The influence of the incommensurately modulated structure on the physical properties of Fe1.35Ge (original) (raw)
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Applied Physics Letters, 2008
We have investigated electrical and magnetic properties of single-crystalline Fe 5 Si 3 nanowires. The nanowire ensemble shows ferromagnetic properties with a high T c of 380 K, small coercivity, and no remanence in zero field at room temperature. Such magnetic properties of the single-crystalline nanowires should give a chance to realize not only novel nanospintronic devices but also biomedical applications. Electrical transport measurements on single Fe 5 Si 3 nanowire device show metallic properties with low resistivity of 487 µ · Ω · cm. Fe 5 Si 3 nanowires are the first example of single-crystalline metallic ferromagnet with a T c higher than room temperature.
Tuneable structure and magnetic properties in Fe3−V Ge alloys
Journal of Alloys and Compounds, 2020
We report a detailed experimental and theoretical study of the effects of V substitution for Fe atom on the structural, magnetic, transport, electronic and mechanical properties of an off-stoichiometric Fe 3− V Ge intermetallic alloy series (0 ≤ ≤ 1). Single phase microstructures are observed for < 0.75, whereas higher V content alloys ≥ 0.75 are multi-phased. Vanadium substitution is observed to induce a diffusionless martensitic phase transformation from a Heusler-like L2 1 structure to hexagonal DO 19 structure, as corroborated by Differential Scanning Calorimetry results. The vanadium substitution is also found to decreases the grain size, inhibiting the grain growth by pinning the grain boundary migration. All the alloys in the series are found to be soft ferromagnets at 5 K with saturation magnetic moment and Curie temperature decreasing as V concentration increases. The low temperature saturation magnetic moment is in close agreement with the expected Slater-Pauling values for the L2 1 phases, while the hexagonal samples have markedly higher values of saturation moments. First-principle calculations agree with the experimental findings and reveal that V substitution energetically favours one of the Fe sites in Fe 3 Ge. The electrical resistivity measured over the temperature range from 5 K to 400 K shows negative temperature coefficient of resistivity at high temperatures with increasing the V concentration. Relatively high mechanical hardness values are also observed, with the values increasing with increasing V content. Vanadium substitution is found to play a central role in tuning the mechanical properties, stabilising the L2 1 structure, and shifting the martensitic transformation temperature to higher values from that of parent Fe 3 Ge.
Magnetic, thermal, and transport properties of single-crystalline U3Fe4Ge4
Journal of Alloys and Compounds, 2013
Magnetic, thermal, and transport properties of a U 3 Fe 4 Ge 4 single crystal have been studied. The compound crystallizes in the orthorhombic Gd 3 Cu 4 Ge 4 structure type. U 3 Fe 4 Ge 4 displays ferromagnetic order below the Curie temperature T C = 18 K. The magnetism originates from the uranium sublattice, as iron atoms have no ordered magnetic moments. U 3 Fe 4 Ge 4 exhibits a pronounced easy-axis anisotropy with the anisotropy field exceeding 60 T. The spontaneous magnetic moment is M s = 1.2 l B /f.u. at T = 2 K. Magnetic contribution to specific heat shows a gap excitation behavior with D = 4 meV, which can be related to the magnon gap due to the anisotropy. The Sommerfeld coefficient of the electronic specific heat is c = 57 mJ/(mol-U K 2) in the ordered state, whereas it is much higher (145 mJ/(mol-U K 2) if derived from the paramagnetic state. Electrical resistivity has very high values on the mX cm range.
Effects of Ge substitution on the thermoelectric properties and pseudogap characteristics of Fe2VGa
Journal of Physics: Condensed Matter, 2008
We report the effects of partial substitution of Ge onto the Ga sites of Fe 2 VGa by measuring electrical resistivity, Seebeck coefficient and thermal conductivity as a function of temperature. It is found that Ge substitution effectively dopes electrons to the system and thus causes a dramatic decrease in the electrical resistivity. The Seebeck coefficient changes sign from positive to negative upon replacing Ga by Ge, which is in good agreement with a simple band filling picture. In addition, the magnitude of the Seebeck coefficient gradually increases and attains a maximum value of 85 μV K −1 at around 120 K for Fe 2 VGa 0.9 Ge 0.1. Such a variation of Seebeck coefficient can be understood by means of rigid band-like shifting of the Fermi level across the pseudogap. The thermal conductivity is also reduced and a detailed analysis based on the Debye approximation indicates that the extrinsic disorder introduced by Ge substitution in Fe 2 VGa has a minor contribution to the point defect scattering. Other lattice imperfections, such as antisite disorder, may be the main source for the point defect scattering which shows no systematic variation with Ge concentration. While the thermoelectric performance improves with the partial substitution of Ge, the largest figure-of-merit (Z T) value among these presently investigated alloys is still an order of magnitude lower than the conventional thermoelectric materials.
Journal of Magnetism and Magnetic Materials, 1998
The relation between crystal structure, microstructure and magnetic structure in TbFe Ge is derived on the basis of neutron powder diffraction for samples annealed at 925, 800 (part I) and 650°C. All samples display a density modulation of only the guest subsystem (Tb/Tb* and Ge5/Ge5*) described by the wave vector q"(, , 0) of the orthohexagonal YCo Ge structure. The occupancy of the Tb site is 1 for the sample with ¹ "925°C and decreases to 0.830(6) for the sample with ¹ "650°C. At high temperatures (HT) ¹ (¹(¹ , (¹ , +450 K, ¹ "9.5 K) the Fe moments order with the wave vector q "(0 1 0) and have an antiferromagnetic collinear arrangement (#!#!))) along the x-axis. The Tb magnetic order sets in at ¹ "9.5 K and is associated with two wave vectors q "(0 1 0) (antiferromagnetic, AF) and q "(0 0 0) (ferromagnetic, F). The Tb F-component is parallel to x, while the Tb AF-component is confined to the (x 0 z)-plane. However, their relative amount depends strongly on the thermal history and this in turn influences the Fe ordering. The largest Tb F-component is observed for the sample with ¹ "925°C and it induces a reorientation of the Fe moments below ¹ which at 1.4 K are tilted away from the x-axis by an angle VW "25.0(6)°. The 1.4 K ordered moment values are 2.22(4) /Fe and 8.0(1) /Tb. The coupling within the Tb[1 0 0]-layers stacked along x is F. The canted ferrimagnetic structure has moments in general directions and comprises four sublattices, two Fe AF and two Tb ferrimagnetic. For sample with ¹ "650°C the Tb AF-component is dominant, leading to a braking of the F coupling within the Tb[1 0 0]-layers. The Fe moments preserve the HT arrangement below ¹. The 1.4 K ordered moment values are 2.29(6) /Fe, 9.5(2) /Tb (x"0) and 4.1(2) /Tb (x"0.5). The canted magnetic structure comprises six sublattices, two Fe AF and four Tb ferrimagnetic, all within the (x 0 z) plane. The change of the Tb atoms distribution and coherency of the guest subsystem (peak broadening) are coupled in two ways with the magnetic ordering. They change the total
Physical Review B, 2010
We have studied the growth and magnetic properties of thin Fe-Ge films synthesized ͑codeposited at room temperature and postannealed at 250°C͒ on Ge͑111͒ wafers versus stoichiometry. Morphology and crystal structure have been investigated in situ by means of scanning tunneling microscopy, low-energy electron diffraction, and x-ray photoelectron diffraction and ex situ with x-ray diffraction. The magnetic properties were characterized ex situ by conventional polar and longitudinal magneto-optical Kerr effect and transverse biased initial inverse susceptibility and torque measurements. It is found that the growth is epitaxial for Ge content up to ϳ48 at. % ͑ϳFe 1.1 Ge composition͒. In particular, the film is homogeneous and flat and adopts a crystalline structure of hexagonal symmetry derived from the B8 2 ͑Ni 2 In͒ structure over a wide stoichiometry range extending from Fe 2 Ge to Fe 1.1 Ge. The epitaxial orientation between the Ge substrate and the germanide layer is ͑0001͒Fe-Geʈ ͑111͒Ge with ͓1120͔Fe-Geʈ ͓110͔Ge. We found however that the surface periodicity and the out-of-plane lattice parameter c evolve within this stoichiometry range and two distinct stoichiometry regimes appear on both sides of a critical stoichiometry ͑ϳFe 1.5 Ge͒. Indeed, from Fe 2 Ge to Fe 1.5 Ge the surface periodicity is p͑2 ϫ 2͒ and c continuously decreases with Fe content, whereas from Fe 1.5 Ge to Fe 1.1 Ge the surface periodicity is ͑ ͱ 3 ϫ ͱ 3͒R30°and c remains constant. These features have been interpreted as a clear fingerprint of a minor transformation of the crystalline structure but without any change in symmetry. This structural order transformation is discussed in relation to previous results reported in the case of macroscopic single-crystal Fe-Ge ingots. On both sides of the wide ͓Fe 2 Ge, Fe 1.1 Ge͔ composition range the layer is no more homogeneous. More precisely, for higher Fe content the film contains both the above mentioned Ni 2 In-derived phase and a Fe-richer phase ͑probably bcc Fe͒ whereas for higher Ge content the layer is amorphous. Magnetic characterization showed in particular that the homogeneous Ni 2 In-derived epilayers are ferromagnetic with a Curie temperature that varies drastically with the stoichiometry, rising up to a high T C value of ϳ450 K for the Fe-rich Fe 1.9 Ge composition. Finally, whatever the stoichiometry, the magnetic easy axis of the homogeneous phase lies in the film plane and a small uniaxial anisotropy is superimposed on a sixfold order one that results from the hexagonal symmetry of the crystallographic structure.
Physical Review Letters, 2003
The phase diagram of FeSi1−xGex, obtained from magnetic, thermal and transport measurements on single crystals, shows a first-order transition from a correlated electron semiconductor to a ferromagnetic metal at a critical concentration, xc ≈ 0.25. The gap of the insulating phase strongly decreases with x. The specific heat γ coefficient appears to track the density of states of a Kondo insulator. The phase diagram is consistent with a correlation induced insulator-metal transition in conjunction with disorder on the Si/Ge ligand site.
Materials Research Bulletin, 1984
Crystal growth experiments were performed in the Fe203 -Ge02 system by chemical vapour transport. After determination of transport conditions by HCI or TeCI4, single crystals of the following compounds were prepared : a-Fe203 (hematite), Fe8Ge3018 (unknown structural type), Fe2Ge05 (kyanite-type) and GeO 2 (futile-type modification). Analyses of crystals by electron microprobe and neutron activation were used to check the stoichiometry and composition of the phases. Preliminary studies on crystals led to a monoclinic symmetry for FesGe30]8 (possible space group P 2/c or P c ) with a = 0.8754 r~, b = 0.5110 nm, c = 1.4280 m, and @ = 101.8 ° . The Fe8Ge3018 compound was found to display structural features similar to those of Fe2GeO 5 with the kyanlte-type.
A DFT study of the electronic and magnetic properties of Fe2MnSi1−xGex alloys
Journal of Magnetism and Magnetic Materials, 2012
We performed density functional theory (DFT) calculations to study the structural, electronic and magnetic properties of Fe 2 MnSi 1 À x Ge x alloys (x ¼ 0, 0.25, 0.50, 0.75, and 1.00). The lattice constant is found to increase linearly as a function of Ge concentration with a decrease in the formation energy. The total magnetic moment is found to be 3 m B for all alloys with the most contribution from Mn local magnetic moments. Iron atoms, however, exhibit much smaller spin moments about 10% of the bulk value. It seems that due to the proximity of Fe, magnetic moments have been induced on the sp atoms, which couple antiferromagnetically with Fe and Mn spin moments. Although, the band gap remains almost constant (0.5 eV), the spin-flip gap decreases as a function of x.
Room Temperature Ferromagnetic, Anisotropic, Germanium Rich FeGe(001) Alloys
Materials, 2013
Ferromagnetic Fe x Ge 1−x with x = 2%-9% are obtained by Fe deposition onto Ge(001) at high temperatures (500 °C). Low energy electron diffraction (LEED) investigation evidenced the preservation of the (1 × 1) surface structure of Ge(001) with Fe deposition. X-ray photoelectron spectroscopy (XPS) at Ge 3d and Fe 2p core levels evidenced strong Fe diffusion into the Ge substrate and formation of Ge-rich compounds, from FeGe 3 to approximately FeGe 2 , depending on the amount of Fe deposited. Room temperature magneto-optical Kerr effect (MOKE) evidenced ferromagnetic ordering at room temperature, with about 0.1 Bohr magnetons per Fe atom, and also a clear uniaxial magnetic anisotropy with the in-plane 110 easy magnetization axis. This compound is a good candidate for promising applications in the field of semiconductor spintronics.