Anomalous magnetic phase diagram in low-carrier two-band systems and possible application to CeOs4Sb12

摘要

Magnetic properties under the external field are investigated in low-carriertwo-band systems, which may explain the nontrivial phase boundary found intemperature vs. magnetic field diagram discovered in some materials, such asfilled-skutterudite compound CeOs$_{4}$Sb$_{12}$. Analysis is made both for theperiodic Anderson model with the small-dispersive $f$ band and the simplifiedtwo parabolic band model in the vicinity of the Fermi level. The magneticsusceptibilities are calculated by using the random phase approximation. It isshown that the maximum value of the magnetic susceptibility perpendicular tothe external field is enhanced and yields the anomalous phase boundary. Byapplying the magnetic field, the phase boundary shifts to higher temperatureregion in the insulating state with a small band gap. On the other hand, thesimilar phase boundary also appears in the semi-metallic states, in which thestructure of the density of states in the vicinity of the Fermi level and thefinite temperature effect are essential.