ABSTRACT
Low-temperature and elastic properties of the quasicrystal approximant GdCd6have been investigated by means of an ultrasonic measurement. Salient elastic anomalies were observed in the temperature and magnetic field dependence of the principal elastic constants, most probably being associated with the successive multiple magnetic phase transitions showing up at low temperatures. Based on the experimental data, a magnetic field vs temperature phase diagram was constructed. In a zero magnetic field, at least four phases appear to exist. However, the phase diagram both for the magnetic field applied forH//⟨100⟩andH//⟨110⟩is richer, and interestingly some phase boundaries correspond to the development of field-induced phases, leading to the intricate magnetic phase diagram possibly with multiple ordered phases. We discuss the elastic and electronic properties at low temperatures, and also the nature of the multiple magnetic phase transitions of GdCd6.
ABSTRACT
We report the anisotropic changes in the electronic structure of a Kondo semiconductor CeOs(2)Al(10) across an anomalous antiferromagnetic ordering temperature (T(0)) of 29 K, using optical conductivity spectra. The spectra along the a and c axes indicate that an energy gap due to the hybridization between conduction bands and nearly local 4f states, namely the c-f hybridization gap, emerges from a higher temperature continuously across T(0). Along the b axis, on the other hand, another energy gap with a peak at 20 meV becomes visible at 39 K (>T(0)) and fully opens at T(0) because of a charge instability. This result implies that the appearance of the energy gap, as well as the change in the electronic structure along the b axis, induces the antiferromagnetic ordering below T(0).
