Anomalous kondo effect and ordered state in heavy fermion system SmOs ₄Sb₁₂: Resistivity, Sb-NQR, and magnetization measurements under high pressure

We report resistivity, nuclear quadrupole resonance (NQR), and magnetization measurements under high pressures in a novel heavy fermion compounds SmOs₄Sb₁₂. The resistivity and nuclear spin-lattice relaxation rate 1/T1 show the coherent behavior below a characteristic temperature T* = 20 25 K at ambient pressure. Nuclear spin-spin relaxation rate 1/T₂ was found to show a peak of electrical origin around T*. Some charge fluctuation is considered to play an important role in the Kondo effect of SmOs₄Sb₁₂. On the other hand, the magnetization at low temperature does not increase under pressures, although the transition temperature increases. The NQR signals are strongly suppressed around the transition temperature and vanishes at low temperatures. These suggest that the ordered state in SmOs₄Sb ₁₂ is not simple ferromagnetism.