Exchange bias effect in CuCr2O4/Cr2O3 nanogranular systems

We have successfully synthesized the CuCr2O4/Cr2O3 nanogranular system through a high-temperature phase separation route from Cu doped Cr2O3 nanoparticles, which are confirmed by X-ray diffraction measurements. Magnetic susceptibility shows two magnetic transitions at 130 K and 310 K corresponding to the ferrimagnetic and antiferromagnetic phases of CuCr2O4 and Cr2O3, respectively. Significant exchange bias behavior could be observed in the field cooling magnetic hysteresis loop at low temperatures. Both exchange bias field (HEB) and coercive field (HC) decrease with increasing temperature and disappear near 200 K. This exchange bias behavior is discussed in terms of the existence of exchange coupling between the ferrimagnetic CuCr2O4 and antiferromagnetic Cr2O3. The uncompensated spins in antiferromagnetic phase frozen along field cooling direction provide the pinning force on the ferrimagnetic spins leading to the exchange bias effect.