Specific heat analysis of the low temperature anomalies in orthorhombic PrBa₂Cu₃O_6+x (x = 1; x = 0.95) compounds

The specific heat C_p(T) and entropy S(T) properties of the orthorhombic PrBa₂Cu₃O_6+x compounds in two states of oxygen concentration x, an over doped (OV) with x = 1 and an optimally doped (OP) with x = 0.95 are reanalyzed below the Néel temperature of the antiferromagnetic ordering of the Pr sublattice T_N = 17.5 and 14 K, respectively. Two simultaneous anomalies for both states are observed. The first one occurs near the previous spin reorientation phase transition temperature T₂ ∼ 11.5 and ∼ 9-10 K, respectively whereas the second one remains close to the so called low-critical temperature T_cr ∼ 4-5 K for the OV state as it has been reported before for the OP state. By fitting the C_p(T)/T data to A{T²}^-3/2 + γ + C{T²}¹ + D{T¹}² for T < T_cr the four coefficients obtained with the best adjusted A-squared values are compared with previous findings. Reduced values for y are confirmed in this work. The results which are well described by the contribution of the DT⁵ term to C_p(T) can be connected with the previous Pr-Cu(2) magnetic coupling that is sufficiently enough to cause a modest spin reorientation phase transition at T₂ and a critical magnetic behaviour below T_cr.