Satoru Momose

Disk substrate deposition techniques for monodisperse chemically synthesized FePt nanoparticle media

Self-assembled FePt nanoparticles hold promise for future ultrahigh-density magnetic recording media because of their high anisotropy and capability to be formed into small and uniform grains. By using a special spin coater, we were able to form a dense array of FePt particles across the entire surface of a 2.5 in. disk substrate. Our method can control the number of layers of FePt nanoparticles. The media deposited with FePt nanoparticles by the spin coater was annealed in a vacuum. We measured read–write properties of the FePt nanoparticle media on a spin stand, and succeeded in detecting a signal of 290 kfci.

Fine Tuning of the Sizes of FePt Nanoparticles

Fine tuning of the sizes of FePt nanoparticles has been realized by a simple modification of a solution phase synthesis, which consists of the decomposition of Fe(CO)5 and the reduction of Pt(acac)2. The key method used to control the particle size is the use of surfactants, and only a change in their amount is required to vary the average sizes of the FePt nanoparticles from 2 to above 4 nm. The resultant nanoparticle volume is proportional to the surfactant amount; this makes the synthesis of FePt nanoparticles of desired sizes possible.

Magnetic properties of magnetically isolated L10-FePt nanoparticles

This letter reports the results obtained by measuring the temperature dependence of the coercivity of magnetically isolated L10-FePt nanoparticles in agglomeration-free films deposited by using a dispersion stabilizer and a spin-coat technique. These measurements not only give the basic magnetic parameters of the nanoparticles but also provide information about the nanoparticle ordering process. The temperature at which isolated FePt nanoparticles start to order seems to be about 650°C.

L10-FePt nanoparticles in a magnetically isolated state

A novel technique for fabricating a L10-FePt nanoparticle film in a magnetically isolated state is reported. An organic mixture, which stabilizes colloids, inhibits the nanoparticles from forming agglomerations during annealing at up to 800°C, and the resulting film shows the included FePt nanoparticles to be L10 phase and magnetically isolated. Such a film indicates a steep decline in coercivity with the temperature increase whereas the nanoparticles have a large uniaxial anisotropy energy density because of thermal relaxation that corresponds to the particle size.

Integration of organic photovoltaic and thermoelectric hybrid module for energy harvesting applications

A new energy harvesting hybrid device that operates selectively in photovoltaic (PV) mode or thermoelectric (TE) mode has been proposed, and successfully fabricated using organic materials. Here, while keeping the TE properties comparable to the best data ever reported, PV properties have been improved dramatically, and the electrical properties of PV/TE hybrid cells with organic materials are reported for the first time. Also, organic hybrid modules on flexible films were fabricated, and this new technology would pave the way for new energy harvesting applications.

Hard Magnetic FePt Nanoparticles by Adsorption-Annealing and Orientation Control

Chemically synthesized FePt nanoparticles are attractive material for magnetic recording media, because of the small size and narrow size distribution. Here we report the fabrication of hard magnetic fct-FePt nanoparticles from chemically synthesized superparamagnetic FePt nanoparticles by annealing following their adsorption onto a zeolite surface. This process enabled the preparation of colloidal fct-FePt nanoparticles with average size of 5.1 nm and size distribution of 8%, respectively. The thus obtained fct-FePt nanoparticles can be oriented using baking in a magnetic field; the resultant coercivities at 300 K are 3.09 kOe and 9.86 kOe in the parallel and perpendicular directions respectively.

Magnetic orientation of chemically partially ordered FePt nanoparticles by annealing in magnetic field

We have investigated a method of magnetically orienting FePt nanoparticles. Uniaxial magnetic crystals such as chemically ordered FePt can be oriented by an external magnetic field. We therefore attempted to prepare colloidal chemically ordered FePt nanoparticles, using a surface reduction and heat treatment. The heat treatment changed the crystal structure of the nanoparticles from disordered to partially ordered, sustaining the colloidal status. A film of the partially ordered nanoparticles was then annealed in a magnetic field. As a result, the annealed film became magnetically anisotropic; that is, both coercivity and magnetic squareness along the direction of the applied field during annealing were >30% larger than those along the perpendicular direction. Although the observed magnetic anisotropy differed from the ideal, we analyzed the resultant magnetic orientation status by applying switching field distributions (SFDs). The analysis implied that annealing in a magnetic field has great potential for orienting uniaxial magnetic nanoparticles.

Highly selective and sensitive gas sensors for exhaled breath analysis using CuBr thin film

We have examined a p-type semi-conductor CuBr thin film used for sensor devices that indicates the order of sensitivity to ammonia in parts per billion (ppb). The CuBr thin film also indicates excellent selectivity to ammonia among reductive gases, which additionally suggests its capacity for fast quantification of the order of seconds. Moreover, CuBr thin film can be adapted to a high-sensitivity aldehyde sensor by a surface modification. Since the fabrication process of CuBr thin film is compatible with an ordinal CMOS process, there is a potential for development into highly integrated and low power consumption sensor devices. These properties make CuBr thin film a promising candidate as a gas sensing material for human-breath analysis.

Magnetic properties of a real FePt nanoparticle system

In this paper, we report a chemically ordered and agglomeration-free FePt nanoparticles system, which is enabled by adding an agglomeration inhibitor. The inhibitor is so effective that gives agglomeration-free status after post-anneal under vacuum, even if it is carried out at 800/spl deg/C. This method therefore revealed magnetic properties of FePt as isolated nanoparticles.