Cr2(NCN)3, a ferromagnetic carbodiimide with an unusual two-step magnetic transition

Abstract

While most transition-metal carbodiimides exhibit antiferromagnetism, chromium(III) carbodiimide, the first transition-metal(III) carbodiimide with a 3d³ configuration, displays ferromagnetic coupling. We report here on a neutron-diffraction study of Cr₂(NCN)₃ demonstrating that a complete three-dimensional ferromagnetic order is established below T = 114 K. Complementary ac and dc susceptibilities as well as electron paramagnetic resonance (EPR) and heat-capacity measurements allow us to further analyze its magnetic properties, elucidating another magnetic transition around T = 160 K. We describe here a magnetic two-step transition scenario over an unusual wide temperature range, from paramagnetic to a lower-dimensional ferromagnetic ordering, presumably a 2D-ordering within the chromium layers, below T_LD = 166(4) K and from this low-dimensional ordering to a complete 3D-ferromagnetic ordering below T_C = 114 K.