The magnetic phase transitions in Ce-monopnictides, strong p-f mixing effect

Specific heat of CeBi and CeSb, as well as LaBi and LaSb, was measured from 1.7 to 60 K under magnetic fields of up to 10 T. A Kondo like peak persists in CeBi in whole the studied region. In CeSb the effect of magnetic order is more significant but the similar situation exists, even though crossover from the Γ₇ dominated to Γ₈ dominated Kondo states appears. The γ-value is about 20 mJ/mol K² in both materials with weak field dependence. Phonon softening effect was also observed. It was shown that the extended ANNNI model including non-linear interactions can explain the essential feature of the complicated phase diagram in CeSb fairly satisfactorily.