Anomalous Hump Research Articles

Magnetic Properties of New Cubic-Perovskite Mixtures; (La0.5Na0.5)RuO3 and (Ca1-xAx)RuO3 (A=Mg, Sr)

To clarify the nature of the ferromagnetic interactions in SrRuO 3 , the Ru 4+ – –Ru 4+ exchange couplings in cubic-perovskite type ARu 4+ O 3 (A=nonmagnetic cation.) were investigated. Magnetic measurements were done on these sample oxides (including single crystals of CaRuO 3 ) by using a magnetic balance technique. In contrast to the ferromagnetic behaviors in (Ca 1- x Sr x )RuO 3 ( x ≧0.4), both the (La 0.5 Na 0.5 )RuO 3 metallic and (Ca 1- x Mg x )RuO 3 ( x =0.1, 0.3 and 0.5.) semiconductive systems were found to be Curie-Weiss paramagnets having negative asymptotic Curie points. On the (Ca 0.8 Sr 0.8 )RuO 3 sample, an anomalous hump of χ vs T curve was observed, which could be interpreted as being due to ferromagnetic clusters of Sr 2+ . It was suggested that, besides the 180° superexchange coupling, another indirect-exchange interaction via Sr 2+ would be indispensable for the ferromagnetism in SrRuO 3 .

Electrical Properties of Stannous Selenide

The electrical resistivity, Hall coefficient and thermoelectric power were investigated over the temperature range from 100° K to 800° K on pure and impurity-doped SnSe crystals. An anomalous hump of the Hall coefficient was found to occur at about 200°C in most of the as-grown crystals and this seems to make the conventional analysis based on a simple semiconductor model impossible. Anisotropies in the resistivity and Hall coefficient were also studied on single crystals and the observed anisotropy in the resistivity seems to be ascribed to an anisotropy in the effective mass of holes. Hole mobility varies as T -2.0 at high temperatures and its discrepancy from T -1.5 law is explained on the assumption of both optical and acoustical mode scatterings. Further investigation was made of the anomalous Hall coefficient on heating the specimen at various temperatures in vacuum. This anomalous phenomenon was found to depend on the heat-treatment history of the crystal and the experimental results were analysed on such a simple model that acceptors are introduced into SnSe by impurity diffusion above 200°C and caused to disappear on heating at lower temperatures. General features observed seem to be in fair agreement with the proposed model.