Revisiting of Specific Heat of Nonsuperconducting PrBCO Ceramics in Orthorhombic Phase: Signature of Magnetic Phase Transitions at Low Temperatures

The magnetic and electronic contributions of the Pr ions only to the specific heat C
_p
(T) and entropy S(T) defined by ΔC
_p
(T) and ΔS(T), respectively, are revisited at low temperatures for nonsuperconducting PrBa
₂
Cu
₃
O
_6+x
ceramics with x = 1 and 0.95. Two small anomalies are observed below the well-known anomaly due to the antiferromagnetic (AFM) ordering of the Pr sublattice at the Néel temperature T
_N
= 17.5 and 14 K, respectively. The first one, which occurs near the transition temperature T
₂
~ 10.5 and ~9.5 K, respectively, is due to the effect of the previous spin reorientation phase transition of the Pr moments. Whereas the second one, which appears for both states at the same critical temperature T
_cr
~ 4-5 K, is caused by the noncollinear magnetic reordering of the Pr subsystem. A phenomenological analysis is used in the fitting procedure below T
_cr
. The values of the associated electronic linear coefficient Δγ are found for both states fairly lower than those deduced from previous measurements on ceramics and single crystals in orthorhombic phase. In addition to the common T
³
contribution to ΔC
_p
(T), which characterizes the Pr AFM ordering, the T
⁵
contribution associated with the rather significant Pr-Cu(2) magnetic coupling introduces some nonlinear magnetic effects. All results are discussed and compared with earlier reports.