MnSi1.7nanoparticles embedded in Si: Superparamagnetism with collective behavior

Abstract

The doping of Mn in Si is attracting research attentions due to the possibility to fabricate Si-based diluted magnetic semiconductors. However, the low solubility of Mn in Si favors the precipitation of Mn ions even at nonequilibrium growth conditions. MnSi 1.7 nanoparticles are the common precipitates, which show exotic magnetic properties in comparison with the MnSi 1.7 bulk phase. In this paper we present the static and dynamic magnetic properties of MnSi 1.7 nanoparticles. Using the Preisach model, we derive the magnetic parameters, such as the magnetization of individual particles, the distribution of coercive fields and the interparticle interaction field. Time-dependent magnetization measurements reveal aging and memory effects, qualitatively similar to those seen in spin glasses.

High-temperature ferromagnetism in Si:Mn alloys

“…39,40 In contrast to the above scenario, bulk MnSi 1.7 silicide shows weak itinerant magnetism with an ordering temperature of 47 K and with a very low saturation moment of 0.012μ B /Mn, 11 which are much different from those of the MnSi 2−z nanoparticles in the Si 1−x Mn x materials. 10,17 The mechanism for high-temperature FM ordering in the MnSi 2−z precipitate due to spin fluctuations is presented in our work. Note that the saturation moment for the MnSi 2−z precipitate ( 0.2μ B /Mn) is much smaller than that for Mn 5 Ge 3 .…”

“…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).…”

“…41-44, dedicated to this important topic. As far as an ensemble of nanomagnets is concerned, at sufficiently high temperatures (but, obviously, below the temperature of FM transition inside the precipitate) the superparamagnetic behavior of the particles is almost evident, 10 but in the low-temperature region, the FM alignment of magnetic moments of different particles is possible. On the other hand, the blocking of these moments by the matrix and the formation of a cluster-glass state may not be excluded.…”

“…Such a behavior indicated that only a small fraction of doped Mn atoms give rise to the magnetization, whereas the majority of Mn atoms are magnetically inert (contrary to the general belief that a localized moment exists on Mn in Si). The low-temperature ferromagnetism, with a saturation moment of ≈0.21μ B per Mn atom, observed in a number of works, [7][8][9][10] 035201-1 1098-0121/2011/83(3)/035201 (13) ©2011 American Physical Society was attributed to nanometer-sized precipitates of the so-called tetragonal phase MnSi 1.7 . This phase is known to include several stoichiometric silicide compounds Mn n Si m , with m/n ≈ 1.…”

Direct observation of the lattice sites of implanted manganese in silicon

“…2,3, 12,13,16 In that respect, a detailed study of the lattice sites occupied by implanted Mn in the phase-pure regime (dilute, randomly distributed Mn) should clarify whether this is indeed the case. We have addressed these questions by applying the electron emission channeling technique (EC) from implanted radioactive 56 Mn probes to different doping types of Si single crystals.…”