Griffiths phase, spin-phonon coupling, and exchange bias effect in double perovskite Pr2CoMnO6

Abstract

The ceramic Pr2CoMnO6 of double perovskite structure is prepared by a solid-state reaction and the magnetic properties, phonon behaviors are studied in detail. Two ferromagnetic transitions at TC1 ∼ 172 K and TC2 ∼ 140 K are observed in the temperature-dependent magnetization curves, respectively. Furthermore, a detail analysis on the magnetic susceptibility reveals that a short-range ferromagnetic clustered state exists above TC1, which can be well described as the Griffiths phase with a well-defined Griffiths temperature TG ∼ 210 K. The presence of the B-site antisite defects is considered to contribute to the observed Griffiths singularity. Temperature-dependent Raman scattering experiment reveals an obvious softening of the phonon mode involving stretching vibrations of the (Co/Mn)O6 octahedra in FM temperature regions, indicating a close correlation between magnetism and lattice in Pr2CoMnO6. On the other hand, it is found that the phonon softening extends up to TG, which further confirms the preformation of the short-range ferromagnetic clusters up to TG. Moreover, the field-cooling magnetic hysteresis loop reveals that exchange bias phenomena is present, which is supposed to origin from the exchange coupling between Co/Mn ordered ferromagnetic phases with antiferromagnetic antiphase boundaries caused by the partially Co/Mn antisite disorders. These findings give a systematic understanding on the magnetic interaction in Pr2CoMnO6 which is closely related to the lattice and atomic distribution, and add special interest for application of this material.