Origins of ferromagnetism in transition-metal doped Si

Abstract

We present results of the magnetic, structural and chemical characterizations

High-temperature ferromagnetism in Si:Mn alloys

“…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.…”

“…3 and 13, where the presence of a small amount of Mn atoms in the interstitial positions of the Si lattice, as well as the precipitation of Mn-rich nanometer-sized particles (henceforth, nanoparticles) in a Mn-poor silicon matrix, was detected by studying the structural, magnetic, and transport properties of the samples. The temperature-dependent magnetization was characterized by two (≈50 K and ≈250 K) 3 and three [≈45 K, ≈(630-650) K and ≈(805-825) K] 13 different critical temperatures. The authors explained their findings by the presence of various magnetic phases in the samples.…”

Si-Based Magnetic Semiconductors

“…For samples annealed at these high temperatures, precipitates of Mn 3 O 4 were observed on the nanowire surface due to the poor solubility of Mn in Si. A more in-depth investigation of similarly synthesized nanowires found that the magnetic susceptibility displayed several transitions near 45 K, 640 K, and 815 K which were attributed to the formation of Mn 4 Si 7 precipitates, the presence of unintended Fe and Cr impurities, or spinodal decomposition [49].…”

Local structure and magnetic properties of B2- and B20-like ultrathin Mn films grown on Si(001)

“…In addition, the size and shape of the ensuing precipitates are also influenced by the growth conditions and structures such as MnSi 1.7 nanospheres 8 and Mn x Si 1-x nanopipes 9 have been reported. However, the report of T C > 400 ºC 1,2,4,8 is surprising given the low T C of all known bulk Mn-Si phases, which include Mn 3 Si, an antiferromagnet (AF) with a Néel temperature T N =23 K, 10,11 Mn 5 Si 3 (AF, T N =99 K), 12 MnSi (T C =29.5 K) which is a helical magnet (HM), 13 and the higher manganese silicide MnSi 1.7 family (HM, T C ~ 43 K). 14,15 One model attempts to explain the high T C in this condensed magnetic semiconductor as due to an enhancement of the coupling between Mn spins in the Si matrix due to spin-fluctuations in the itinerant MnSi 1.7 precipitates.…”

“…Structural analysis of dilute Mn x Si 1-x attributed the high T C to the co-existence of small Mn clusters and a nanocrystalline MnSi 1.7 phase. 3 A more detailed study later found that MnSi 1.7 likely had an ordering temperature closer to a bulk T C = 47 K and other nanocrystalline phases were responsible for the high T C. 4 Depending on Mn concentration and thermal manipulation during sample growth, precipitates with various Si:Mn phases 5,6 or nanocrystallites with defect MnSi structures 7 are produced. In addition, the size and shape of the ensuing precipitates are also influenced by the growth conditions and structures such as MnSi 1.7 nanospheres 8 and Mn x Si 1-x nanopipes 9 have been reported.…”