The puzzling properties of the first order phase transition in YbInCu4 and its alloys in the wide range of magnetic fields and temperatures are perfectly described in terms of a simple entropy transition for free Yb ions. In particular, it turns out that the transition line in the (B,T)-plane is very close to the elliptic shape, as it has been observed experimentally. Similar calculations are done, and the experiments are proposed for the (γ−α) phase transition in Ce in Megagauss fields. We speculate, that in case of YbInCu4 the first order transition is a Mott transition between a higher temperature phase in which localized moments are stabilized by the entropy terms in the free energy, and a band-like non-magnetic ground state of the f-electrons.
@article{arxiv.cond-mat/0008134,
title = {First order valence transition in YbInCu_4 in the (B,T) - plane},
author = {M. O. Dzero and L. P. Gor'kov and A. K. Zvezdin},
journal= {arXiv preprint arXiv:cond-mat/0008134},
year = {2009}
}