Narrow-gap semimagnetic semiconductors

Abstract

We demonstrate, both experimentally and theoretically, subwavelength waveguiding and imaging through a one-dimensional (1D) array of 3D metallic H-fractals. The waveguide formed by the fractal array is subwavelength in all cross-sectional dimensions, thereby allowing compact designs for guided propagation of long-wavelength EM waves. The underlying physics is governed by the fractal metallic wire structure that allows subwavelength resonances. The measured results indicate that such waveguides can provide low-loss propagation of EM waves with a decay length in the range 10-40 m, achieved through coupling of resonant dipoles/multipoles between neighboring H-fractals along the wave propagation direction. By treating the waveguide as a 1D photonic crystal, the calculated bandstructure shows that in the neighborhood of peak transmission frequencies the dispersion relations are relatively flat as a function of the wave vector, implying low group velocities. This is experimentally verified.Owing to the increased spatial information carried at such transmission frequencies, imaging becomes possible and this was observed by placing an obstacle at the inlet and scanning the local field intensity at the other end of the waveguide.

Spintronics and spintronics materials

“…Spin glasses also exhibit a giant Zeeman splitting and can be used for fabri cation of ferromagnetic-normal semiconductor contacts and other hybrid systems possessing ferromagnetic and semiconducting properties. [240][241][242] Strong exchange interactions in the doped type II-VI paramagnetic materials also favor high spin polarization of carriers in external magnetic fields. Indeed, though a strong exchange interaction between the Mn 3d states and the semiconductor states causes no ferromagnetic ordering of the Mn moments, an external magnetic field polarizes the manganese spins; the intrinsic magnetic field of the Mn spins causes a giant spin splitting.…”

The Shubnikov–de Haas Effect in Semiconductors: A Comprehensive Review of Experimental Aspects

“…These optical SdH experiments are analogous to the dc SdH effect with the optical or highfrequency conductivity being enhanced by the passage of a Landau level through the Fermi level of a degenerate semiconductor. In addition, there have often been reviews of specific semiconductors in which the SdH work on them has been presented and discussed [e.g., the Hgi^Cd^Te alloy system by Dornhaus and Nimtz (1983); the narrow-gap lead salts by Nimtz and Schlict (1983); narrow-gap semimagnetic semiconductors by Lyapilin and Tsidil'kovskii (1985)]. The reader should be aware that all these effects exist, but we choose not to emphasize them here.…”

“…Thus, at relatively high temperatures one can apply Adams and Holstein's formula to interpret SdH data, and extract fundamental band parameters like E g and P. At low temperatures, a modified Pidgeon-Brown model incorporating the s-d exchange interaction is used to calculate the Landau-level energies. Additional SdH studies on Hgi^Mn^Se were carried out by Lyapilin et al (1983 and Gavaleshko et al (1984). The Landau-level energies were then compared with the observed SdH peak positions as shown in fig.…”

“…A new term (Bastard et al 1977) in the Pidgeon-Brown Hamiltonian (Pidgeon and Brown 1966) is introduced and accounts for many features of the SdH data. Lyapilin et al (1983) state that the procedure used by Takeyama and Galazka (1979) and Byszewski et al (1980) to determine values for the exchange parameters is unsatisfactory and gave some reasons for their objections. 10, allowing values for the two exchange parameters α and β to be determined.…”

Synthesis, structure, and magnetic properties of anion-substituted manganese chalcogenides

“…In particular, the Néel tem perature increases and reaches T N = 520 K at the pres sure P = 8 GPa, while the energy gap in the spectrum of electronic excitations decreases by a factor of 2. A decrease in the length of the metal-anion Mn-Te bond, according to theoretical calculations of the electronic band structure [9], induces a change in the crystal structure from hexagonal (H) to cubic (ZB) with the antiferromagnetic type of ordering. For the antiferromagnetic type of ordering, the difference between the binding energies per Mn-Te pair is ΔE ZB, H = (-0.21) + (-0.…”