Manganese monosilicide (MnSi) is an intermetallic compound, a

silicide A silicide is a type of chemical compound that combines silicon and a usually more electropositive element. Silicon is more electropositive than carbon. In terms of their physical properties, silicides are structurally closer to borides than t ...

manganese Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...

. It occurs in

cosmic dust Cosmic dustalso called extraterrestrial dust, space dust, or star dustis dust that occurs in outer space or has fallen onto Earth. Most cosmic dust particles measure between a few molecules and , such as micrometeoroids (30 μm). Cosmic dust can ...

as the mineral brownleeite. MnSi has a cubic crystal lattice with no

inversion center In geometry, a point reflection (also called a point inversion or central inversion) is a geometric transformation of affine space in which every point is reflected across a designated inversion center, which remains fixed. In Euclidean or ...

; therefore its crystal structure is helical, with right-hand and left-hand chiralities. MnSi is a

paramagnetic Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, ...

metal A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...

that turns into a

ferromagnet Ferromagnetism is a property of certain materials (such as iron) that results in a significant, observable magnetic permeability, and in many cases, a significant magnetic coercivity, allowing the material to form a permanent magnet. Ferromag ...

at cryogenic temperatures below 29 K. In the ferromagnetic state, the spatial arrangement of electron spins in MnSi changes with magnetic field, forming helical, conical,

skyrmion In particle theory, the skyrmion () is a topologically stable field configuration of a certain class of non-linear sigma models. It was originally proposed as a model of the nucleon by (and named after) Tony Skyrme in 1961. As a topological solito ...

, and regular ferromagnetic phases.

Crystal structure and magnetism

Manganese monosilicide is a

non-stoichiometric compound Non-stoichiometric compounds are chemical compounds, almost always solid inorganic compounds, having elemental composition whose proportions cannot be represented by a ratio of small natural numbers (i.e. an empirical formula); most often, in s ...

, meaning that the 1:1 Mn:Si composition, lattice constant and many other properties vary depending on the synthesis and processing history of the crystal. MnSi has a cubic crystal lattice with no

; therefore its crystal structure is helical, with right-hand and left-hand chiralities. At low temperatures and magnetic fields, the magnetic structure of MnSi can be described as a stack of ferromagnetically ordered layers lying parallel to the (111) crystallographic planes. The direction of

magnetic moment In electromagnetism, the magnetic moment or magnetic dipole moment is the combination of strength and orientation of a magnet or other object or system that exerts a magnetic field. The magnetic dipole moment of an object determines the magnitude ...

varies from layer to layer by a small angle due to the antisymmetric exchange. Upon cooling to temperatures below T_c = 29 K, MnSi changes from a

into a

ferromagnetic Ferromagnetism is a property of certain materials (such as iron) that results in a significant, observable magnetic permeability, and in many cases, a significant magnetic coercivity, allowing the material to form a permanent magnet. Ferromagne ...

state; the transition temperature T_c decreases with increasing pressure, vanishing at 1.4 GPa. Electron spins in MnSi show dissimilar, yet regular spatial arrangements at different values of applied magnetic field. Those arrangements are named helical,

, conical, and regular ferromagnetic. They can be controlled not only by temperature and magnetic field, but also by

electric current An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...

, and the current density required for manipulating skyrmions (~10⁶ A/m²) is approximately one million times smaller than that needed for moving

magnetic domain A magnetic domain is a region within a magnetic material in which the magnetization is in a uniform direction. This means that the individual magnetic moments of the atoms are aligned with one another and they point in the same direction. When c ...

s in traditional ferromagnets. As a result, skyrmions in MnSi have potential application in ultrahigh-density

magnetic storage Magnetic storage or magnetic recording is the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetisation in a magnetizable material to store data and is a form of non-volatile memory. The information is acc ...

devices.

Synthesis

Centimeter-scale single crystals of MnSi can be prepared by direct crystallization from the melt using the Bridgman,

zone melting Zone melting (or zone refining, or floating-zone method, or floating-zone technique) is a group of similar methods of purifying crystals, in which a narrow region of a crystal is melted, and this molten zone is moved through the crystal. The molt ...

Czochralski method The Czochralski method, also Czochralski technique or Czochralski process, is a method of crystal growth used to obtain single crystals (monocrystals) of semiconductors (e.g. silicon, germanium and gallium arsenide), metals (e.g. palladium, platin ...

References

{{Silicides Manganese compounds Transition metal silicides Iron monosilicide structure type