MnGe Research Articles

Crystallization and structural relaxation of Co 48Mn 20Ge 10B 10Si 12 amorphous alloy

Co–Mn–Ge metallic glass was produced by melt-spinning process. When annealed below its crystallization temperature, the alloy exhibited a dramatic increase in magnetization, which was attributed to the relaxation of the amorphous structure. The increased glass stability due to the relaxation by moderate annealing was well demonstrated as the amorphous alloy remained nearly amorphous during the second annealing step even though the annealing temperature was raised well above the crystallization temperature. It was concluded that a redistribution of Ge atoms and subsequent change in chemical short-range ordering may have been responsible for the observed relaxation phenomenon.

Magnetic and transport properties of MnGeP2 films grown on GaAs(001) by molecular beam epitaxy

Mn Ge P 2 films were grown on undoped GaAs(001) substrates by molecular beam epitaxy. X-ray diffraction analysis reveals a film peak at 66.21°, corresponding to a c-axis of 1.128nm for the chalcopyrite structure. Superconducting quantum interference device magnetic measurements show ferromagnetic order in the film with a transition temperature around 325K and hysteresis loop measurements yield with coercive fields of about 1600Oe and 210Oe at 250K and 300K, respectively. The transport measurements exhibit nonmetallic behavior with p-type carriers and a carrier density increasing with temperature. The anomalous Hall effect (AHE) is observed in the film indicating spin polarized carriers. At low temperatures, the anomalous Hall resistance has a negative sign and decreases in magnitude with increasing temperature, changing sign around 150K. It then increases with temperature, reaching a maximum around 250K.

Isothermal Section of the Ce—Mn—Ge Ternary System at 670 K.

AbstractFor Abstract see ChemInform Abstract in Full Text.

X-ray absorption spectroscopy in MnxGe1−x diluted magnetic semiconductor: Experiment and theory

Accurate first-principles calculations of soft x-ray absorption spectra are compared with experimental data obtained for the ion-implanted MnxGe1−x ferromagnetic semiconductor. The well-defined features in the spectra are recognized as a signature of homogeneous Mn dilution within the Ge host, as demonstrated by comparing the Mn spectra in diluted MnGe alloys with other competing Mn–Ge crystalline phases. Moreover, provided that an efficient Mn dilution is achieved, the nature of the semiconducting host is shown to affect only slightly the Mn absorption spectrum, as shown by the similarity of the present results with those for other magnetic semiconductors. Both these findings establish the relevance of ion-implantation in the dilute magnetic semiconductor framework, emphasizing its potential impact in device technology.

Initial stages of Mn adsorption on Ge(111)

The initial stages of growth of Mn on Ge(111) were studied with scanning tunneling microscopy, x-ray photoelectron spectroscopy, and first-principles density functional theory calculations. Mn atoms adsorb on the ${H}_{3}$ sites of the $\mathrm{Ge}(111)\text{\ensuremath{-}}c(2\ifmmode\times\else\texttimes\fi{}8)$ reconstruction, a process that is usually accompanied by a registry shift (along the $[1\overline{1}0]$ direction) of an adjacent Ge adatom row. Deposition of approximately one monolayer of Mn and subsequent annealing results in the formation of ${\mathrm{Mn}}_{5}{\mathrm{Ge}}_{3}$ islands. Epitaxial ${\mathrm{Mn}}_{5}{\mathrm{Ge}}_{3}$ films can be grown from a solid-state reaction between the Mn deposit and Ge substrate. The ${\mathrm{Mn}}_{5}{\mathrm{Ge}}_{3}$ films are ferromagnetic metals with a magnetic moment of $2.6\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{B}$ per Mn, as determined from the Mn $3s$ exchange splitting in XPS. Theoretical calculations of the adsorption sites, surface structures, and electronic structure all agree exceedingly well with the experimental observations.

Stabilization of substitutional Mn in silicon-based semiconductors

We systematically investigate, using ab initio density-functional theory calculations, the properties of interstitial and substitutional Mn in both Si and Ge, as well as in the ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$ alloy. We show that volume effects are not the main reason Mn prefers to be a subsitutional impurity in pure Ge, and chemical effects, therefore, play an important role. Using realistic models of ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$, we show that for $x\ensuremath{\gtrsim}0.16$ substitutional Mn in Ge-rich neighborhoods become more stable than interstitial Mn, which may allow the growth of Si-based diluted magnetic semiconductors.

Magnetic characteristics of epitaxial Ge(Mn,Fe) diluted films —a new room temperature magnetic semiconductor?

We prepare 100nm thick, epitaxial Ge100-(x+y)(Mnx,Fey) diluted films with Mn and Fe concentrations of several at% using a layer-by-layer deposition scheme at elevated temperature. We measure saturation magnetization mS versus temperature curves for a variety of (x,y) combinations and find for fixed temperatures a non-trivial dependence of mS on x and y. Within a certain window in the (x,y) parameter space Ge100-(x+y)(Mnx,Fey) exhibits a Curie temperature of 350K and mS≈ 10emu/cm2 at room temperature.

Structural and magnetic characterization of Mn 3IrGe and Mn 3Ir(Si 1−xGe x): experiments and theory

The structural and magnetic properties of a new ternary Ir–Mn–Ge phase, Mn 3IrGe, as well as the solid solution Mn 3Ir(Si 1− x Ge x ), 0 ⩽ x ⩽ 1 , have been investigated by means of X-ray and neutron powder diffraction, magnetization measurements and first principles calculations. The crystal structure is cubic, of the AlAu 4-type (an ordered form of the β-Mn structure), Z = 4 , space group P2 13, and the unit-cell dimension varies linearly with the silicon content. For all compositions, antiferromagnetic ordering is found below a critical temperature of about 225 K. The magnetic structure is noncollinear, as a result of frustrated magnetic interactions on a triangular network of Mn atoms, on which the moments rotate 120° around the triangle axes. The magnitude of the magnetic moment at 10 K is 3.39(4) μ B for Mn 3IrGe. The theoretical calculations reproduce with very good accuracy the magnitudes as well as the directions of the experimentally observed magnetic moments.

Isothermal section of the Ce–Mn–Ge ternary system at 670 K

The isothermal section of the phase diagram of the Ce–Mn–Ge ternary system was constructed at 670 K. Four ternary intermetallic compounds were found to exist. A critical assessment on the interaction of rare-earth elements (La–Lu) with manganese and germanium was made.

Magnetic behavior of (Al,Ge)65CuMn quaternary alloy quasicrystals

We report the results of field and temperature dependent magnetization measurements on (Al,Ge)65CuMn quasicrystalline samples with ∼22 and 24 at. % Mn. The Ge content is also kept ∼25 at. %. The data for these samples are then compared with the data taken on samples with low Ge content (∼10 and 0 at. %). Al40Ge25Cu10Mn25, a composition very close to one of the alloys studied here, is reported [Tsai et al., Jpn. J. Appl. Phys., 27, L2252 (1988)] in literature as a ferromagnetic, icosahedral QC with large TC. The detailed magnetic studies described here prove that the magnetism observed in these quaternary alloys is highly disordered. The two important observations made in our studies are (i) observation of short-range ferromagnetism in samples with high Ge and high Mn content, up to very high fields (H=5 T) and (ii) oscillatory magnetization (or existence of multiple minima in the M-T curves) observed for the same samples for H⩾1 kOe.

High-pressure X-ray diffraction study of UMn 2Ge 2

Uranium manganese germanide, UMn 2Ge 2, crystallizes in body-centered tetragonal ThCr 2Si 2 structure with space group I4/mmm, a=3.993 A ̊ and c=10.809 A ̊ under ambient conditions. Energy dispersive X-ray diffraction was used to study the compression behavior of UMn 2Ge 2 in a diamond anvil cell. The sample was studied up to static pressure of 26 GPa and a reversible structural phase transition was observed at a pressure of 1 6.1 GPa . Unit cell parameters were determined up to 12.4 GPa and the calculated cell volumes were found to be well reproduced by a Murnaghan equation of state with K 0=73.5 GPa and K′=11.4. The structure of the high-pressure phase above 16.0 GPa is quite complicated with very broad lines and could not be unambiguously determined with the available instrument resolution.

A magnetic study of TiNiSi-type GdMn 1− xTi xGe alloys

X-ray phase analysis and metallographic analysis were employed in investigations of the crystal structure of GdMn 1− x Ti x Ge ( x=0; 0.05; 0.1; 0.2) solid solutions. It is found that these new compounds crystallize in the orthorhombic TiNiSi-type structure. The magnetic properties of these solid solutions have been studied by magnetization and susceptibility measurements. All investigated compounds exhibit magnetic ordering of antiferromagnetic or ferromagnetic type. It was discovered that an increase of Ti content in the GdMn 1− x Ti x Ge samples leads to the appearance of ferromagnetic moment in these compounds and changes their magnetic ordering. The magnetic behavior of GdMn 1− x Ti x Ge is correlated with changes in Mn–Mn, Mn–Ge, and R–Mn distances.

Radiation-induced degradation of (Ph) 3GeMn(CO) 5 studied by EXAFS spectroscopy

The atomic structure degradation of (Ph) 3GeMn(CO) 5 resulting from radiolysis was studied by EXAFS spectroscopy. Mn and Ge K-edge EXAFS of (Ph) 3GeMn(CO) 5 were measured in the radiation dose range from 6.0×10 6 to 2.1×10 7 J/m 2. The following stages of structure degradation were found as functions of accumulated dose at radiation fluxes. At lower doses of 6×10 6–8×10 6 J/m 2 Mn–Ge bonds decompositions were detected: as a result the complex splits into fragments [(Ph) 3Ge] and [Mn(CO) n ]. At radiation dose 7.8×10 6 J/m 2 the [Mn(CO) n ] fragment partially loses CO-ligands to form Mn–Mn bonds, which are typical of Mn dimer. Further increase of the radiation dose up to 1.3×10 7 J/m 2 results in formation of Mn nanoparticles interacting with ligand environment. These Mn-nanoparticles are not changed at further increasing of radiation dose. The fragment [(Ph) 3Ge] remains unchanged up to 1.3×10 7 J/m 2. In the radiation dose range from 1.3×10 7 to 2.1×10 7 J/m 2, the [(Ph) 3Ge] fragment loses the Ph-ligands to form Ge–Ge bonds. The final products of radiolysis are inhomogeneous metal nanoparticles.

Correlation of Pr, Dy, and Tb addition with physical properties of InP layers prepared by liquid phase epitaxy

The characterisation of thick (>10 μm) InP layers prepared by liquid phase epitaxy with Pr, Dy and Tb rare earth element (REE) addition in the growth melt for applications in radiation detector structures is reported. A significant improvement of all the studied parameters with increasing concentration of REE up to critical value (0.25 wt%) was observed. The structural defect density was reduced by one order of magnitude and the residual impurity concentration by three and a half order of magnitude (< 1015 cm–3). The conductivity has been changed from n to p-type when REE exceeded certain concentration limit in the melt (0.15 wt% for Pr, 0.05 wt% for Tb and 0.03 wt% for Dy). The low-temperature photoluminescence (PL) spectra narrowed and the corresponding fine lines were resolved. Comparison of PL peaks of n and p- type conducting layers with the obtained electrical data leads to the conclusion that the dominant acceptor impurity for the n to p-type crossover is Ge for Pr addition and Mn for Tb and Dy addition.

EXAFS Study of Ph 3 GeMn(CO) 5 Structure Evolution on Exposure to X-Radiation

Ge K-edge and Mn K-edge EXAFS spectroscopy was used to study changes in the local environment of germanium and manganese atoms during radiolysis of the Ph3GeMn(CO)5 complex. On exposure to X-radiation, the metal complex undergoes a number of transformations depending on the radiant exposure (Φ). It was shown that at Φ = (6–8) × 106 J/m2, the initial metal complex decomposes into the [Ph3Ge] and [Mn(CO) n ] fragments with partial detachment of the CO groups from Mn atoms. When Φ = 1.3 × 107 J/m2, Mn atoms lose completely the CO groups to form finely dispersed metal nanoparticles, which interact with the surrounding atoms (carbon or nitrogen). With further increase in Φ, the local environment of the Mn atoms no longer changes. The Ge atoms remain coordinated to the Ph groups as Φ increases up to 2 × 107 J/m2, but starting with Φ = 1.6 × 107 J/m2, metal–metal bonds are formed; subsequently, the amount of this phase increases and when Φ = 2.6 × 108 J/m2, it becomes predominant. Since manganese and germanium atoms lose their ligands at different Φ values, one can conclude that germanium and manganese nanoparticles are the final products in the radiolysis of Ph3GeMn(CO)5.

Microstructure and mechanical properties of Fe–Mn–Ge Alloys

The microstructure and mechanical properties of Fe–Mn–Ge alloys have been investigated using optical microscopy, transmission electron microscopy, room temperature and high temperature X-ray diffraction (XRD) and tensile testing. It has been found that increasing Ge content in Fe–24Mn–Ge alloys considerably decrease the amount and width of ε martensite plates, which verifies the role of Ge in depressing the γ→ ε martensitic transformation in Fe–24Mn–Ge alloys. It has also been found that increasing Ge content decreases yield and tensile strength, and furthermore, increases the lattice parameter of austenite and the ductility in Fe–Mn–Ge alloys. High-temperature XRD shows that there is an anomalous expansion of the lattice parameter for the untransformed austenite below martensitic transformation temperature M s, compared with the linear relationship of lattice parameter vs. temperature between the Néel temperature T N, and the M s. Comparisons of the lattice parameter of austenite and ε martensite for several Fe–Mn–Ge and Fe–Mn–C alloys show that the alloy's contraction during the γ→ ε martensitic transformation mainly occurs at the direction being perpendicular to ε martensite plates. Therefore, it is believed that an internal stress, caused by the contraction of alloy being perpendicular to ε martensite plate, is responsible for the anomalous expansion of the untransformed austenite below the M s, and, the formation of the triangular grid microstructure of ε martensites. While the internal stress, which originated from the inhomogeneous dilation in the alloy may play important role in the thermally induced γ→ ε martensitic transformation.

X‐Ray Luminescence of Thin Oxide Films Containing Lead and Bismuth

We obtained thin films of the Bi4Ge3O12, Bi4Si2O12, PbWO4, and Bi2WO6 scintillators and investigated their luminescence properties on x‐ray excitation. We measured the x‐ray luminescence spectra and established the linear character for the dependence of the luminescence intensity on the power of the dose of x‐ray irradiation within the limits of up to 3·10−3 A/kg. We investigated the radiation stability of the films obtained. The possibility of their application for detecting ionizing radiation is investigated. The films based on Bi4Ge3O12 with an admixture of the Ge and Si or Mn activator of up to 1.5 mol.% are most suitable.

金属間化合物の粉末冶金プロセスと諸特性 Ｌ１２型構造を有する新規強磁性金属間化合物Ｍｎ３Ｇｅの合成

A new intermetallic compound, Mn3Ge, has been synthesized from the elemental components under high-pressure condition. The Rietveld analysis of the powder X-ray diffraction data revealed that the compound crystallizes into the cubic L12-type (Cu3Au-type) structure with the lattice parameter of a=0.38019 (3)nm. The result, as well as our former results on high-pressure synthesis of manganese germanides, suggests a remarkable change in binary Mn-Ge phase diagram under high-pressure condition. Mn3Ge exhibits metallic conduction and ferromagnetic behavior with a Curie temperature of 400K. The saturation magnetic moment is 0.87μB/Mn, indicating a possible itinerant electron ferromagnetism. The magnetic properties of Mn3Ge are discussed with isomorphous compounds and structurally related perovskite-type Mn3MC (M=A1, Ga, In, Zn, Sn) compounds.

Ferromagnetic phenomenon revealed in the chalcopyrite semiconductor CdGeP2:Mn

High concentration of Mn atoms has been successfully incorporated into the chalcopyrite type II–IV–V2 semiconductor CdGeP2 by solid-state reaction technique without causing any structural changes. Polycrystalline powder of the chalcopyrite-related material in Cd–Mn–Ge–P quaternary system has been additionally synthesized by sintering technology. Well-defined M–H hysteresis loops were observed at room temperature in CdGeP2:Mn single crystal and polycrystalline powder samples grown independently. The Curie temperature has been determined to be 320 K for single crystal phase CdxMn1−xGeP2 and 310 K for the polycrystalline powder. Magnetic force microscopy (MFM) observation clearly showed a stripe domain pattern on the Mn-diffused surface of CdGeP2 single crystal. The magneto-optical Kerr ellipticity spectrum of CdGeP2:Mn crystal showed a peak around 1.75 eV at T=300 K.

Doping effects from Fe and Ge for Mn in La1-xCaxMnO3(x = 0.15-0.6)

Effects from 4% Fe or Ge for Mn in La1-xCaxMnO3 (x = 0.15-0.6) arestudied experimentally. All the compounds exhibit orthorhombic structure,unaffected by the introduction of Fe and Ge. The magnetic ordering temperature(Tc) and, accordingly, the metal-insulator transition decrease systematicallydue to the presence of secondary ions at the Mn lattice. The doping effectsdepend on dopant and Ca content, and the typical reduction in Tc, compared tothe undoped counterparts, is ~60 K. Ge is more effective in suppressing themagnetic coupling for x⩽0.35, as indicated by the ~25 K lower Curietemperature in the Ge-doped compounds. When x exceeds 0.35, the Fe- andGe-doping effects reverse. The other striking observation of the presentstudy is the significant ferromagnetic enhancement below ~130 K, characterizedby a sharp jump of the magnetization under a field of 5 T, and the re-entranceof the charge ordering state below ~50 K in the Ge-doped La0.5Ca0.5MnO3. Thedifferent doping effects of Fe and Ge presumably originate from theirdifferent roles of charge carrier mobility. The magnetic coupling between Feand host Mn seems unimportant.