Papers by Keyword: Magnetic Semiconductors

Abstract: Optical and magneto-optical properties of GaMnSb layers fabricated on GaAs (001) substrates by laser ablation technique were studied using spectral ellipsometry (E =1.24-3.25 eV) and the transversal Kerr effect (TKE) (E = 0.5 4.2 eV) as well as atomic and magnetic force microscopy. Spectra of the constituents of the diagonal components of the permittivity tensor as well as TKE depended substantially on the layer fabrication conditions. At room temperature a strong resonant band was observed in the TKE spectra for the GaMnSb layers with low Mn content in the energy range E 0.5-1.5 eV. This resonant TKE band was explained by excitation of surface plasmons in MnSb nanoclusters, which arose during the growth of the layers. In the energy region E >1.5 eV the TKE spectra were related to interband transitions in MnSb inclusions.

Abstract: Polycrystalline stoichiometric Co-substituted ZnO oxides have been synthesized by solid state reaction via sintering ZnO and Co powders in air. The precise nature of magnetic coupling is determined by studying carefully structural and magnetic properties. The magnetization as a function of temperature for Zn1-xCoxO (x = 0.02, 0.05, 0.0625 and 0.10) can be fitted well to a model with a paramagnetic Curie term, an antiferromagnetic Curie-Weiss term and a diamagnetic constant, which could arise from spins of isolated Co ions, grouped Co ions that are in nearest neighbor positions and a diamagnetic background, respectively. The substitution of Co at the Zn sites does not occur in a completely random manner but the Co ions appear to have a tendency for grouping. It is interesting to note in Raman measurements that host lattice defects with 2 distinct impurity modes may be induced by isolated and grouped Co spins.

Abstract: It is shown that in colossal magnetoresistance materials an inhomogeneous alternating magnetic field generates a strong electric field of non-inductive nature. This magnetoelectric effect is an analog of acoustoelectric effect in conventional semiconductors. Due to the above electric field spin waves in the former materials, like acoustic waves in the latter ones, acquire an additional attenuation at equilibrium. This attenuation may be converted to amplification by applying strong enough dc electric field drifting the carriers (solid-state Cherenkov’s effect). The experiments, which probed this phenomenon in HgCr2Se4 using spin wave pumping, are discussed.