1202.1724 (Julian G. Sereni)

Thermodynamic analysis of the Quantum Critical behavior of Ce-lattice
compounds    [PDF]

Julian G. Sereni

A systematic analysis of low temperature magnetic phase diagrams of Ce
compounds is performed in order to recognize the thermodynamic conditions to be
fulfilled by those systems to reach a quantum critical regime and,
alternatively, to identify other kinds of low temperature behaviors. Based on
specific heat ($C_m$) and entropy ($S_m$) results, three different types of
phase diagrams are recognized: i) with the entropy involved into the ordered
phase ($S_{MO}$) decreasing proportionally to the ordering temperature
($T_{MO}$), ii) those showing a transference of degrees of freedom from the
ordered phase to a non-magnetic component, with their $C_m(T_{MO})$ jump
($\Delta C_m$) vanishing at finite temperature, and iii) those ending in a
critical point at finite temperature because their $\Delta C_m$ do not decrease
with $T_{MO}$ producing an entropy accumulation at low temperature.
Only those systems belonging to the first case, i.e. with $S_{MO}\to 0$ as
$T_{MO}\to 0$, can be regarded as candidates for quantum critical behavior.
Their magnetic phase boundaries deviate from the classical negative curvature
below $T\approx 2.5$\,K, denouncing frequent misleading extrapolations down to
T=0. Different characteristic concentrations are recognized and analyzed for
Ce-ligand alloyed systems. Particularly, a pre-critical region is identified,
where the nature of the magnetic transition undergoes significant
modifications, with its $\partial C_m/\partial T$ discontinuity strongly
affected by magnetic field and showing an increasing remnant entropy at $T\to
0$. Physical constraints arising from the third law at $T\to 0$ are discussed
and recognized from experimental results.

View original: http://arxiv.org/abs/1202.1724