Magneto-optical polarization rotation was studied in materials magnetized in an arbitrary orientation with respect to the light beam propagation direction. The Jones matrix of these media was derived, as was a theoretical expression representing the polarization rotation for the linear polarization incident with an arbitrary azimuth. This theoretical expression was confirmed through an experimental study by using a magnetic colloid which shows a large linear birefringence along with a magnetic circular birefringence. The expression shows that, when the linear birefringence and dichroism are not small enough in relation to the circular birefringence, the polarization rotation is obviously not proportional to the magnetization component parallel to the light beam. Even when the linear birefringence and dichroism are small, the proportionality decreases as the light beam path becomes longer. For the incident linear polarization of the axis parallel or perpendicular to the plane defined by the magnetization and the light beam, this problem is less remarkable.
Fe70Co30 single-layer films with various thicknesses were deposited on glass substrates by RF sputtering. We investigated the dependence of magnetic properties and film structure on the film thickness. Fe-Co films with thicknesses of less than 50 nm show isotropic magnetic properties. Increasing the Fe-Co film thickness brings about uniaxial magnetic anisotropy and low coercive force. Frequency dependence of initial permeability for the 770-nm-thick Fe-Co film is markedly different from the theoretical one, because of magnetic anisotropy dispersion. With an increase in the Fe-Co film thickness, the crystal orientation changes and the I(211)/I(110) intensity ratio becomes stronger. These structural features may be related to the appearance of uniaxial magnetic anisotropy and low coercive force.
This paper describes an experimental study of the conduction noise of a micro dc-dc converter during high-speed CMOS-logic IC loading. For comparison, experimental results obtained by using a commercialized on-board dc-dc converter are also shown. When the dc-dc converter is used as the power supply of the CMOS logic circuit, the converter noise is modulated by the clock signal of the CMOS-IC, and transmitted to the logic circuit by amplitude modulation. Since the output noise of the micro dc-dc converter module is very small, the effect of amplitude modulation by the clock signal of the CMOS-IC is relatively small. The low noise level is due to the small leakage flux of the inductor with a closed magnetic circuit, and small parasitic inductance in the converter circuit.
This paper reports the effects of the thermal fluctuation aftereffect and the eddy current on the measurement of hysteresis curves for high-coercivity Nd-Fe-B sintered magnets. Hysteresis curves were measured with a vibrating sample magnetometer using a superconducting magnet (SCM-VSM) and a pulsed field magnetometer (PFM) over a long period in the same maximum field of 4 MA/m. Spherical specimens with a diameter of 6.0 mm were used, and the demagnetization field was compensated for by using a demagnetizing factor N=1/3. In this experiment, the anisotropy field value obtained from the intersection of the magnetization curves of an M-type Sr ferrite magnet sintered at 1240°C was used for common magnetic field normalization. In the case of the SCM-VSM method, where the waiting time varied from 2 to 20 s, the difference in the HcJ value was small. However, the difference in Hk was 40-90 kA/m. In a comparison of the SCM-VSM and PFM methods, the values of HcJ and Hk in the PFM method showed increases of 30 and 90-190 kA/m, respectively. The eddy current influence strongly affected the measured value of Hk in the case of the PFM method. Hysteresis curves swelled under the influence of the eddy current.
A rotating machine with a stator slot has an energy loss caused by pulsation of the magnetic flux density distribution in the air-gap part. This loss is called the tooth pulsation loss. The purpose of this paper is to discuss the mechanism of a decrease in the tooth pulsation loss achieved by the use of ferrite magnetic wedges. We chose a capacitor motor as an object of analysis. We propose a method for estimating the tooth pulsation loss from the induced voltage of a virtual coil placed on the rotor surface. By analyzing the induced voltage of a virtual coil, using harmonic analysis, we clarified the relation of the tooth pulsation loss to the number of stator slots and the magnetic characteristics of the wedge materials.