  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.
