Synthesis and anomalous magnetic properties of CoCr2O4 nanocrystallites with lattice distortion

Nanocrystalline Cobalt chromite (CoCr2O4) ceramic has been synthesized under a mild condition, rather than by a high-temperature sintering (e.g. >1673 K, in general). A shifted hysteresis loop with an exchange-bias field of 35.7 kA/m and a high coercivity of 627.9 kA/m at 4.2 K was achieved under the cooling field of 2.39×106 A/m. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) results reveal that a strong lattice distortion and a large amount of surface defects exist in CoCr2O4 nanocrystallites (NCs). The anomalous magnetic properties, such as bias field and large coercivity, are attributed not only to the nanosize effect but also to the lattice distortion and crystal defects.