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Register a new userAnomalous low temperature state of CeOs4Sb12: Magnetic field and La-impurity study
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Specific heat for single crystalline samples of Ce1-xLaxOs4Sb12 at zero-field and magnetic fields to 14 T is reported. Our results confirm enhanced value of the electronic specific heat coefficient in the paramagnetic state. They provide arguments for the intrinsic origin of the 1.1 K anomaly. This transition leads to opening of the gap at the Fermi surface. This low temperature state of CeOs4Sb12 is extremely sensitive to chemical impurities. 2% of La substituted for Ce suppresses the transition and reduces the electronic specific heat coefficient. The magnetic field response of the specific heat is also anomalous.
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Magnetic properties under the external field are investigated in low-carrier two-band systems, which may explain the nontrivial phase boundary found in temperature vs. magnetic field diagram discovered in some materials, such as filled-skutterudite compound CeOs$_{4}$Sb$_{12}$. Analysis is made both for the periodic Anderson model with the small-dispersive $f$ band and the simplified two parabolic band model in the vicinity of the Fermi level. The magnetic susceptibilities are calculated by using the random phase approximation. It is shown that the maximum value of the magnetic susceptibility perpendicular to the external field is enhanced and yields the anomalous phase boundary. By applying the magnetic field, the phase boundary shifts to higher temperature region in the insulating state with a small band gap. On the other hand, the similar phase boundary also appears in the semi-metallic states, in which the structure of the density of states in the vicinity of the Fermi level and the finite temperature effect are essential.
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