  Each single domain nano-magnet acts as a magnetic dipole in addition it
oscillates its magnetization about the easy axis and rotates coherently
depending upon temperature and anisotropy. In an ensemble of nano-magnets, the
relaxation time of a nano-magnet tunes with the long range dipolar interaction
which in turn is determined by the particle size, density and the number of
nano-magnets present in the ensemble. Hence, the aggregation of interacting
nano-magnetic dipoles, demonstrates both experimentally and theoretically as a
model system to detect intriguing co-operative physical phenomena. Here we show
a new variant of phase transition from paramagnetic to diamagnetic phase by
changing the frequency of the applied sinusoidal magnetic field for a
nano-magnetic ensemble. This phenomenon unravels a new insight of physics and
it may be significant on the design and development of magnetic devices. The
simulation of the system is well in agreement with the experimental results.
