Origin of ferromagnetism ofMnSi1.7nanoparticles in Si: First-principles calculations

Abstract

The origin of the magnetism of MnSi 1.7 nanoparticles in Si is investigated using the first-principles calculations: bulk and interface effects are considered. The bulk magnetic property is expected to be affected by stoichiometry, strain, and charge accumulation. Stoichiometry and charge accumulation induce a ferromagnetic state, and strain stabilizes the ferromagnetic state. Another factor, the MnSi 1.7 / Si interface formation, is seen as triggering ferromagnetism strongly localized at the interface. These two mechanisms are shown to be related to the experimentally determined hard and soft components, respectively.

High-temperature ferromagnetism in Si:Mn alloys

“…The magnetic moment of the interfacial Mn calculated in Ref. 20, ≈1μ B per Mn atom, is considerably larger than that in bulk MnSi 1.7 and is rather consistent with that of the interstitial Mn in Si, ≈(2-3)μ B per Mn atom, 21 being nevertheless somewhat smaller than the nominal value, ≈(4-5)μ B per Mn atom, embedded in the GaAs matrix. 18 It is quite clear that the Si:Mn samples display a significant structural disorder, whose detailed characteristics may depend on the way in which the samples are grown.…”

“…For instance, the boundary between the precipitate and the matrix may strongly influence the magnetic characteristics of an individual precipitate nanoparticle. 17,20 Below, we show that the spin-fluctuation scenario for high-temperature ferromagnetism in the finite-size precipitate embedded in the Si matrix is to some extent different from that of the bulk precipitate. We assume here that the interior of a precipitate particle consists of the pure MnSi 1.7 silicide without Mn d defects.…”

“…Firstprinciple calculations 20 clearly indicate that the magnetic state of the MnSi 1.7 silicide is hardly affected by either the strain or the charge transfer which are certainly induced in the nanoparticle. Besides, these calculations suggest an important role of the MnSi 1.7 /Si interface that could be relevant for ferromagnetism in the nanometer-sized precipitate, different from that in the bulk MnSi 1.7 .…”

“…A nontrivial solution exists, provided β ω < 0. In the one-dimensional case, one can readily construct the first integral and give the solution of the nonlinear equation (20) in the explicit form…”

“…We presented these alloys as composed of MnSi 2−z precipitate particles enclosed in the Si matrix. 7,10,17,20 We gave a detailed answer to the crucial question why the magnetization and the Curie temperature of the MnSi 2−z precipitate are much larger, roughly by an order of magnitude, than those of the bulk MnSi 1.7 silicide (Ref. 11).…”