Magnetic measurements on vacuum-annealed orthorhombic ${\mathrm{Pb}}_2$${\mathrm{Sr}}_2$${\mathrm{PrCu}}_3$${\mathrm{O}}_{8+\mathit{y}}$ (y≊0) reveal an anomalous Pr antiferromagnetic ordering at ${\mathit{T}}_{\mathit{N}}$(Pr)≃6 K with transition onset up to 11 K. This Pr-2213 compound shares common structural features with the tetragonal Pr-123 compound ${\mathrm{PrBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_6$, which also undergoes a Pr ordering at 10 K. However, oxygenated pseudotetragonal ${\mathrm{Pb}}_2$${\mathrm{Sr}}_2$${\mathrm{PrCu}}_3$${\mathrm{O}}_{8+\mathit{y}}$ (y≊1) exhibits only low transition onset around 3 K, while orthorhombic ${\mathrm{PrBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ has a higher ${\mathit{T}}_{\mathit{N}}$(Pr) value of 17 K. Complementary studies by adiabatic calorimetry on ${\mathrm{Pb}}_2$${\mathrm{Sr}}_2$${\mathrm{PrCu}}_3$${\mathrm{O}}_8$ yield a specific-heat anomaly with a peak near the magnetically derived ${\mathit{T}}_{\mathit{N}}$(Pr), with onset around 11 K. A large heavy-fermion-like linear term in the specific heat prevails as often observed in other Pr-containing high-${\mathit{T}}_{\mathit{c}}$ systems. The magnetic entropy Δ${\mathit{S}}_{\mathit{m}}$ below 11 K onset is relatively small, only 13% of R ln3 for ${\mathrm{Pr}}^{3+}$ with a quasitriplet ground state, implying a quasi-2D nature of the magnetic ordering with a strong 2D short-range magnetic correlation which persists to higher temperatures in this extremely anisotropic structure.

• Received 14 April 1994

DOI:https://doi.org/10.1103/PhysRevB.50.3288