High-resolution electron microscopy revealed single- and poly-crystalline nanoparticle structures. Twin boundary is a common feature in the polycrystals. As-grown nanoparticles did not show any coercivity at room temperature. However, the nanoparticles became ferromagnetic after annealing at 550 °C for 4 h. Face-centered-cubic to face-centered-tetragonal phase transformation of the nanoparticles that occurred at annealing temperatures above 550 °C was confirmed by electron diffraction patterns and x-ray diffractometry. Coercivity of the annealed nanoparticles were found depending on the nanoparticle chemical compositions. Composition atomic ratio of Co to Pt at around unity gives the highest coercivity of 5500 Oe at room temperature.

Fabrication of monodispersive FePt nanoparticle films stabilized on rigid substrates

Monodispersive FePt nanoparticle films can be stabilized firmly on rigid Si substrates using amino-functional silane, such as [3-(2-aminoethlyamino) propyl]trimethoxysilane, as a coupling layer. The Si substrate/SiO2/APTS/FePt nanoparticles heterostructure was confirmed using high-resolution electron microscopy (HREM). The HREM result agreed well with the x-ray reflectivity measurement upon the individual layer thickness. The as-made superparamagnetic FePt nanoparticle film transformed from chemically disordered fcc structure to chemically ordered L10 phase upon annealing at 800 °C for 30 min under a vacuum of 10−8 Torr. Plan-view high-resolution scanning electron microscopy (HRSEM) observation indicated that under high-vacuum annealing, coalescence of the monodispersive nanoparticle film was not significant. The HRSEM result was consistent with the in-plane x-ray diffractometry measurement, in which sharpening of the diffraction peaks occurred only very slightly for the annealed films.

Atomic composition effect on the ordering of solution-phase synthesized FePt nanoparticle films

FePt nanoparticle monolayer films were fabricated with the nanoparticles stabilized on organic-coupling-layer coated Si substrates. The as-prepared films were nonmagnetic. In order to transform the nanoparticle phase from chemically disordered face-centered-cubic to chemically ordered L10, the films were annealed at 800°C under nitrogen atmosphere for 30min. The annealed films showed different degrees of sintering depending on the organic coupling layer materials used. At room temperature, sintered films exhibited high coercivity up to 2.4×104Oe, while monodispersive films with insignificant sintering showed a low coercivity of 1.1×102Oe. Such results can be explained by a large atomic composition distribution among the nanoparticles together with the size effect on ordering. Improvement of the nanoparticle atomic composition homogeneity is essential for applying the nanoparticle films for future ultrahigh-density data storage applications.

Frictional properties of novel lubricants for magnetic thin film media

In order to achieve the required contact-start-stop (CSS) durability in a rigid-disk system, the authors investigated the relationship between CSS durability and lubricant structure in terms of polar group. The strong adhesion of the lubricant onto the disk surface gives rise to a large adsorption heat and shows the ability to withstand numerous CSS operations. CSS durability is also ascribed to the conformal film formation of the lubricant, which is prepared by the spontaneous adsorption method on the disk surface. Based on these findings, the authors designed and synthesized lubricants which exhibit improved performance compared to conventional perfluoropolyethers. >

Lubrication of modified perfluoropolyether on magnetic media

Abstract The effect of the polar group of perfluoropolyether (PFPE) on the friction of metal evaporated (ME) tape is presented in this paper. The newly synthesized amine salt has a better frictional characteristic than other conventional polar groups in 100 reciprocating motions and even shows a coefficient of 0.21, which becomes over 0.3 for the PFPE, and the difference is enhanced with surface smoothness. Stick-slip motion was not observed even for the smooth surface for the modified PFPE tape. The relation between the surface energy and friction is complicated, but the amine salt being tightly anchored to the rubbing surface covers uniformly which leads to better lubricity. Moreover, the modified PFPE are dissolved in alcohol and hexane, which makes practical use convenient without any environmental problems.

Comparison of an Amide and Amine Salt as Friction Modifiers for a Magnetic Thin Film Medium

The frictional properties of a novel lubricant on a thin film magnetic medium are presented. The novel carboxylic amine salt has better frictional characteristics than the corresponding amide. The microscopic coverage of the lubricant film on the magnetic medium also is investigated by means of FTIR. Coverage does not change during reciprocating motion for the amine salt, which tightly anchors to the surface, since the friction coefficient is low and steady. The friction coefficient of the amine salt decreases with increasing lubricant on the surfaces. In contrast for the amide, the rubbing contact process breaks the lubricant film and results in high friction coefficient, since the amide has weak interaction with the surfaces. The friction coefficient is almost independent of the amount of the lubricant for the amide.

Behaviour of lubricant migration in particulate magnetic recording media

The effect of the recovery speed of lubricant on the durability of particulate magnetic media is presented in this paper. The use of newly synthesized perfluoropolyethers (PEPEs) in particulate media allows us to evaluate the amount of surface lubricant and the migration by X-ray photoelectron spectroscopy (XPS). The migration rate of the lubricant is evaluated as the change of the XPS peak area after argon etching to remove the surface lubricant. A recovery speed depends on the kind of lubricant and way of coating. Furthermore, lubricant of higher recovery speed has better stability of friction coefficient.

Effect of double bonds on friction in the boundary lubrication of magnetic thin film media

Abstract The effect of double bonds in a lubricant on the friction of metal evaporated (ME) tape is presented. New carboxylic acid stearyl amine salt derivatives were used as lubricants. The double bond incorporated in the hydrophobic group of the lubricant raises the friction of the ME tape. Not only the number but the position of the double bond influences the friction. The friction coefficient of the unsaturated hydrocarbon becomes enormously higher with the number of test cycles. On the other hand, the friction coefficient of a saturated hydrocarbon acid is low and steady. The terminal double bond effect is an increase in friction compared with that of a central position. The lubricant film on the surface was also investigated by means of Fourier transform infrared spectroscopy. The thickness of the paraffinic lubricant did not change after 100 cycles. In contrast, the olefinic lubricant thickness decreases with the rubbing process, which leads to an increase in friction, since the double bond interacts with the counterpart and migrates to it.

Tribochemical Reactions on the Surfaces of Thin Film Magnetic Media

An experimental study has been performed regarding the effect of extreme pressure (EP) additives on minimizing friction in order to achieve the required frictional properties of thin film magnetic media. In shuttling motion, disulfide additives had no effect on friction, due to their inability to form a protective film. While alkyl phosphite changed the surface to phosphate film and reduced the coefficient of friction, aryl phosphite was less effective because of the steric hindrance of the aromatic ring generated by hydrolysis. Together with the results of the enthalpy of preferential adsorption measurements, it was concluded that the effectiveness of alkyl phosphite as an EP additive depended on the formation of a protective film on the rubbing surface and on the strength with which the lubricant anchored to the outermost phosphate surface. Based on these findings, a combination of alkyl phosphite and the ester lubricant exhibited further improved performance for magnetic thin film media.

Novel Ionic Lubricants for Magnetic Thin Film Media

New protic ionic liquids (PILs) have been developed. The kinetic friction coefficients of ammonium salts of the alcolate, the carboxylate, and the sulfonate were from 0.23, 0.17, and 0.15, respectively, and 0.26 for Fomblin Z-DOL. PILs have better friction and wear properties compared to Z-DOL. The ammonium salts as a hydrophilic group have a lower frictional coefficient, which enhanced the abrasion resistance. The friction and the thermal degradation decreases with the increasing between the Broensted acid and the Broensted amine. The material based on an ammonium sulfonate has higher , and does not decompose even at 300 , making it more thermally stable than Z-DOL.