Abstract

The oxygen vacancies (VO) modulating inverse and conventional magnetocaloric effects in double perovskite Bi2NiMnO6-δ polycrystalline films are claimed. The vacuum annealing processor showed large regulated artificial VO concentration from 5.1% to 17.6%, which has been verified by X-photoelectron spectrum results. The role of VO concentration in magnetocaloric effect is clarified by the charge transfer mechanism. The band length and angle (O-Ni-O, O-Mn-O) are sensitive to the valence confusion of elements (Mn and Ni), which is disturbed by VO concentration. This scenario contributes to the spin orientation and antiferromagnetic/ferromagnetic (AFM/FM) competition near the phase transition point by coulomb exchange interaction. The temperature dependent transport behavior, meanwhile, presents metallic-FM state in Bi2NiMnO6-δ (high VO concentration). While stoichiometric Bi2NiMnO6 (low VO concentration) films show dielectric traits. The structure, magnetization and optical absorption properties were characterized systematically. The present work explores a route to design magnetocaloric materials via controllable artificial VO defects.

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