4f-3d exchange coupling induced exchange bias and field induced Hopkinson peak effects in Gd2CoMnO6

Double perovskite R2CoMnO6 systems, with magnetically active rare earth (R) elements, have attracted much attention because of their interesting field sensitive magnetic phenomena and remarkable physical properties. The perovskite compound Gd2CoMnO6 exhibits a field-induced metamagnetic phase transition from ferrimagnetic to long range ferromagnetic (FM) ordering below a critical temperature of TC ∼112 K. It also shows polarization of the Co/Mn magnetic sublattice to the Gd moments resulting in antiferromagnetic (AFM) like behaviour at TN ∼47 K. Further, the large change in magnetization at low temperatures of T < 10 K originates from the single ion Gd3+ excitations. A sharp peak at TC in AC susceptibility measurements reveals that susceptibility is the sum of the true critical maximum and Hopkinson peak contributions. Below TN ∼47 K, the 4f-3d negative exchange interaction is responsible for the observed antiferromagnetic spin polarizations; consequently the exchange bias (EB) effect originates from the unidirectional anisotropy induced at the antiferromagnetic/ferromagnetic interface.