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

• We study the exchange bias effect of the CoCr2O4/Cr2O3 nanogranular systems.
• The exchange bias effect shows strongly particle size dependences.
• Both exchange bias field and magnetization shift is observed in these systems.

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 60 nm 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 10 K after field-cooled from 350 K. With increasing particle size (DCCO), both HEB and MShift decrease monotonically and finally disappear as particle size is above 60 nm. The linear relationship between HEB and MShift indicates that the interfacial frozen uncompensated spins play a critical role in inducing exchange bias effect.