New antiferromagnetic properties of manganese gallium sulfides MnGa2S4-α and MnGa2S4-β

The α and β phases of MnGa₂S₄-α and β have been prepared and characterized. Single crystals of the α-phase have been grown by the vapor phase transport method ; their structure found monoclinic, space group C 2/c, has been refined by the X-ray technique and the positional and thermal parameters are reported. Both compounds are antiferromagnetic with Néel temperatures of 23.5 K and 11 K, for α and β respectively. EPR spectra show a single line, exchange-narrowed at 300 K, with a strong critical broadening above T_N. These results are discussed in relation with the crystal structure and the possible superexchange interactions between the Mn²⁺.