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 exam ined 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 ferr omagnetic based on the Stoner criterion, and how the ferromagnetism of the 22-electron ABX compounds differs from that of the 17- and 19-electron anal ogs. To a first approximation, the electronic structure of ABX with 18 or m ore 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 com pound the d-electron count for the electronegative transition metal B is cl ose to d(10). The ferromagnetism of the 17- and 19-electron ABX compounds i s 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 loc alize. (C) 2000 Elsevier Science B.V. All rights reserved.