  A new mononuclear Dysprosium based Coordination Polymer {Dy-CP} was
investigated magnetically using dc and ac magnetic susceptibility. The dc
magnetic susceptibility does not exhibit any long-range ordering down to 1.8 K
and the negative value of Curie Constant (~ - 4 K) indicate the dominance of
antiferromagnetic interactions between the Dy (III) spins. Ac susceptibility
exhibits absence of single molecular magnet behavior at zero dc magnetic field
and shows signal of quantum tunneling magnetization (QTM) below 8 K. However,
on the superimposition of dc magnetic field (3 kOe), frequency dependent
relaxation peak emerged at T_f = 5 K and QTM signal suppress at higher fields.
The intermediate value of Mydosh parameter calculated from the shift in peak
position (T_f) in ac susceptibility reflects the formation of superparamagnetic
state. Further, the temperature dependence of Tf is analyzed with Arrhenius and
Cole-Cole plot. The magnetic susceptibility analysis yields characteristics
pre-relaxation factor 1.40x10^(-12) sec and energy barrier {\Delta}E/k_B = 93.4
K, indicating the slow spin relaxation. The Cole-Cole fit to the ac
susceptibility data shows further evidence for the single ion spin relaxation.
Thus, the magnetic measurements support the single-molecule magnet behavior in
Dy-CP under the application of dc magnetic field.
