Electronic, structural and magnetic properties of Mn(1+x)Pt(1-x)Sb

•The electronic properties of Mn(1+x)Pt(1-x)Sb (0 ≤ x ≤ 0.5) alloys have been investigated.•MnPtSb is nearly half metallic but the Mn-rich alloys show robust half-metallicity.•MnPtSb and Mn1.75Pt0.75Sb have been synthesized and investigated.•The experimental results of both samples agree well with the theoretical predictions.•Our results indicate that Mn1.25Pt0.75Sb may be useful for spintronic applications. Electronic and magnetic properties of half-metallic Heusler alloys can be modified by tuning their chemical compositions. We have carried out a combined theoretical and experimental investigation of Mn(1+x)Pt(1-x)Sb (0 ≤ x ≤ 0.5) alloys. Our first-principles calculations indicate that the stoichiometric MnPtSb exhibits nearly half-metallic band structure, but a robust half-metallicity can be achieved in Mn-rich compositions Mn(1+x)Pt(1-x)Sb (0 ≤ x ≤ 0.5) with x = 0.25 and higher in their cubic structures. In addition, while MnPtSb exhibits ferromagnetic alignment, Mn(1+x)Pt(1-x)Sb are ferrimagnetic for all non-zero values of x. We have also synthesized cubic MnPtSb and Mn1.25Pt0.75Sb alloys using arc melting and annealing. The magnetic properties of these alloys are consistent with our theoretical predictions. These results indicate that the Mn-rich Mn(1+x)Pt(1-x)Sb alloys have potential for spin-transport-based devices.