Magnetic properties of crystals of the free organic radical molecule NIT-2Py

NIT-2Py is a purely organic quantum magnet with two inequivalent sites occupied by free radical carryingS = 1/2 moments. From thermodynamics measurements we identified two distinct ordered phases: a three dimensional antiferromagnetic order at TN = 1.32 K in zero field and a field-induced phase reaching a maximal Tc = 0.53 K at 6 T. Interestingly, a magnetization plateau at half saturation is observed at intermediate fields in the disordered state, which can be explained from the polarization of one of the inequivalent sites. On the other site, the molecules form S = 1 dimers with a gap Delta/kB = 8.1 ± 0.2 K which can be suppressed with a magnetic field Hc = 5 T where the field-induced phase emerges. This order can therefore be described as a Bose-Einstein condensation (BEC) of triplet excitations. Due to the crystal structure of NIT-2Py, this BEC lives on dimer planes in between planes of fully polarized spins.

Dr. Andrea Bianchi, Département de Physique, Université de Montréal