Effect of concentration deviation from stoichiometry on the magnetism of Mn_1+δAs_0.75Sb_0.25

Mn_1+δAs_0.75Sb_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_1.00As_0.75Sb_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 5T, 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+δAs _0.75Sb_0.25.