Study by Mössbauer spectroscopy of arsenides Fe2−xMnxAs

The study by Mössbauer spectroscopy of the Fe_2?xMn_xAs series confirms that the iron atom completely occupies site I of the structure and leads to Néel temperatures in aggeement with those deduced from magnetic susceptibility measurements. In the range x = 0.8 to x = 1.4, the hyperfine structure is unresolved. On passing from Fe₂As to Mn₂As, three types of magnetic structures are encountered; contrary to the conclusion drawn from neutron diffraction measurements, the spins in Mn₂As are not perpendicular to the c-axis, and FeMnAs does not have the magnetic structure of Mn₂As.The internal magnetic field curves as a function of temperature are in this series either over-Brillouin with first-order antiferromagnetic (AF) to paramagnetic (P) transition or under-Brillouin. In order to explain the set of the observed magnetic anomalies, the existence of itinerant magnetism is postulated.