  We have studied the magnetic properties of three phenalenyl based organic
neutral radicals. The first one is a Heisenberg chain antiferromagnet with one
unpaired spin per molecule; second one is a diamagnetic, exhibiting a
diamagnetic to paramagnetic phase transition at high temperature; the third one
comprises of free neutral radicals and shows paramagnetic behaviour.
Temperature dependent magnetic susceptibility measurements and isothermal
magnetization measurements (as a function of magnetic field) were performed on
all the three systems. In the case of the antiferromagnetic system, temperature
dependent susceptibility and magnetization isotherms were fitted to the Bonner
Fisher model. In the case of second system the diamagnetic to paramagnetic
phase transition is investigated by performing isothermal magnetization
measurements in the two different phases. The diamagnetic to paramagnetic phase
transition seems to be of first order in nature.
