Crystal growth, magnetic, and optical properties of the ternary nitride MnSiN2

Single crystals of MnSiN2 have been obtained in dimensions up to several millimeters via a vapor-liquid-solid (VLS) crystal growth mechanism. Detailed single-crystal structure investigations have been carried out. The atomic structure was refined using the space group symmetry Pna2(1) and the unit cell parameters a = 5.2706( 12), b = 6.5206(14), and c = 5.0706(12) angstrom. The crystals were transparent with an intense red color, although only spin-forbidden electronic d-d transitions in high-spin Mn2+ are expected. Optical absorption spectra show a band structure comparable to spectra of Mn2+ in oxide matrixes; however, the absorption bands occur at lower energies and are more intense than expected. This effect is ascribed to a higher degree of covalency for Mn-N bonds. The atomic and magnetic structures have been refined using neutron powder diffraction data collected at room temperature. The magnetic data were collected using a SQUID in the temperature range of 300-700 K in magnetic fields up to 5 T. The paramagnetic region above 500 K contains strong magnetic fluctuations of antiparallel type. Below 490 K, the spins order antiparallel and the magnetic ordering turns into a capped antiferromagnetic state at 442 K with spin tilting disorder.