Eur. Phys. J. B (2012) 85: 149
https://doi.org/10.1140/epjb/e2012-30034-2

Regular Article

Half-metallic spin polarized electron states in the chimney-ladder higher manganese silicides MnSi_1−x (x = 1.75 − 1.73) with silicon vacancies

¹ Dipartimento di Fisica, Università di Roma “La Sapienza”, Piazzale Aldo Moro 2, 00185 Roma, Italy
² A.M. Prokhorov General Physics Institute, Vavilov str. 38, 119991 Moscow, Russia
³ RRC Kurchatov Institute, Kurchatov Sqr. 1, 123182 Moscow, Russia

^a e-mail: sergio.caprara@romal.infn.it

Received: 12 January 2012
Received in final form: 13 February 2012
Published online: 15 May 2012

Abstract

The electronic and optical properties of the higher manganese silicides, known as the Nowotny “chimney-ladder” phases, are investigated by means of first-principles density-functional calculations and compared with the experimental results. According to our calculations, Mn₄Si₇ is an intrinsic semiconductor and a nonmagnetic material, while Mn₁₁Si₁₉ and Mn₁₅Si₂₆ are metals and half-metallic weak ferromagnets, in agreement with recent experimental findings. The role of intrinsic lattice defects, namely vacancies, common for such open crystal structures, is clarified. The vacancies in Mn₄Si₇ lead to a metallization of the electronic spectrum and to a magnetic state of half-metallic nature. In Mn₁₁Si₁₉ and Mn₁₅Si₂₆ an effect of vacancies is that the average magnetic moment per Mn atom is almost four times larger than that in stoichiometric higher manganese silicides. The origin of this magnetic moment enhancement is explained by the variation of the Mn coordination numbers. The calculated optical spectra are in good agreement with available experimental data. We find a relatively high (1.2°) polar magneto-optical Kerr effect in Mn₁₁Si₁₉ and Mn₁₅Si₂₆ in the infrared region 0.1−0.3 eV. It is shown that such magneto-optical peaks are formed by the low energy plasmons.