Magnetic nature of surface and exchange bias effect in NiO nanosheets

Abstract

The Mesoporous NiO nanosheets with an average thickness of ∼30 nm have been synthesized by annealing Ni(OH)2 precursors. Magnetic measurements show that the NiO nanosheets can be considered as a core-shell type magnetic structure, in which the surface shell layer behaves as a coexistence of two-dimensional diluted antiferromagnetic (2D DAFF) and spin glass (SG) behaviors; the core retains its original bulk antiferromagnetic (AFM) phase. Field-cooled hysteresis loop measurements confirm the presence of exchange bias (EB) effect in the NiO nanosheets. The temperature dependence of the exchange bias field indicates that the observed EB effect originates from an interface exchange coupling interaction between the AFM core and the 2D DAFF shell layer. A phenomenological AFM-DAFF-SG magnetic structure model is proposed to interpret the magnetic properties of these NiO nanosheets.