Manganese Monosilicide Research Articles

Electron paramagnetic resonance probing of the spin fluctuation transition in the conical spiral phase of MnSi

In the spiral conical phase of manganese monosilicide, MnSi, the EPR spectra are studied at a frequency of 9.3 GHz in the temperature range of 5–30 K for an external magnetic field oriented along the crystallographic direction [100]. It is found that in the temperature range T < T* = 25 K, located 4 K below the paramagnetic phase-conical phase transition temperature TC = 29 K, a complex EPR spectrum consisting of several lines appears. A procedure is proposed for decomposing experimental spectra into components, which makes it possible to find for each spectral line the temperature dependences of the resonance magnetic field, line width, and integrated intensity. At Tf ∼16 K, one of the main lines in the EPR spectrum with the highest integrated intensity demonstrates a maximum in the temperature dependence of the line width W(T), corresponding to a change in W by a factor of ∼2.8. We argue that this unusual behavior appears as a consequence of a spin fluctuation transition in the conical spiral magnetic phase with long range magnetic order.

Spin Fluctuations and a Spin-Fluctuation Phase Transition in the Magnetically Ordered Phase of Manganese Monosilicide

Spin Fluctuations and a Spin-Fluctuation Phase Transition in the Magnetically Ordered Phase of Manganese Monosilicide

Phase Transitions in Helicoidal Ferromagnets with Concentrational Fluctuations of Local Magnetization

A phenomenological approach to the theory of phase transitions induced by fluctuations in helicoidal ferromagnets with concentrational fluctuations is developed. For this purpose, random variables equal to one at a site ν occupied by a magnetic atom and zero otherwise are introduced into the Ginzburg–Landau functional. It is shown that, above the magnetic transition temperature (TC), due to concentrational effects, local magnetization is preserved, fluctuations of the helicoidal spin helix arise, and skyrmion states in the magnetic field are formed. The disappearance of the vortical states is due to the suppression of local magnetization by thermodynamic fluctuations at the temperature TS (>TC). The theoretical results explain the reasons for the significant expansion of the temperature range of skyrmion states in nonstoichiometric manganese monosilicide with manganese deficiency.

Фазовые переходы в геликоидальных ферромагнетиках с концентрационными флуктуациями локальной намагниченности

A phenomenological description of phase transitions induced by fluctuations in helicoidal ferromagnets with concentration fluctuations has been developed. For this, the method of the Ginzburg-Landau functional was used and random variables that are equal to unity in the place occupied by the magnetic atom and zero otherwise are introduced. It is shown that, due to concentration effects, the local magnetization is preserved above the temperature of the magnetic transition (TS), fluctuations of the spin spiral arise, and skirmion states arise in a magnetic field. The disappearance of vortex states is associated with the suppression of local magnetization by thermodynamic fluctuations at temperature TS (&gt; TC). Theoretical results explain the reasons for the significant expansion of the temperature range of states of the skyrmion in a non-stoichiometric manganese monosilicide with manganese deficiency.

The dependence of the microstructure and thermoelectric properties of germanium-doped higher manganese silicide crystals

The reason why manganese monosilicide inclusions are formed during the growth of higher manganese silicide (HMS) crystals has not been studied in detail so far. Changes in the amount and density of these inclusions are greatly influenced by dopants. In this study, the structure of HMS crystals with various contents of germanium as a doping element is examined. It is found that raising the germanium content to 1 at % results in the fragmentation of layered manganese monosilicide inclusions and, simultaneously, leads to significant changes in the thermoelectric properties of HMS crystals. The results of the microstructural analysis of HMS crystals in relation to the germanium concentration may be of use for understanding the mechanism by which the manganese monosilicide phase is formed during the growth of higher manganese silicide crystals.

Formation of manganese silicides on the Si(111)7 × 7 surface

The initial stages of the growth of manganese films on the Si(111)7 × 7 surface at room temperature and reactions of solid-phase synthesis of manganese silicides, which occur during annealing these films in the temperature range up to 600°C, have been investigated using high-energy-resolution photoelectron spectroscopy with synchrotron radiation. It has been shown that the deposition of manganese on the silicon surface leads to the formation of interfacial manganese silicide and a film of the silicon solid solution in manganese. The growth of a metallic manganese film begins after the deposition of ∼6 A Mn. The segregation of silicon is observed in the coverage range of 17 A Mn. The annealing of the sample with a coverage of 25 A Mn in the temperature range of 200–400°C leads to the formation of a Mn-Si solid solution and manganese monosilicide. A further increase in the temperature to 600°C results in the transformation of MnSi into the semiconductor silicide MnSi1.7.

Solid-phase synthesis of manganese silicides on the Si(100)2 × 1 surface

The solid-phase synthesis of manganese silicides on the Si(100)2 × 1 surface coated at room temperature by a 2-nm-thick manganese film has been investigated using high-energy-resolution photoelectron spectroscopy with synchrotron radiation. The dynamics of variation of the phase composition and electronic structure of the near-surface region with increasing sample annealing temperature to 600°C, has been revealed. It has been shown that, under these conditions, a solid solution of silicon in manganese, metallic manganese monosilicide MnSi, and semiconductor silicide MnSi1.7 are successively formed on the silicon surface. The films of both silicides are not continuous, with the fraction of the substrate surface occupied by them decreasing with increasing annealing temperature. The binding energies of the Si 2p and Mn 3p electrons in the compounds synthesized have been determined.

Precipitates of MnSi cubic phase in tetragonal Mn4Si7 crystal

Higher manganese silicides (HMSs) exhibit interesting thermoelectric and optoelectronic properties. Development of HMS-based thermoelements and microthermopiles of different designs may meet a number of problems, which can be solved only when the real structure of crystals and thin layers on which they are based is established. We have applied scanning and transmission electron microscopy and electron diffraction to investigate HMS crystals of two types: single crystals grown from melt by the Bridgman method and microislands formed by reactive diffusion during manganese vapor deposition on silicon substrates. The exact phase composition of these materials is established: matrix HMS crystal belonging to tetragonal system (Mn4Si7 composition) and precipitates of cubic manganese monosilicide MnSi. The shape and sizes of precipitates are determined, the crystallographic relationships between the tetragonal and cubic phases are found, and the interface is investigated.

Defect-induced high-temperature ferromagnetism in Si1-xMnx(x ≈ 0.52−0.55) alloys

We present a comparative study of the anomalous Hall effect (AHE) and of the transverse Kerr effect (TKE) in the nonstoichiometric alloys. The data on AHE and TKE are consistent with each other and clearly indicate the intrinsic above room-temperature ferromagnetic order in the studied samples. We argue that this order is not produced by the phase segregation effects, but rather has a global character, while even a small level of the nonstoichiometry in alloys drastically changes their magnetic, electrical, optical and magneto-optical properties as compared to those of the stoichiometric manganese monosilicide MnSi. We propose a qualitative explanation of the obtained experimental results in the frame of the model of defect-induced ferromagnetic order using the first-principles calculations of the electronic and magnetic structure of the system.

High-temperature ferromagnetism in Si1 − x Mn x (x ≈ 0.5) nonstoichiometric alloys

It has been found that the Curie temperature (T C ≈ 300 K) in nonstoichiometric Si1 − x Mn x alloys slightly enriched in Mn (x ≈ 0.52–0.55) in comparison to the stoichiometric manganese monosilicide MnSi becomes about an order of magnitude higher than that in MnSi (T C ∼ 30 K). Deviations from stoichiometry lead to a drastic decrease in the density of charge carries (holes), whereas their mobility at about 100 K becomes an order of magnitude higher than the value characteristic of MnSi. The high-temperature ferromagnetism is ascribed to the formation of defects with the localized magnetic moments and by their indirect exchange interaction mediated by the paramagnetic fluctuations of the hole spin density. The existence of defects with the localized magnetic moments in Si1 − x Mn x alloys with x ≈ 0.52–0.55 is supported by the results of numerical calculations performed within the framework of the local-density-functional approximation. The increase in the hole mobility in the nonstoichiometric material is attributed to the decay of the Kondo (or spin-polaron) resonances presumably existing in MnSi.

Thermoelectric Properties of Manganese Monosilicide Synthesized by Mechanical Alloying Process

Manganese silicide is one of the potential thermoelectric materials for high temperature application. As a fundamental investigation on these materials group, manganese monosilicides were synthesized by the mechanical alloying of stoichiometric elemental powder compositions, and the as-milled powders were consolidate by vacuum hot pressing. Phase transformation and microstructure evolution during mechanical alloying and hot consolidation were investigated using XRD and SEM. Near single phase of monosilicides were successfully produced in this process. Thermoelectric properties as a function of temperature were evaluated in terms of Seebeek coefficient, electrical resistivity, thermal conductivity and the figure of merit for the hot pressed specimens. Mechanically alloyed manganese monosilicide, MnSi, appeared to have a potential as a thermoelectric material in this study.

Is MnSi an itinerant-electron magnet? Results of ESR experiments

High-frequency (60 GHz) electron spin resonance (ESR) has been studied in manganese monosilicide, MnSi, single crystals. The measurements performed within the 4.2–300 K temperatures range at the applied magnetic field up to 70 kOe have demonstrated that the magnetic resonance in MnSi is due to localized magnetic moments of the Heisenberg type with the g-factor depending only slightly on temperature, g ∼ 1.9–2. At the same time, it has been found that the ESR linewidth is determined by spin fluctuations and can be quantitatively described in the wide temperature range (4.2 K < T < 60 K) in the framework of the Moriya theory using the S L (T) function. The revealed deviations from the model of weak itinerant-electron magnetism commonly used for the description of the magnetic properties of MnSi indicate a possible spin-polaron nature of the unusual magnetic properties of this strongly correlated metal.

Two-dimensional fractal-like growth on semiconductors: The formation of continuous manganese monosilicide ultrathin films on Si(111)

Continuous crystalline MnSi ultrathin films with atomically flat surfaces, which are highly expected to find an application in Si-based spintronics, are grown on Si(111)-7×7 by solid phase epitaxy method. The interfacial reaction between Mn and Si and the formation processes of the films as well as their morphological variation with annealing temperature are investigated using scanning tunneling microscopy. The MnSi ultrathin films form in a two-dimensional (2D) fractal-like mode only at a Mn coverage above ∼2 ML and at an annealing temperature in the narrow range of ∼250–300 °C. Above ∼300 °C, the growth mode gradually transforms into Volmer–Weber mode and correspondingly, the continuous films transform into 2D compact islands. The films grow with a thickness unit of quadruple layer, which is consistent with the B20-type MnSi structure.

Signature of Helimagnetic Ordering in Single-Crystal MnSi Nanowires

We report the synthesis, structural characterization, and magnetotransport of single-crystalline nanowires of manganese monosilicide, MnSi. Bulk MnSi has unusual magnetic orderings, helimagnetism, and skyrmions at ambient pressure, and high pressure studies have revealed partial magnetic ordering and non-Fermi liquid behavior. MnSi nanowires were synthesized using chemical vapor deposition of MnCl(2) onto silicon substrates. The morphology, structure, and composition of these nanowires were analyzed using electron microscopy and X-ray spectroscopy. The low-temperature magnetoresistance characteristics of MnSi nanowires reveal the first signature of helimagnetism in one-dimensional nanomaterials.

X-ray photoelectron spectroscopic studies on initial oxidation of iron and manganese mono-silicides

Initial oxidation of iron and manganese mono-silicides (FeSi and MnSi) surfaces was studied by X-ray photoelectron spectroscopy (XPS). Clean surfaces of these silicides were prepared by fracturing in an ultra high vacuum, and then the fractured surfaces were oxidized by exposing to high-purity oxygen at pressures up to 1.3 Pa. For the clean FeSi surface, positive chemical shifts of the Fe 2p 3/2 and Si 2p peaks from elemental Fe and Si were 0.5 eV and 0.1 eV, respectively. For the clean MnSi surface, a negative chemical shift of the Si 2p peak from elemental Si was 0.1 eV. Iron on the FeSi surface was oxidized at an oxygen pressure of 1.3 Pa, whereas the silicon was oxidized under the pressure of 1.3 × 10 −6 Pa, indicating that oxidation of silicon occurred prior to that of iron. Manganese and silicon on the MnSi were simultaneously oxidized in the range from 1.3 × 10 −6 Pa to 1.3 × 10 −3 Pa; however, over the pressure of 1.3 Pa, the oxidation of manganese occurs prior to that of silicon. These oxidation behaviors at low oxygen pressures were similar to those of the FeSi and MnSi fractured in air.

Physicochemical interaction at the contact of higher manganese silicide with chromium

Diffusion processes taking place at the contact of higher manganese silicide MnSi1.71−1.75 with chromium at elevated temperatures are considered. The microstructures of cast and annealed samples show a diffusion region that evolves at the HMS/Cr interface during the HMS melt crystallization on chromium flakes. As the temperature and time of annealing of HMS/Cr samples increase, the diffusion region grows thicker and new phases appear. It is shown that the diffusion is of reaction character. The diffusion coefficients of magnesium, chromium, and silicon in the solid solution based on manganese and chromium monosilicides and in the solid solution based on the Cr3Si compound are calculated. It is also shown that, when the temperature of the HMS used as a thermoelement positive leg is optimal, the depletion time of a 10-µm-thick chromium layer exceeds 15000 h. Intermetallic phases forming in the diffusion region between the HMS and Cr are of metallic conduction and exhibit a high thermal conductivity, which minimizes energy losses in the contact layers of thermoelements.

Magnetostrictive strains in weak band ferromagnets based on 3d metal monosilicides

The relative volume variables [ω(H, T)] caused by magnetostrictive strains in alloys of solid solutions of manganese, iron, and cobalt monosilicides are studied over a wide range of magnetic fields and temperatures. The results are discussed within the framework of spin-fluctuation theory. The observed anomalies in ω(H, T) are shown to be linked to the growth and saturation of the amplitude of the spin fluctuations.

Temperature-induced local magnetic moments (TILMM) in monosilicides of 3d transition metals

Features of the formation of temperature-induced local magnetic moments (TILMM) and their influence on the magnetic and thermophysical characteristics of iron, cobalt, and manganese monosilicides are investigated. The results obtained for magnetic susceptibility and specific heat measurements are discussed within the framework of spin-fluctuation theory. Temperature-concentration dependences are established for the TILMM absolute value for mutual solid solutions Fe1−xCoxSi and Fe1−yMnySi. It is shown that for a number of the alloys studied the saturation of the TILMM absolute value does not occur, while the anomalous behavior of the polytherm of their physical properties is associated with features of the band structure.

Electronic specific heat of chromium, manganese, and cobalt monosilicides

Electronic specific heat of chromium, manganese, and cobalt monosilicides

Electronic energy band in chromium, manganese, and iron monosilicides

Electrical conductivity, thermoelectromotive force, and Hall coefficient of monosilicides of chromium, manganese, and iron were measured within the range of temperature from 80 to 400‡K. The obtained values of the transfer factor were applied for calculation of characteristic parameters in the normal and narrow band models.