Synthesis and size dependent exchange bias effect in CoCr2O4/Cr2O3 nanogranular systems

Abstract

Structure and magnetic properties have been investigated on the nanogranular systems of ferrimagnetic (Ferri) CoCr2O4 nanoparticles embedded in antiferromagnetic (AFM) Cr2O3 matrix, synthesized by a phase segregation route from diluted Cr2(1−x)Co2xO3 (x=0.1) oxides. The CoCr2O4 nanoparticles with average particle size (DCCO) from 8 to 60nm can be produced by varying synthesis temperatures. Magnetization measurement show that, both exchange bias fields (HEB) and vertical magnetization shift (MShift) can be found at 10K after field-cooled from 350K. With increasing particle size (DCCO), both HEB and MShift decrease monotonically and finally disappear as particle size is above 60nm. The linear relationship between HEB and MShift indicates that the interfacial frozen uncompensated spins play a critical role in inducing exchange bias effect.