C.K. Kim

Surface-plasmon resonance of Ag nanoparticles in polyimide

Ag nanoparticles were fabricated by sandwiching a Ag thin film (2.5–15nm thick) between two polyimide precursor layers. During imidization, depending on the initial Ag film thickness, 10–20nm sized Ag nanoparticles arranged in a monolayer were formed within the polymer matrix. The Ag particles exhibited a pronounced localized surface-plasmon resonance effect. The resonance wavelength (460–540nm) can be easily tuned by ±40nm by simply changing the Ag film thickness which alters the mean particle diameter. The classical Mie model was introduced to explain the size dependence of the plasmon peaks.

Structure and magnetic properties of thermally annealed (Ni80Fe20)1−xMnx thin films

Ni80Fe20–Mn alloy thin films were fabricated using magnetron sputtering in order to study the microstructural changes that develop in an exchange couple (Ni80Fe20 and Mn). In the process, we discovered that the alloy films phase separated into Ni80Fe20 and Mn when annealed at 400u200a°C, although bulk Ni80Fe20 and Mn are miscible at room temperature. Moreover, a strong crystallographic texture developed during annealing, especially for films with high Mn content. The increase of texture was attributed to the volume expansion taking place in the phase separation. It was speculated that the as-deposited alloy films had a large coherent interfacial strain, possibly due to inhomogeneous alloying. In turn, this hindered the formation of intermetallic compounds, and instead forced a phase separation to reduce the interfacial energy.

Magnetic Properties and Crystallization of Co - Pt Amorphous Metallic Alloys

Co_(78-x)PtxB_(10)Si₁₂ alloys were produced using the melt-spin process in order to study the crystallization behavior and ensuing magnetic properties of the Co_(78-x)PtxB_(10)Si₁₂ (Co-Pt) amorphous alloys as a function of the Pt content. We showed that when x ＞ 15 well below its stoichiometric composition, CoPt crystallized in the amorphous alloy, thus greatly altering the crystallized microstructure and magnetic properties during annealing. Below this composition, the main crystallization product was Co with Pt dissolved in its lattice. In spite of the nucleation of CoPt with high magnetic anisotropy, the highest coercivity was obtained when x was 15. It was also concluded that the Pt addition deteriorated the glass stability, triggering the devitrification at a progressively lower temperature.

Multi-objective optimal control for EMS based on reduced order observer

In this paper, we develop the design of the multi objective optimal controller for electromagnetic suspension, based on the reduced order observer. First, we derive the static output feedback system with the reduced order observer for EMS systems. The control gain is determined by solving numerically the optimization problem with respect to the multi-objective performance with mixed H₂/H_∞ norm, subject to LMI constraints. The proposed method simultaneously guarantees the stability and H₂/H_∞ norm bounds of the transfer function between exogenous inputs to desired outputs such that the characteristics of single objective methods with H₂ and H_∞ controllers can be considered as performances.

Investigation of Negative Remanence in Cobalt Nanoparticles Fabricated by Laser Irradiation

In this report, we have investigated negative remanence in Co nanoparticles (NP) system by using laser irradiation technique. Magnetization measurements performed on Co NP system show negative remanence taken at temperatures higher than 92 K. The observed negative remanence correlates to the blocking temperature of superparamagnetism. Although we have no clear explanation for negative remanence, this behavior is associated to the magnetic coupling characteristic between the superparamagnetic Co and antiferromagnetic CoO.

Preparation of Ni nanoparticle mono-layer on polyimide substrate

Nanoparticles were produced on polyimide (PI) film through oxidation of a Ni/sub 80/Fe/sub 20/ thin film on a PI precursor layer during its imidization reaction. Film properties were investigated through transmission electron microscopy, electron diffraction and X-ray photoemission spectroscopy. The size and shape of embedded and exposed particles were compared and it was verified that the exposed particles can be effectively used as a growth template for nano-sized structures.

Thermal stability of magnetic tunnel junctions with FeO/sub x/ doped tunnel barrier

Magnetic tunnel junctions were fabricated with tunnel barriers that had a thin film of Fe(0-8 /spl Aring/ thick) inserted in the middle to study the effect of FeO/sub x/ doping on the magneto-electron transport properties of the junction. Tunneling magnetoresistance (TMR) ratio of 24% was realized with the tunnel junction with a 2 /spl Aring/-thick Fe interlayer, whereas the junction without doping did not exhibit the TMR effect. The FeO/sub x/ doping also considerably improved the thermal stability of the junction, retaining the TMR ratio of 15% at 350/spl deg/C.

Magnetic properties of thermally annealed (Ni/sub 80/Fe/sub 20/)/sub 1-x/Mn x thin films

We describe the magnetic properties of thermally annealed (Ni/sub 80/Fe/sub 20/)/sub 1-x/Mn/sub x/ thin films and their inverse magnetoresistance.