Magnetic Field-Induced Phase Transition and Weak Ferromagnetism in Nonsuperconducting Optimally Doped PrBCO Cuprate

In this letter, we report anomalous magnetic properties in high dc magnetic fields H up to 11 and 16 T from 1.35 up to 20 K on PrBa ₂ Cu ₃ O _6.95 (PrBCO _6.95 ) cuprate ceramic. Significant magnetic-field effects are revealed in the derivative of the magnetization M ( T ) versus T using two sets of values of H selected in the range of 2.5–9.5 T. Anomalies are observed at the low-critical point T _cr = 4–5 K, in the region of the spin reorientation phase transition temperature T ₂ = 10.5 K, and around the Néel temperature of the antiferromagnetic ordering of the Pr ³⁺ sublattice T _N = 14 K. Using Arrott plot analysis, we identified weak field-induced phase transitions at two critical fields, H _cr1 ( T ) ∼ 3.3 T and H _cr2 ( T ) ∼ 7.5 T, whose associated transition lines exhibit an almost temperature-independent behavior in the range 1.35 K- T ₂ , and seem to vanish in the vicinity of T _N . When T decreases from 20 K, an increase occurs in the derivative of the magnetization M ( H ) versus H for 0.5 T < H < 1 T, as well as in the differential susceptibility χ _d ( T ) versus T where a shape change occurs when crossing T _cr . The spontaneous magnetization M _S ( T ), which was deduced by extrapolation to zero-field from the field-linear regime up to 2 T, shows an inverse variation with T and a shape change when crossing T _N and T ₂ . These features, which are taken as evidence for an additional weak ferromagnetic-like component that survives above T _N , result from the significant role of the Pr-Cu(2) magnetic coupling.