Bibliothek

Notizen: A small dc brushless spindle motor with small magnetic flux leakage must be used for a CD-ROM drive application because the magnetic flux leakage may affect the magnetic and electric control circuit of the pickup head. This paper presents a motor design that efficiently reduces magnetic flux leakage by using a pair of yokes on the rotor magnet. Using these yokes at a distance of 2.0 mm reduced the magnetic flux leakage from 344 to 29 G along the radial direction and from 117 to 10 G along the axial direction. After shielding for the magnetic flux leakage, the dynamic performance of the motor cannot be affected. The torque of the CD-ROM spindle motor can be controlled at the same range for shielded and unshielded spindle motors. © 1996 American Institute of Physics.

Notizen: Recently, new mechanisms have been proposed to explain the giant enhancements of M-O Kerr effect. In this work, we use magnetic image effect to explain the Kerr angle enhancement of M-O media on Co-base amorphous films. The M-O layer and reflection layer were produced by using conventional dc magnetron sputtering processes. The Kerr hysteresis loops of M-O films were measured with wavelength from 500 to 860 nm, and the peak applied field was 9 kOe. We have studied the enhancements of Kerr angle in TbFeCo amorphous film which sandwiched by AlN layers and backed with Co-base amorphous film. There is a remarkable increase of Kerr angle with value 1.85° at wavelength 640 nm. At wavelength 780 nm, the Kerr angle of magneto-optic medium on Co-base amorphous ribbon has been significantly enhanced by a factor of 3.1 as compared to that on Al foil. Because of its high permeability and low coercivity, the Co-base amorphous film serve as a magnetic shielding material which can induce the magnetic image effect for M-O film. Theoretical calculations show that the Kerr angle can be enhanced by the image magnetic field. The calculated values of Kerr angle are in good agreement with experiment results. An explicit equation to calculate the Kerr angle will be discussed. © 1996 American Institute of Physics.

Notizen: The effects of Zn ion on magnetic properties Fe3O4 magnetic colloids were investigated in this study. Fe3O4 magnetic colloids were produced by the chemical coprecipitation method, i.e., mixing an acidic solution containing FeCl2⋅4H2O, FeCl3⋅6H2O, ZnCl2⋅4H2O, with a NaOH alkali solution at 70 °C, and then centrifuging them from the mixed solution. Various reaction times, solution pH values, and Zn ion contents were also used. Fe3O4 magnetic fluid was obtained by adding ammonium oleate into the mixed solution, precipitating the colloids from the solution, neutralizing the colloids by hydrochloric acid, and dispersing the colloids in n-hexane. XRD, EDX, TEM, and VSM were used to determine the structure, chemical compositions, particle sizes, and magnetic properties of the colloids and the magnetic fluid. The spinel colloids was easily form at a higher pH value in solutions where the pH value ranged from 7 to 12. Fe3O4 colloids were completely formed within the first minute of mixing and the particle size of Fe3O4 colloids did not increase with time after the first minute.The lattice parameter of Fe3O4 colloids increased linearly with the Zn ion content because the diameter of Zn ion is larger than that of Fe ions. The particle size of Fe3O4 colloids was found to be 10 nm by TEM. For an initially fixed Zn content of 8 wt % in solutions, the Zn content in the Fe3O4 colloids ranged from 3.32 wt % at pH=5 to a maximum value of 7.85 wt % at pH=10. Later, it reduced to 7.51 wt % at pH=12 because Zn ion has the lowest solubility at pH=10. At 8 wt % of zinc ion in the solution, the σs of the Fe3O4 colloid increase sharply from 0 at pH=3 to 92 emu/g at pH=8 and then reach a maximum value of 94 at pH=10. The σs value and Hc value of the Fe3O4 colloid were found significantly improved by adding a suitable amount of Zn ions, e.g., ranging from 70 emu/g and 48 Oe at Zn=0 wt % to a maximum 94 emu/g and 50 Oe at Zn=7.14 wt %. Later they reduced to 70 emu/g and 44 Oe at Zn=12.52 wt % when prepared at pH=10. The σs value of the magnetic fluid was found linearly proportional to the colloid content in the magnetic fluid. For a colloid containing 7.51 wt % of Zn ion, the σs value of the magnetic fluid is 9.8 emu/g at 25 wt % of colloid. © 1996 American Institute of Physics.