Iron germanide

{{chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = | ImageFile=MnSi lattice2.png | ImageCaption = Structures of left-handed and right-handed FeGe crystals (3 presentations, with different numbers of atoms per unit cell; orange atoms are Ge) | IUPACName = Iron germanide | OtherNames = |Section1={{Chembox Identifiers | CASNo = 12062-73-6 | CASNo_Ref = {{cascite|correct|CAS}} | PubChem = 14619981 | UNII = | DTXSID = DTXSID20779605 | InChI =1S/Fe.Ge | InChIKey =GDXUDZHLHOBFJH-UHFFFAOYSA-N | SMILES =[Fe].[Ge] | ChemSpiderID = | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} }} |Section2={{Chembox Properties | Formula = FeGe | MolarMass = 128.47 g/mol | Appearance = | Density = | MeltingPtC = | MeltingPt_ref = | BoilingPt = | Solubility = | BandGap = }} |Section3={{Chembox Structure | CrystalStruct = Cubic<ref name=r1/> | SpaceGroup = P2₁3 (No. 198), cP8 | LattConst_a = 0.4689 nm | UnitCellFormulas = 4 }} |Section7={{Chembox Hazards | ExternalSDS = | MainHazards = | FlashPt = Non-flammable }} |Section8={{Chembox Related | OtherAnions =Iron silicide | OtherCations =Manganese germanide }} }} '''Iron germanide''' ('''FeGe''') is an intermetallic compound, a germanide of iron. At ambient conditions it crystallizes in three polymorphs with monoclinic, hexagonal and cubic structures. The cubic polymorph has no inversion center, it is therefore helical, with right-hand and left-handed chiralities.<ref name=r1/>

==Magnetism== thumb|upright=1.2|left|Experimental phase diagrams when the applied magnetic field H is directed perpendicular or parallel to a FeGe thin film. With increasing magnetic field, the magnetic ordering of FeGe spins changes from helical (H) to skyrmion (SkL), conical (C) and field polarized (FP, i.e. regular ferromagnetic). [[File:FeGe magnetic phase diagram2a.png|thumb|upright=1.2|left|Simulated and measured (by STXM) images of helical, skyrmion and conical phases. Scale bar: 200 nm]] FeGe is extensively studied for its unusual magnetic properties. Electron spins in this material show dissimilar, yet regular spatial arrangements at different values of applied magnetic field. Those arrangements are named helical, skyrmion lattice, and conical. They can be controlled not only by temperature and magnetic field, but also by electric current, and the current density required for manipulating skyrmions (~10⁶ A/m²) is approximately one million times smaller than that needed for moving magnetic domains in traditional ferromagnets. As a result, skyrmions have potential application in ultrahigh-density magnetic storage devices.<ref name=r2/>

The helical, conical and skyrmion structures are not unique to FeGe; they are also found in MnSi, MnGe and similar compounds, but contrary to those materials, the observation of magnetic ordering patterns in FeGe does not require cryogenic cooling.<ref name=r2/> The disadvantage of FeGe over MnSi is its polymorphism, which hinders the growth of large homogeneous crystals.<ref name=r1/>

==Synthesis==

=== Polycrystalline FeGe === Polycrystalline FeGe is produced by vacuum arc remelting, spark plasma sintering, or high-pressure high-temperature treatment of a mixture of elemental iron and germanium. Single crystals of FeGe ca. 1 mm in size can be grown from the powder using a chemical transport reaction and iodine as transporting agent. The source temperature is maintained at 450 °C and the temperature gradient at ca. 50 °C across the reaction tube, over 1–2 weeks.<ref name="r3" /><ref name="r4" />

=== FeGe thin film === FeGe films can be epitaxially grown on Si (111) using MBE. The thin film FeGe is polycrystalline with ± 30° in-plane rotations around [111] out-of-plane axis.<ref name=":0">{{Cite journal|last1=Wang|first1=Binbin|last2=Bagués|first2=Núria|last3=Liu|first3=Tao|last4=Kawakami|first4=Roland K.|last5=McComb|first5=David W.|date=2022-01-01|title=Extracting weak magnetic contrast from complex background contrast in plan-view FeGe thin films|journal=Ultramicroscopy|language=en|volume=232|article-number=113395|doi=10.1016/j.ultramic.2021.113395|pmid=34653891 |s2cid=239003196 |issn=0304-3991|doi-access=free}}</ref> Theoretical simulations indicate that FeGe thin film can hold skyrmion cylinder or chiral bobber phases, which were recently imaged in a 35 nm plan-view FeGe thin film using Lorentz STEM/TEM.<ref name=":0" />

==Structure== Iron germanide is a non-stoichiometric compound where the Ge:Fe ratio often deviates from 1. The Fe₂Ge₃ compound is a Nowotny phase exhibiting a chimney ladder structure. It is a semiconductor with a band gap or 0.03 eV.<ref name=r5/>

==References== <references>

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</references>

{{Iron compounds}} Category:Iron compounds Category:Germanides Category:Iron monosilicide structure type