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We report the structure, magnetic and dielectric properties of CuO nanoparticles synthesized by co-precipitation method. The magnetic measurements reveal the presence of a ferromagnetic (FM) component at room temperature with coercivity of 200 Oe and saturation magnetization of 0.004 emu/g. The observed FM may originate from different valence states of the copper ions due to the oxygen vacancies at the surface/or interface of the particles. In addition, these nanoparticles also exhibit a high dielectric permittivity (\varepsilon^\prime\sim 10^4) with weak temperature dependence in a wide range of temperature. Such a room temperature FM and giant dielectric permittivity without the presence of any transition metal could be a very good option for a class of spintronics. [ABSTRACT FROM AUTHOR]

We report on the magnetic properties of CuO nanoparticles prepared by the sol-gel method. M (T) curves show a blocking temperature at TB = 135 K and 160 K for 13 nm and 17 nm size particles, respectively, in measuring field H = 100 Oe. The M-H data for both the samples show a reversal magnetization at 300 K, whereas below TB it exhibit symmetrical hysteresis loops with a coercive field of 200 Oe (155 Oe) and a remanence 0.306 emu/mole (0.171 emu/mole) for 13 nm (17 nm) at 5 K. Presence of superparamagnetism and net magnetic moments of CuO nanoparticles are attributed to the uncompensated Cu2+ ions at the surface of the particles. [ABSTRACT FROM AUTHOR]

The Fe3O4 powder was mixed with Cu-ferrite powder then sintered in an argon atmosphere at temperatures between 1000 °C and 1250 °C for 4 h. The Cu-ferrite content in the mixture powder was between 0 mol% and 30 mol%. The effects of Cu-ferrite content and sintering temperature on the magnetoresistance (MR) and microstructure of the sintered ferrite were investigated. It was found that the Cu ions were dispersed uniformly in all sinte red samples by the analysis of Cu element mapping of the scanning electron microscopy. The maximum MR ratio of the sintered ferrite at room temperature is about 7.3% when Cu-ferrite content was 7.28 mol% and sintering temperature was 1200 °C. From the plot of log p versus T-1/2 curves and the measurement of the current versus voltage curves of the sintered samples, it can be known that the magnetoresistance mechanisms in these sintered samples are the contribution of spin-polarized tunneling effect. [ABSTRACT FROM AUTHOR]

The slider of a flying pickup head in a near-field optical disk drive has to fly at a stable height above the disk surface. An air bearing force between the slider and optical disk is affected by disk rotation speed and deformation, which represent low-frequency periodic disturbance to the slider. The repetitive control is adopted in this study to eliminate the periodic disturbance. H∞ control inherited with robust properties can deal with model uncertainty and disturbances. Therefore, to solve model uncertainty and disturbance, this study designs a repetitive controller cascaded by an H∞ controller, The proposed controller is validated by experimental results. [ABSTRACT FROM AUTHOR]

Sintered Ni doped Fe3O4 ferrites were prepared by mixing Fe3O4 powder with NiO powder and compressing into pellet, then sintering in argon atmosphere. The contents of Ni in the sintered samples were between 0 at. % and 5.08 at. %. The effects of the. Ni content, sintering temperature and sintering time on the magnetoresistance (MR) and microstructure of sintered Fe3 O4 ferrites were investigated. X-ray diffraction and chemical titration analysis of Fe2+ and Fe3+ ions indicate that the nonstoichiometric phases of Fe3O4 + x and NiFe2 O4- y were co-existed in the Ni doped sample. The optimum sintering temperature, at which the maximum MR value could be obtained, is around 1100 °C and the optimum sintering time is about 9 h for all samples. After sintering at 1100 °C for 9 h, the MR value of the undoped Fe3 O4 ferrite is about 6% at room temperature. Maximum MR value is about 7.5% when 1.12 at.% Ni was doped. It was found that the log p versus T-1/2 curves of all the samples exhibit a linear relationship from the measurement of the electrical resistivity (p) of the sintered samples between 80 K and room temperature. This implies that the MR effect is mainly spin-dependent tunneling where the electrons flow through insulating barriers of Fe2 O3, NiFe3O4 or NiFe2O4-Y. [ABSTRACT FROM AUTHOR]

Studies the possibility of incoherent magnetization reversal process in annealed FeCo/Ag multilayer thin films. Fabrication of the multilayer films; Typical variation of the magnetoresistance (MR) ratio.