Study of MnSb alloy on the range of 43% to 50% of at.%Sb, revealed an unexpected presence of MN2SB phase

The discovery of nonferrous magnetic alloys was reported by Heusler1 in 1898 and since then the investigation and application of these alloys on industrial and scientific devices have been growing continuously. Guillaud2 described a variable Curie Temperature (between 90°C and 314°C) for MnSb alloy, obtained exclusively through the variation of the stoichiometry (from 45% to 49% in atomic percentage of Sb (at.%Sb). At least six different phase diagrams were published, besides the long time from its discovery, they still have some uncertain regions related to minimum/maximum stoichiometry of MnSb phase and its respective Tc. Okamoto’s phase diagram3 defines this region being from 45% and 49% atomic Sb at room temperature up to 314°C, and respective Tc varying from 90°C to 314°C. Crystallographic files from ICSD4 provide references where the phase is described as Mn1.092Sb or Mn1.1Sb. Eight samples, from 43% to 50% at. Sb was produced, covering the complete range of Mn1.092Sb phase. Guillaud 2 reported a tunable magnetic transition through stoichiometry between 90°C to 314°C, Teramoto & Van Run5 confirmed the non dependency of annealing temperature between 400°C and 700°C for 49% atomic of Sb, and plotted a partial phase diagram (Figure 1), where MnSb stable phase varies with temperature from 46 to 50%at of Sb at 400°C, and a single point at 41% atomic Sb (%at.Sb) at 840°C describing a non linear behavior. Teramoto & Van Run5 reported quenching from temperatures between 400°C to 700°C didn’t change the Tc, being independent of annealing or quenching temperature, but only related to stoichiometry. Okamoto3 reported a peritectic transition at 840°C and variable Tc related stoichiometry from 44% to 49% at.Sb. at 400°C. Chen6 identified the peritectic temperature at 843°C and the stoichiometry between 45% and 49.5% atomic of Sb at 400°C, Vanyarkho7 r e p o r t e d the peritectic temperature at 841°C and the MnSb phase from 45% to 49% at 400°C, Williams8 reported the peritectic temperature at 853°C and variable magnetic range from 40% to 50% below 573; and Kainzbauer9 reported the peritectic temperature at 830°C and limits of MnSb phase from 45.5% to 50.5at% of Sb. Although Guillaud2 described the reaction at MnSb alloy as a SOMT (Second Order Magnetic Transition), Nwodo10 reported a FOMT (first order magnetic transition), AFM-FI (Antiferromagnetic→Ferrimagnetic) reaction, attributed to a spin reorientation of Mn2Sb dropped with Sn (Mn2Sb0.9Sn0.1).