Study of the 18-electron band gap and ferromagnetism in semi-Heusler compounds by nea-spin-polarized electronic band structure calculations

Based on non-spin-polarized electronic band structure calculations, we examined why the electronic structure of a semi-Heusler compound ABX has the 18-electron band gap, why 17-and 19-electron ABX compounds can be weakly ferromagnetic based on the Stoner criterion, and how the ferromagnetism of the 22-electron ABX compounds differs from that of the 17- and 19-electron analogs. To a first approximation, the electronic structure of ABX with 18 or more valence electrons is described in terms of the d(10) ion for B, the s(2)p(6) ion for X, and the d(n) ion for A (n = 0, 1 and 4 for the case of 18, 19 and 22 valence electrons, respectively). Even for a 17-electron ABX compound the d-electron count for the electronegative transition metal B is close to d(10). The ferromagnetism of the 17- and 19-electron ABX compounds is explained in terms of the Stoner criterion, and that the 22-electron ABX compounds by the strong tendency for the d-electrons of the d(4) ion to localize. (C) 2000 Elsevier Science B.V. All rights reserved.