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 PrBa2Cu3O6.95 (PrBCO6.95) 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 Neel temperature of the antiferromagnetic ordering of the Pr3+ sublattice T-N = 14 K. Using Arrott plot analysis, we identified weak field-induced phase transitions at two critical fields, H-cr1(T) similar to 3.3 T and H-cr2(T) similar to 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 chi(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.