Effect of concentration deviation from stoichiometry on the magnetism of Mn1+δAs0.75Sb0.25

Abstract Mn 1+ δ As 0.75 Sb 0.25 samples with excess Mn content of 0.00 ⩽ δ ⩽ 0.11 were synthesized and subjected to the identification of the phases and the magnetic measurements. The stoichiometric Mn 1.00 As 0.75 Sb 0.25 alloy consisted of two phases with mainly the NiAs-type structure leaving a small amount of Sb as a secondary phase. The samples with δ ⩾ 0.05 formed a single phase with the NiAs-type structure. These results suggest that some Mn atoms occupy the interstitial site of the NiAs-type structure, as observed in the case of Mn 1+ δ Sb. The Curie temperature and the magnetic moment were decreased with the increase of the excess Mn content and the transition from a ferromagnetic to paramagnetic state turned much broader. The magnetic entropy change, which is estimated from the magnetization vs. temperature curve, was reduced drastically when δ ⩾ 0.08 . No field-induced magnetic transition was observed for δ ⩾ 0.08 in the magnetization curve up to 5 T, though the compounds with 0.00 ⩽ δ ⩽ 0.05 exhibited such a transition from a paramagnetic to ferromagnetic state just above T C . These results indicate that interstitial Mn atoms have a significant effect on the magnetism of Mn 1+ δ As 0.75 Sb 0.25 .