Zero field cooled exchange bias effect in nano-crystalline Mg-ferrite thin film

I report, Zero Field Cooled (ZFC) Exchange Bias (EB) effect in a single phase nanocrystalline Mg-ferrite thin film, deposited on an amorphous quartz substrate using pulsed laser ablation technique. The film showed a high ZFC EB shift (HE~ 190 Oe) at 5 K. The ZFC EB shift decreased with increasing temperature and disappeared at higher temperatures (T > 70 K). This Mg-ferrite thin film also showed Conventional Exchange Bias (CEB) effect, but unlike many CEB systems, the film showed decrease in the coercivity (HC) under the Field Cooled (FC) measurements. The film also showed training effect in ZFC measurements which followed the frozen spin relaxation behaviour. The observed exchange bias could be attributed to the pinning effect of the surface spins of frozen glassy states at the interface of large ferrimagnetic grains.