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A systematic investigation of structure and intrinsic magnetic properties of the novel compounds R3(Fe, T)29 (R=Y, Ce, Nd, Sm, Gd, Tb, and Dy; T=V and Cr) has been performed. The lattice constants and unit cell volume decrease with increasing the rare-earth atomic number from R=Nd to Dy, except for Ce, reflecting the lanthanide contraction. The Curie temperature increases from R=Ce to Gd and decreases from Gd to Dy, respectively, with increasing atomic number and Gd3Fe29−xTx has the highest Curie temperature for each series of R3Fe29−xTx (T=V or Cr) compounds. The saturation magnetization of R3Fe29−xTx at 4.2 K decreases gradually from R=Nd to Dy with increasing atomic number, except for Ce, in each series of R3Fe29−xTx. It is suggested that the Ce ion in Ce3Fe29−xTx is valence fluctuated which leads to the unusual magnetic properties. The spin reorientations of the easy magnetization direction of R3Fe29−xTx are observed at around 230, 230, and 160 K for R=Nd, Sm, and Tb when T=V, and at around 230 and 18...

The intersubband optical absorption and Stark effect of square and step quantum wells in the presence of applied electric field have been investigated theoretically. By considering the tunneling of photoexcited electrons under the influence of electric field in the quantum well, we obtain a shifted and broadened absorption spectrum from the tunneling of electrons. Such broadening leads to a decrease of absorption coefficient when the applied electric field is increased. For detector application of multiple quantum well devices, if efficient tunneling of the photoexcited electrons is desirable for high responsivity, the sharpness of the absorption peak needs to be compromised. Our results provide insight to this broadening and thus the optimization guideline for detector design.

The minimum Reynolds number, ReNc, below which all the two‐dimensional and monochromatic wave disturbances decay, is studied numerically for a thermally stratified plane Poiseuille flow. The ReNc is found to be sensitive to the change of Prandtl number P. Under unstable stratification with Rayleigh number just below critical, ReNc≂1000 is found for P≤10−3.

The phase modulation of asymmetric quantum‐well embedded waveguides is studied. In order to accurately analyze the modulation from quantum wells and optimize the performance of waveguide modulators, a transfer‐matrix method is developed to calculate the bias‐controlled phase modulation of waveguides with an arbitrary refractive index distribution. The refractive index change may include those from free‐carrier effects and the nonlinear effects of bulk material and quantum wells. The linear electro‐optic effect introduced by asymmetric quantum wells can potentially be used to improve the frequency performance of semiconductor waveguide phase modulators.

Capacitance‐voltage measurements of double barrier In0.53Ga0.47As/AlAs resonant tunneling diodes show a large capacitance peak at a bias near resonance. The measured peak capacitance is about five times larger than the calculated depletion capacitance. This large capacitance is interpreted as the capacitance between the emitter and the quantum well, which is activated near resonance only when the quantum well has a sufficient number of electrons to screen the ac electric field. An equivalent circuit with the new added series RC component is proposed and the effect on the high frequency operation of a resonant tunneling diode is discussed.

Outstanding permanent magnet properties were recently observed in a Nd‐Fe‐B compound which was shown to crystallize in a new phase, R2Fe14B. Polarized neutron measurements are reported on Y2Fe14B and Nd2Fe14B single crystals. The 3d Fe moment on different sites in Y2Fe14B at 4.2 K is closely related to local environment. Its value is maximum for atoms in σ‐like layers at the center of an Fe antiprism. On the contrary, it is reduced to 1.95 μB by 4d‐3d electron transfer and hybridization for Fe atoms which have the largest coordinance number of Y atoms, 4. The measurements at 250 K reveal a larger thermal decrease of the 3d moment for Fe atoms which exhibit shortest Fe‐Fe interatomic distances. This property reveals a reduction of 3d magnetic interactions for short distances as was previously observed in R2Fe17 compounds. In Nd2Fe14B, the low values obtained at 4.2 K for Nd magnetic moments suggest that the magnetic structure, determined by a competition between 3d‐4f exchange interactions and crystal‐fiel...