Initial susceptibility investigation of magnetic transitions in several rare earth metals: Thermal hysteresis in ferromagnetic transitions

Abstract

In general, it is very difficult to define a “band gap” in organic materials. The ultra-violet spectrum of the solid is almost identical to that of the molecules in the vapor phase. Therefore, light absorption is essentially determined by the single molecules. Thus, no relation between thermal and optical band gap is to be expected or found.Phenomenologically, anthracene can be used for an illustration of most of the properties encountered. Surface currents and bulk currents have been observed and separated experimentally. Under inhomogeneous illumination, space charge effects, the Dember effect, and many other related phenomena have been detected. The photoresponse is closely related to the absorption spectrum and depends critically on the geometrical arrangement. The material is exceedingly sensitive to neutron irradiation. The high impedance of the material precludes measurements of the Hall or photo-electromagnetic effect, but recently the hole and electron mobilities have been measured by a pulsed photoconductivity technique. It was found that the mobilities are of the order of 1 cm2/V-sec and anisotropic. A theoretical calculation of this anisotropy has been successful.The magnitude of the photocurrents and their spectral sensitivity can be changed markedly by absorption of electron acceptors, or donors, on the surface of the crystals. This leads to the conclusion, already inferred from other work, that most of the charge carriers are generated in the surface layer.