Carrier States and Ferromagnetism in Diluted Magnetic Semiconductors

Applying the dynamical coherent potential approximation to a simple model, we have systematically studied the carrier states in $A_{1-x}$Mn$_xB$-type diluted magnetic semiconductors (DMS's). The model calculation was performed for three typical cases of DMS's: The cases with strong and moderate exchange interactions in the absence of nonmagnetic potentials, and the case with strong attractive nonmagnetic potentials in addition to moderate exchange interaction. When the exchange interaction is sufficiently strong, magnetic impurity bands split from the host band. Carriers in the magnetic impurity band mainly stay at magnetic sites, and coupling between the carrier spin and the localized spin is very strong. The hopping of the carriers among the magnetic sites causes ferromagnetism through a {\it double-exchange (DE)-like} mechanism. We have investigated the condition for the DE-like mechanism to operate in DMS's. The result reveals that the nonmagnetic attractive potential at the magnetic site assists the formation of the magnetic impurity band and makes the DE-like mechanism operative by substantially enhancing the effect of the exchange interaction. Using conventional parameters we have studied the carrier states in Ga$_{1-x}$Mn$_x$As. The result shows that the ferromagnetism is caused through the DE-like mechanism by the carriers in the bandtail originating from the impurity states.Comment: 20 pages, 14 figure

Influence of lamination orientation and stacking on magnetic characteristics of grain-oriented silicon steel laminations

Analytical and experimental investigations have been carried out upon the behaviour of flux in laminations, where the rolling directions of adjacent sheets are reversed. The paper clarifies the mechanism of the greatly different magnetic characteristics between such laminations and usual ones, where the rolling directions of adjacent sheets are coincident.</p

Characteristics of cosmic ray pole-equator anisotropy derived from spherical harmonic analysis of neutron monitor data

The spherical harmonic analysis of cosmic ray neutron data from the worldwide network neutron monitor stations during the years, 1966 to 1969 was carried out. The second zonal harmonic component obtained from the analysis corresponds to the Pole-Equator anisotropy of the cosmic ray neutron intensity. Such an anisotropy makes a semiannual variation. In addition to this, it is shown that the Pole-Equator anisotropy makes a variation depending on the interplanetary magnetic field (IMF) sector polarities around the passages of the IMF sector boundary. A mechanism to interpret these results is also discussed

3-D FEM analysis of the effects of SPT head dimensions on recording in discrete and continuous media

Due to the considerable increase of magnetic recording density, the deviation of the head from the centerline of the track becomes a serious problem for the cross-track interference. In this paper, a three-dimensional read/write simulation system was used to investigate the effect of the width of the write head on the behavior of the flux and magnetization for continuous track medium and discrete track medium. It is shown that the magnetization in a neighboring track of the discrete track medium is smaller than that of the continuous track medium. The output of the read head using the discrete track medium is larger than that of the continuous track medium when a suitable read head width is chosen so that the cross talk is negligible.</p

Investigation of effectiveness of various methods with different unknown variables for 3-D eddy current analysis

Computer codes using the A-&#966;, A-&#966;-&#937;, A*-0&#937;-E, T-&#937;, and E-&#937; methods were developed. The effects of the volume ratio of the conductor region to the whole region, the shape of the conductor, and the ratio of the hole region to the conductor region on the computer storage, the CPU time, and the accuracy of the methods are investigated systematically using a few simple models. The effect of the conductivity of the conductor is also examined. The computer storage, the CPU time, and the error are found to increase with increase of the volume ratio of the conductor region to the whole region. The computer storage and the CPU time are affected by the shape of the conductor in some methods of analysis. The error of the A*-&#937;(E-&#937;) method is larger than that of the other methods</p

New technique for producing a strong multi-pole magnet

A new technique for producing strong multipole magnet is developed. A cylindrical magnet oriented with its easy axis of magnetization perpendicular to the cylinder axis is magnetized by a multipole magnetizer. This procedure results in a multipole magnet with a flux density almost sixty percent greater than the flux density produced by a multi-pole magnet which is not oriented. The technique is especially effective for producing small cylindrical magnets with many poles and agreement of a theoretical analysis with experimental results is very good, with deviations of no more than a few percent.</p