  Exchange bias (EB) phenomena have been observed in Nd2/3Ca1/3MnO3 colossal
magnetoresistance perovskite below the Curie temperature $T_{C}$ = 70 K and
attributed to an antiferromagnetic (AFM) - ferromagnetic (FM) spontaneous phase
segregated state of this compound. Field cooled magnetic hysteresis loops
exhibit shifts toward negative direction of the magnetic field axis. The values
of exchange field $H_{EB}$ and coercivity $H_{C}$ are found to be strongly
dependent of temperature and strength of the cooling magnetic field $H_{cool}$.
These effects are attributed to evolution of the FM phase content and a size of
FM clusters. A contribution to the total magnetization of the system due to the
FM phase has been evaluated. The exchange bias effect decreases with increasing
temperature up to $T_{C}$ and vanishes above this temperature with
disappearance of FM phase. Relaxation of a non-equilibrium magnetic state of
the compound manifests itself through a training effect also observed while
studying EB in Nd2/3Ca1/3MnO3.
