  In this study we examine the phase transitions in single crystals of
[(CH3)2NH2]Co(HCOO)3], using magnetization and specific heat measurements as a
function of temperature and magnetic field. Magnetisation measurements indicate
a transition at 15 K that is associated with an antiferromagnetic transition.
The results of the isothermal magnetization versus magnetic field curves
demonstrate the presence of a single-ion magnet phase, coexisting with
antiferromagnetism. A peak in specific heat is seen at 15 K, corresponding to
the magnetic transition. The enthalpy of the transition evaluated from the area
under the specific heat peak decreases with the application of magnetic field
of upto8 T. This is suggestive of long range antiferromagnetic magnetic order,
giving way to single-ion magnetic behavior under external field. In experiments
at high temperatures, corresponding to the well-known structural transition in
this system, the specific heat measurements, shows a peak at ~155K, that is
insensitive to applied magnetic field. The magnetisation in this temperature
range, while it exhibits a paramagnetic behavior, shows a distinct jump that
has been attributed to a spin-state transition of Co2+ associated with the
structural transition.
