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The availability of large high-quality single crystals is an important prerequisite for many studies in solid-state research. The optical floating-zone technique is an elegant method to grow such crystals, offering potential to prepare samples that may be hardly accessible with other techniques. As elaborated in this report, examples include single crystals with intentional compositional gradients, deliberate off-stoichiometry, or complex metallurgy. For the cubic chiral magnets Mn$_{1-x}$Fe$_{x}$Si and Fe$_{1-x}$Co$_{x}$Si, we prepared single crystals in which the composition was varied during growth from $x = 0 - 0.15$ and from $x = 0.1 - 0.3$, respectively. Such samples allowed us to efficiently study the evolution of the magnetic properties as a function of composition, as demonstrated by means of neutron scattering. For the archetypical chiral magnet MnSi and the itinerant antiferromagnet CrB$_{2}$, we grew single crystals with varying initial manganese (0.99 to 1.04) and boron (1.95 to 2.1) content. Measurements of the low-temperature properties addressed the correlation between magnetic transition temperature and sample quality. Furthermore, we prepared single crystals of the diborides ErB$_{2}$, MnB$_{2}$, and VB$_{2}$. In addition to high vapor pressures, these materials suffer from peritectic formation, potential decomposition, and high melting temperature, respectively., Comment: 16 pages, 13 figures

Silicon waste (SW), a byproduct from the photovoltaic industry, can be a prospective and environmentally friendly source for silicon in the field of thermoelectric (TE) materials. While thermoelectricity is not as sensitive toward impurities as other semiconductor applications, the impurities within the SW still impede the enhancement of the thermoelectric figure of merit, zT. Besides, the high thermal conductivity of silicon limits its applications as a TE material. In this work, we employ traditionally metallurgical methods in industry reducing the impurities in SW to an extremely low level in an environmentally friendly and economical way, and then the thermal conductivity of purified silicon is greatly reduced due to the implementation of multiscale phonon scattering without degrading the power factor seriously. Benefiting from these strategies, from 323 to 1123 K, for the sample made from purified silicon waste, the average zT, relevant for engineering application, is increased to 0.32, higher than that of the state-of-the-art n-type Ge-free bulk silicon materials made from commercially available silicon, but the total cost of our samples is negligible.

Although Mn-Ga alloys are discussed as novel permanent magnetic materials, there are several drawbacks, including the high price of Ga and the yet too small saturation magnetization to name a few. We used several guidelines to motivate the replacement of Ga by Sn to tackle these issues and explored the phase formation, structural and magnetic properties of a Mn 2.6 Ga 1− x Sn x alloy series. The structure of Sn-rich samples is dominated by the corresponding hexagonal and orthorhombic phases, while the structure of Ga-rich samples shows additional contributions from the tetragonal DO 22 structure. However, formation of the tetragonal phase happens only upon an appropriate annealing procedure. In contrast to the discussion in the literature, our experiments do not hint on the tetragonal DO 22 structure being metastable, but rather indicate the DO 22 structure being an equilibrium phase. In general, the experimentally found phase fractions impact on the magnetic properties and hard magnetic properties are downgraded very rapidly even if only a small amount of Ga is substituted by Sn. This indicates that the DO 22 phase found only in the Ga-rich samples is indeed the one which is most relevant for realization of high magnetic anisotropy.

Solid state single crystal growth (SSCG) is a crystal growth technique where crystals are grown from a polycrystalline matrix. Here, we present single crystals of the iron pnictide LaFeAsO grown via SSCG using NaAs as a liquid phase to aid crystallization. The size of the as-grown crystals are up to 2 × 3 × 0.4 mm 3 . Typical for this method, but very uncommon for crystals of the pnictide superconductors and especially for the oxypnictides, the crystals show pronounced facets caused by considerable growth in c direction. The crystals were characterized regarding their composition, structure, magnetic, and thermodynamic properties. This sets the stage for further measurements for which single crystals are crucial such as any c axis and reciprocal space dependent measurements.

The TSFZ growth of Nd-substituted LSCO (La1.81-xNdxSr0.19CuO4, x = 0 ÷ 0.4) single crystals has been explored for the first time. Optimal growth parameters have been determined: oxygen pressure 5.5–6.5 bar; CuO-poor solvent (66 mol.% CuO) and growth rate 0.6 mm/hour. As a result, high quality single crystals with composition La1.81-xSr0.19NdxCuO4 (x = 0, 0.2, 0.3, 0.4) have been successfully grown and characterized by optical polarized microscopy, x-ray diffraction and energy dispersive x-ray spectroscopy analysis. Substitution of La3+ with smaller Nd3+ ions leads to a gradual decrease of lattice parameters as well as of the superconducting transition temperature from 29.5 K for x = 0 to 14.6 K for x = 0.4.

Chemical and structural phase compositions of two single-crystalline samples prepared with different cooling rates from stoichiometric FeTe 0.6 Se 0.4 melts were studied. Both types of samples were investigated in a very comprehensive way using magnetic and electrical transport measurements combined with X-ray, neutron and electron backscatter diffraction. We show that slowly cooled samples are homogeneous on a microscopic scale with only a small excess of iron. Those slowly cooled samples do not exhibit bulk superconductivity down to 1.8 K. In contrast, fast-cooled samples are superconducting below about 14 K but are composed of several chemical phases: they consist of a matrix preserving the crystal structure of slow-cooled samples, and of core-shell structured dendritic inclusions (about 20–30 vol%). These have different crystal structures and chemical compositions and order magnetically at temperatures far above the superconducting transition temperature of the inhomogeneous samples. These structural and chemical inhomogeneities seem to play a vital role in the superconducting properties of this and similar iron-based systems as they lead to internal stress and act in a similar way as the application of the external pressure that reportedly increase the superconducting transition temperature in many iron pnictides and chalcogenides. We argue that a phase pure, homogeneous and stress-free FeTe 0.6 Se 0.4 is non-superconducting.

Single crystals of the double perovskite Sr2NiWO6 were synthesized via SrCl2 flux growth using high quality, phase-pure polycrystalline Sr2NiWO6 as precursor material. This high quality precursor enabled us to grow large and phase pure crystals with sizes up to 1 mm ×1 mm in the basal plane and octahedral morphology. We measured the temperature dependence of the magnetization along the c-axis and along the ab plane. The analysis of the data allows a precise determination of the effective magnetic moment and the Curie–Weiss temperature. Sr2NiWO6 orders antiferromagnetically at TN=54 K as revealed by magnetization and specific heat data.

The nonmagnetic compounds showing extremely large magnetoresistance are attracting a great deal of research interest due to their potential applications in the field of spintronics. ${\mathrm{PtBi}}_{2}$ is one of such interesting compounds showing large linear magnetoresistance (MR) in both the hexagonal and pyrite crystal structure. We use angle-resolved photoelectron spectroscopy and density functional theory calculations to understand the mechanism of liner MR observed in the layered ${\mathrm{PtBi}}_{2}$. Our results uncover linear dispersive surface Dirac states at the $\overline{\mathrm{\ensuremath{\Gamma}}}$ point, crossing the Fermi level with a node at a binding energy of $\ensuremath{\approx}900$ meV, in addition to the previously reported Dirac states at the $\overline{M}$ point in the same compound. We further notice from our dichroic measurements that these surface states show an asymmetric spectral intensity when measured with left and right circularly polarized light, hinting at a substantial spin polarization of the bands. Following these observations, we suggest that the linear dispersive Dirac states at the $\overline{\mathrm{\ensuremath{\Gamma}}}$ and $\overline{M}$ points are likely to play a crucial role for the linear field dependent magnetoresistance recorded in this compound.

Recently, the iridate double perovskite ${\mathrm{Sr}}_{2}{\mathrm{YIrO}}_{6}$ has attracted considerable attention due to the report of unexpected magnetism in this ${\mathrm{Ir}}^{5+}$ $(5{d}^{4})$ material, in which according to the ${J}_{\mathrm{eff}}$ model, a nonmagnetic ground state is expected. However, in recent works on polycrystalline samples of the series ${\mathrm{Ba}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{YIrO}}_{6}$ no indication of magnetic transitions have been found. We present a structural, magnetic, and thermodynamic characterization of ${\mathrm{Sr}}_{2}{\mathrm{YIrO}}_{6}$ single crystals, with emphasis on the temperature and magnetic field dependence of the specific heat. As determined by x-ray diffraction, the ${\mathrm{Sr}}_{2}{\mathrm{YIrO}}_{6}$ single crystals have a cubic structure, with space group $Fm\overline{3}m$. In agreement with the expected nonmagnetic ground state of ${\mathrm{Ir}}^{5+}$ $({5d}^{4})$ in ${\mathrm{Sr}}_{2}{\mathrm{YIrO}}_{6}$, no magnetic transition is observed down to 430 mK. Moreover, our results suggest that the low-temperature anomaly observed in the specific heat is not related to the onset of long-range magnetic order. Instead, it is identified as a Schottky anomaly caused by paramagnetic impurities present in the sample, of the order of $n\ensuremath{\sim}0.5(2)%$. These impurities lead to non-negligible spin correlations, which nonetheless, are not associated with long-range magnetic ordering.

Many Heusler compounds are predicted to be half-metallic ferromagnets and thus find extensive interest as materials for spintronic applications, an example of which is the Co2Cr1–xFexAl series. So far, bulk samples of that series, in particular, Cr-rich samples, do not verify those predictions, and various studies have yielded results that are fraught with anomalies. Thin films as well do not meet expectations, neither in magnetoresistance ratio nor in degree of spin polarization and magnetic moments. Polycrystalline samples of Co2CrAl, Co2FeAl, and Co2Cr0.6Fe0.4Al were found to be phase segregated, a hurdle easily tackled by using the optical floating zone (FZ) technique. Hence, in this work, we have carried out crystal growth of Co2Cr1–xFexAl Heusler compounds, as a step toward understanding the intrinsic material properties of this series. Our results demonstrate that, although the phase segregation is eliminated in the FZ grown samples, an unexpected phase transformation via spinodal decomposition tak...

A facile synthesis approach for the synthesis of ternary intermetallic nanocrystals was demonstrated exemplarily with the Heusler compound Co2FeGa. The method, involving prefabricated multiwalled carbon nanotubes which act as a template and protective shell, results in the formation of mainly spherical, chemically stable, and crystalline nanoparticles with a well-defined diameter distribution. As an example, for novel functionalities arising from downscaling a bulk material, we observe an enhancement of the coercive field of the Co2FeGa nanocrystals by a factor of ≈30. Our work can facilitate the exploration and eventually the tuning of physical properties of ternary and other intermetallic compounds at the nanoscale.

The floating-zone growth of massive intermetallic single crystals is very often unsuccessful due to unfavorable solid–liquid interface geometry and insufficient mixing of the melt which depends on the flow in the molten zone. A tailored magnetic two-phase stirrer system with radio frequency (RF) heating has been developed which enables the control of the melt flow by a significant change of the flow field. The magnetic system was used for the crystal growth of the Heusler compound Mn3Si due to their interesting properties such an itinerant antiferromagnetic and incommensurate spin-density wave state. The grown crystals were oriented and cut to samples with the crystallographic orientations (100) and (110) normal to a plane. Measurements of the temperature dependence of magnetization and specific heat are discussed in terms of contributions of other thermodynamic phases and phase transitions.

We report the structural, magnetic, and thermodynamic properties of the double perovskite compound ${\mathrm{La}}_{2}{\mathrm{CuIrO}}_{6}$ from x-ray, neutron diffraction, neutron depolarization, $\mathit{dc}$ magnetization, $\mathit{ac}$ susceptibility, specific heat, muon-spin-relaxation $(\ensuremath{\mu}\mathrm{SR})$, electron-spin-resonance (ESR) and nuclear magnetic resonance (NMR) measurements. Below $\ensuremath{\sim}113$ K, short-range spin-spin correlations occur within the ${\mathrm{Cu}}^{2+}$ sublattice. With decreasing temperature, the ${\mathrm{Ir}}^{4+}$ sublattice is progressively involved in the correlation process. Below $T=74$ K, the magnetic sublattices of Cu (spin $\mathit{s}=\frac{1}{2}$) and Ir (pseudospin $\mathit{j}=\frac{1}{2}$) in ${\mathrm{La}}_{2}{\mathrm{CuIrO}}_{6}$ are strongly coupled and exhibit an antiferromagnetic phase transition into a noncollinear magnetic structure accompanied by a small uncompensated transverse moment. A weak anomaly in $\mathit{ac}$ susceptibility as well as in the NMR and $\ensuremath{\mu}\mathrm{SR}$ spin lattice relaxation rates at 54 K is interpreted as a cooperative ordering of the transverse moments which is influenced by the strong spin-orbit coupled $5\mathit{d}$ ion ${\mathrm{Ir}}^{4+}$. We argue that the rich magnetic behavior observed in ${\mathrm{La}}_{2}{\mathrm{CuIrO}}_{6}$ is related to complex magnetic interactions between the strongly correlated spin-only $3\mathit{d}$ ions with the strongly spin-orbit coupled $5\mathit{d}$ transition ions where a combination of the spin-orbit coupling and the low symmetry of the crystal lattice plays a special role for the spin structure in the magnetically ordered state.

Nd2PdSi3 single crystals were grown by a vertical floating zone method with radiation heating at a zone traveling rate of 3 mm/h. The compound exhibits congruent melting behavior at a liquidus temperature of about 1790 °C. The actual crystal composition (35.3 ± 0.5) at.% Nd, (16.2 ± 0.5) at.% Pd, and (48.5 ± 0.5) at.% Si is slightly depleted in Pd and Si with respect to the nominal stoichiometry. Therefore, the gradual accumulation of these elements in the traveling zone led to a decrease of the operating temperature during the growth process. Single crystalline samples exhibit a large anisotropy due to the crystal electric field effect and order ferromagnetically below the Curie temperature TC = 15.1 K. The [001] orientation was identified as the magnetic easy axis at low temperatures. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Lu 2 PdSi 3 crystals have been grown by the floating zone method with optical heating. The congruently melting compound is a non-magnetic member of the class of R 2 PdSi 3 intermetallics (R: rare earths) with hexagonal AlB 2 -type crystallographic structure. The grown crystals are slightly Pd-depleted with respect to the nominal stoichiometry and contain a minor fraction of LuSi binary phase precipitates. Lu 2 PdSi 3 exhibits normal metallic behavior, but its electrical resistivity is highly anisotropic and deviates from the Bloch–Gruneisen law.

In this report the Co2 based Heusler compounds are discussed as potential materials for spin voltage generation. The compounds were synthesized by arcmelting and consequent annealing. Band structure calculations were performed and revealed the compounds to be half-metallic ferromagnets. Magnetometry was performed on the samples and the Curie temperatures and the magnetic moments were determined. The Seebeck coefficients were measured from low to ambient temperatures for all compounds. For selected compounds high temperature measurements up to 900 K were performed., accepted contribution o the Special Issue "Spin Caloritronics" of Solid State Communications

Materials with a $5{d}^{4}$ electronic configuration are generally considered to have a nonmagnetic ground state ($J=0$). Interestingly, ${\mathrm{Sr}}_{2}{\mathrm{YIrO}}_{6}$ (${\mathrm{Ir}}^{5+}$ having $5{d}^{4}$ electronic configuration) was recently reported to exhibit long-range magnetic order at low temperature and the distorted ${\mathrm{IrO}}_{6}$ octahedra were discussed to cause the magnetism in this material. Hence, a comparison of structurally distorted ${\mathrm{Sr}}_{2}{\mathrm{YIrO}}_{6}$ with cubic ${\mathrm{Ba}}_{2}{\mathrm{YIrO}}_{6}$ may shed light on the source of magnetism in such ${\mathrm{Ir}}^{5+}$ materials with $5{d}^{4}$ configuration. Besides, ${\mathrm{Ir}}^{5+}$ materials having $5{d}^{4}$ are also interesting in the context of recently predicted excitonic types of magnetism. Here we report a single-crystal-based analysis of the structural, magnetic, and thermodynamic properties of ${\mathrm{Ba}}_{2}{\mathrm{YIrO}}_{6}$. We observe that in ${\mathrm{Ba}}_{2}{\mathrm{YIrO}}_{6}$ for temperatures down to 0.4 K, long-range magnetic order is absent but at the same time correlated magnetic moments are present. We show that these moments are absent in fully relativistic ab initio band-structure calculations; hence, their origin is presently unclear.

The superconducting properties of ${\mathrm{LaFeAsO}}_{1\ensuremath{-}x}{\mathrm{F}}_{x}$ under conditions of optimal electron doping are investigated upon the application of external pressure up to $\ensuremath{\sim}23\text{ }\text{ }\mathrm{kbar}$. Measurements of muon-spin spectroscopy and dc magnetometry evidence a clear mutual independence between the critical temperature ${T}_{c}$ and the low-temperature saturation value for the ratio ${n}_{s}/{m}^{*}$ (superfluid density over effective band mass of Cooper pairs). Remarkably, a dramatic increase of $\ensuremath{\sim}30%$ is reported for ${n}_{s}/{m}^{*}$ at the maximum pressure value while ${T}_{c}$ is substantially unaffected in the whole accessed experimental window. We argue and demonstrate that the explanation for the observed results must take the effect of nonmagnetic impurities on multiband superconductivity into account. In particular, the unique possibility to modify the ratio between intraband and interband scattering rates by acting on structural parameters while keeping the amount of chemical disorder constant is a striking result of our proposed model.

We present a detailed experimental study of bulk and powder samples of the ferromagnetic Heusler shape-memory alloy ${\mathrm{Ni}}_{2}\mathrm{MnGa}$, including zero-field static and dynamic $^{55}\mathrm{Mn}$ NMR experiments, x-ray powder diffraction and magnetization experiments. The NMR spectra give direct access to the sequence of structural phase transitions in this compound, from the $\text{high}\ensuremath{-}T$ austenitic phase down to the $\text{low}\ensuremath{-}T$ martensitic phase. In addition, a detailed investigation of the so-called $rf\ensuremath{-}\text{enhancement}$ factor delivers the local magnetic stiffness and restoring fields for each separate structural environment, thus, differentiating signals coming from austenitic and martensitic components. In this way we can also resolve differences in the local spin moments of the two phases of the order of 0.08 Bohr magnetons, and reveal precursor phenomena of the martensitic transformation well inside the parent austenitic phase.

We present a comprehensive transport investigation of the itinerant antiferromagnet Mn3Si which undergoes a spin density wave (SDW) order below T_N~21.3K. The electrical resistivity, the Hall-, Seebeck and Nernst effects exhibit pronounced anomalies at the SDW transition, while the heat conductivity is phonon dominated and therefore is insensitive to the intrinsic electronic ordering in this compound. At temperatures higher than T_N our data provide strong evidence for a large fluctuation regime which extends up to ~200K in the resistivity, the Seebeck effect and the Nernst effect. From the comparison of our results with other prototype SDW materials, viz. LaFeAsO and Chromium, we conclude that many of the observed features are of generic character., Comment: 8 pages, 7 figures

We report the low-temperature properties of $^{11}$B-enriched single-crystal CrB$_{2}$ as prepared from high-purity Cr and B powder by a solid-state reaction and optical float zoning. The electrical resistivity, $\rho_{\rm xx}$, Hall effect, $\rho_{\rm xy}$, and specific heat, $C$, are characteristic of an exchange-enhanced Fermi liquid ground state, which develops a slightly anisotropic spin gap $\Delta \approx 220\,{\rm K}$ below $T_{\rm N}=88\,{\rm K}$. This observation is corroborated by the absence of a Curie dependence in the magnetization for $T\to0$ reported in the literature. Comparison of $C$ with $d\rho_{\rm xx}/dT$, where we infer lattice contributions from measurements of VB$_2$, reveals strong antiferromagnetic spin fluctuations with a characteristic spin fluctuation temperature $T_{\rm sf}\approx 257\,{\rm K}$ in the paramagnetic state, followed by a pronounced second-order mean-field transition at $T_{\rm N}$, and unusual excitations around $\approx T_{\rm N}/2$. The pronounced anisotropy of $\rho_{\rm xx}$ above $T_{\rm N}$ is characteristic of an easy-plane anisotropy of the spin fluctuations consistent with the magnetization. The ratio of the Curie-Weiss to the N$\acute{\rm{e}}$el temperatures, $f=-\Theta_{\rm CW}/T_{\rm N}\approx 8.5$, inferred from the magnetization, implies strong geometric frustration. All physical properties are remarkably invariant under applied magnetic fields up to $14\,\,{\rm T}$, the highest field studied. In contrast to earlier suggestions of local-moment magnetism our study identifies CrB$_{2}$ as a weak itinerant antiferromagnet par excellence with strong geometric frustration., Comment: 15 pages, 9 figures

Among the large class of Heusler compounds, Co2CrAl is predicted to be 100 % spin polarized and is hence, a potential candidate for application in spintronics. So far, the predicted properties have not been experimentally realized which may be attributed to the phase segregated nature of samples. This phase segregation is avoided using floating zone growth. However, the grown sample was found to have undergone phase transformation via spinodal decomposition at low temperatures. In the present work, thermal annealing has been done on the spinodally decomposed samples and its effect on microstructure, crystallographic structure and magnetic properties has been studied. Annealing experiments were done and analyzed in order to understand the extent of the solid state miscibility gap. With regards to the phase diagram, the two-phase regime was found to extend till 1000 {\deg}C. Even at 1250 {\deg}C, we are still inside the immiscibility region. The thermodynamic miscibility gap was thus found to exist until high temperatures and alternate routes might be required to obtain a single phase sample with the desired high spin polarization and Curie temperature in the Co-Cr-Al system., Comment: 10 pages, 5 figures, 24 references, Proceedings of 17th International Conference on Crystal Growth and Epitaxy (ICCGE-17)

We report the angular dependence of three distinct de Haas-van Alphen (dHvA) frequencies of the torque magnetization in the itinerant antiferromagnet CrB2 at temperatures down to 0.3K and magnetic fields up to 14T. Comparison with the calculated Fermi surface of nonmagnetic CrB2 suggests that two of the observed dHvA oscillations arise from electron-like Fermi surface sheets formed by bands with strong B-px,y character which should be rather insensitive to exchange splitting. The measured effective masses of these Fermi surface sheets display strong enhancements of up to a factor of two over the calculated band masses which we attribute to electron-phonon coupling and electronic correlations. For the temperature and field range studied, we do not observe signatures reminiscent of the heavy d-electron bands expected for antiferromagnetic CrB2. In view that the B-p bands are at the heart of conventional high-temperature superconductivity in the isostructural MgB2, we consider possible implications of our findings for nonmagnetic CrB2 and an interplay of itinerant antiferromagnetism with superconductivity., 8 pages, 4 figures

LiMn 0.95 Ni 0.05 PO 4 single crystals have been grown for the first time by the travelling-solvent floating-zone method at low argon pressure. The grown sample exhibits large single crystalline grains as revealed by means of polarization microscopy, X-ray Laue back scattering, and single-crystal X-ray diffraction. The composition of the crystal was determined by Energy-dispersive X-ray (EDX) spectroscopy. LiMn 0.95 Ni 0.05 PO 4 orders in an orthorhombic olivine-like structure as expected and phase purity was confirmed by powder X-ray diffraction. An oriented cuboid with size of 2.4×2.5×2.7 mm 3 along a , b , and c crystalline directions, respectively, was used for anisotropic magnetic measurements.

We present properties of single crystals of the iron pnictide superconductor RbFe2As2 grown using a self-flux method. A bulk superconducting transition at Tc ∼2.6 K was consistently observed in resistivity, magnetic susceptibility, and specific heat measurements. While the resistivity behaves like a conventional metal at low T, the magnetic susceptibility shows an unusual broad maximum around 80 K in the normal state. A large Sommerfeld coefficient, γ0=127mJ/mol K2, was observed seemingly a common feature of heavily hole-doped “122” compounds. In the superconducting state, we analyzed our specific heat data based on the s- and d-wave two-gap models. The presence of the small gap with 2Δ1(0)/kBTc

The quaternary Heusler compound ${\text{Co}}_{2}{\text{Mn}}_{1\ensuremath{-}x}{\text{Ti}}_{x}\text{Sn}$ with $x=0$, 0.2, 0.4, 0.5, 0.6, 0.8, and 1 shows a phase separation into the two Heusler compounds, ${\text{Co}}_{2}\text{MnSn}$ and ${\text{Co}}_{2}\text{TiSn}$. Only at the edges of the composition range a slight admixture of Mn and Ti to the respective other phase is observed. This phase separation leads to a distinct microstructure which can be altered by the composition of the material. Pronounced changes in the magnetic and electronic properties take place with varying composition. Two magnetic transitions occur which indicate different Curie temperatures for both phases. The reduction in the thermal lattice conductivity is of particular interest for an optimization of Heusler compounds for thermoelectric applications. In the field of spintronics the use of superlattices composed of ${\text{Co}}_{2}\text{MnSn}$ and ${\text{Co}}_{2}\text{TiSn}$ without any interlayer diffusion is suggested.

Co2Mn1-xFexSi Heusler alloys crystallize in the L21 structure. This structure type requires random distribution of Mn and Fe in case of the mixed alloys. The spin echo nuclear magnetic resonance (NMR) technique probes the direct local environments of the active atoms and is thus able to resolve next neighboring shells providing a unique tool to verify the random distribution of Mn and Fe in Co2Mn1-xFexSi. Exemplarily, the half-metallic quaternary Heusler alloy Co2Mn0.5Fe0.5Si was investigated by means of NMR. The 55Mn NMR measurements unambiguously demonstrate the random distribution of Mn and Fe on the 4b Wyckoff position in Co2Mn0.5Fe0.5Si.

Nowadays, a wealth of information on ultrafast magnetization dynamics of thin ferromagnetic films exists in the literature. Information is, however, scarce on bulk single crystals, which may be especially important for the case of multi-sublattice systems. In Heusler compounds, representing prominent examples for such multi-sublattice systems, off-stoichiometry and degree of order can significantly change the magnetic properties of thin films, while bulk single crystals may be generally produced with a much more well-defined stoichiometry and a higher degree of ordering. A careful characterization of the local structure of thin films versus bulk single crystals combined with ultrafast demagnetization studies can, thus, help to understand the impact of stoichiometry and order on ultrafast spin dynamics.Here, we present a comparative study of the structural ordering and magnetization dynamics for thin films and bulk single crystals of the family of Heusler alloys with composition Co2Fe1 − xMnxSi. The local ordering is studied by 59Co nuclear magnetic resonance (NMR) spectroscopy, while the time-resolved magneto-optical Kerr effect gives access to the ultrafast magnetization dynamics. In the NMR studies we find significant differences between bulk single crystals and thin films, both regarding local ordering and stoichiometry. The ultrafast magnetization dynamics, on the other hand, turns out to be mostly unaffected by the observed structural differences, especially on the time scale of some hundreds of femtoseconds. These results confirm hole-mediated spin-flip processes as the main mechanism for ultrafast demagnetization and the robustness of this demagnetization channel against defect states in the minority band gap as well as against the energetic position of the band gap with respect to the Fermi energy. The very small differences observed in the magnetization dynamics on the picosecond time-scale, on the other hand, can be explained by considering the differences in the electronic structure at the Fermi energy and in the heat diffusion of thin films and bulk crystals.

Co2FeAl0.5Si0.5 films with a surface roughness of 0.12 nm have been grown epitaxially on lattice-matched MgAl2O4 (001) substrates by off-axis sputtering. X-ray diffraction shows pronounced Laue oscillations, rocking curves as narrow as 0.0043°, and clear Co2FeAl0.5Si0.5 (111) peaks indicating L21 ordering. Magnetic characterizations show a clear magnetocrystalline anisotropy comprising cubic and epitaxy-induced uniaxial terms. Nuclear magnetic resonance measurements reveal L21 order of 81% in the Co2FeAl0.5Si0.5 films. Magnetotransport measurements show a distinct separation of anisotropic magnetoresistance and ordinary magnetoresistance. These results demonstrate the state-of-the-art crystalline quality and magnetic uniformity of the Co2FeAl0.5Si0.5 films.

Lu2PdSi3 represents a non-magnetic member of the class of R2PdSi3 intermetallic compounds (R = rare earths) with hexagonal AlB2-type crystallographic structure. The electrical resistivity of single crystalline Lu2PdSi3 is highly anisotropic and reflects metallic behaviour. Its temperature dependence follows the Bloch–Gruneisen law for c-axis orientation [001]. For [100] orientation in the perpendicular plane the observed deviation from the Bloch–Gruneisen law can be explained by the Ioffe–Regel criterion. The relatively low Debye temperature ΘD of the order of 200 K fairly well agrees with that derived from specific heat data of Lu2PdSi3. Notably, Lu2PdSi3 allows extracting the magnetic entropy contribution of isostructural R2PdSi3 compounds.

The thermoelectric properties of a Heusler compound with NiZr0.5Hf0.5Sn composition were studied. A comparison of the properties of a single crystal and a polycrystal was carried out by measurements of the electrical conductivity, Seebeck coefficient, and thermal conductivity. The transport properties are directly compared to the valence band electronic structure measured by photoelectron spectroscopy. The single crystal shows a higher figure of merit (ZT = 0.1) at room temperature which originates from the high electrical conductivity that is mediated by “in-gap” states observed by photoemission spectroscopy.

Mn2NiGa is reported to be a shape memory material with a martensite–austenite phase transition. Temperature dependent measurements of the transport and magnetic properties reveal the martensitic transition close to room temperature with a thermal hysteresis of about 27 K. The electronic structure of the valence band in both phases was studied by hard x-ray photoelectron spectroscopy. The results clearly indicate that strong changes in the electronic structure appear at the phase transition.

Co2FeSi is predicted to be a half-metallic ferromagnet with an extraordinary high magnetic moment and Curie temperature. However, a low tunnel magneto-resistance ratio, a lower spin polarization and a lower magnetic moment were experimentally observed in thin film samples. Consequently, thin Co2FeSi films of different groups were studied using spin-echo nuclear magnetic resonance (NMR). NMR probes the local hyperfine fields of the active atoms, which strongly depend on the local environment. NMR is thus able to reveal the next neighbouring shells of the Co-59 nuclei in the Co2FeSi thin films. As expected, our NMR study shows the main resonance line corresponding to Co-59 nuclei in the L2(1) environment but also additional resonance lines at the high frequency site of the main line with a spacing between adjacent resonance lines of 32 MHz. The additional resonance lines correspond to Co-59 with more Fe next neighbours than expected for the L2(1) type ordering, which is interpreted as the formation of an off-stoichiometric film yielded by sputtering from a stoichiometric target. The analysis of the NMR data and a comparison with off-stoichiometric bulk samples reveals the composition of the thin films to be about Co2Fe(Si0.92Fe0.08). This off-stoichiometry might explain the observed deviations from the expected behaviour.

Recent spin echo nuclear magnetic resonance (NMR) revealed that the half-metallic Co2Mn1-xFexSi Heusler alloys exhibit the L21 structure with random distribution of Mn and Fe on the 4b Wyckoff position. This random distribution is most prominent in the third coordination shell of the 55Mn nuclei, as this shell is the first magnetically active shell, leading to a line splitting in the 55Mn NMR spectra. A comparison, as presented in this paper, of all 55Mn NMR satellite lines shows that the resonance frequencies corresponding to the same number of Fe atoms in the third shell of 55Mn shift to slightly different resonance frequencies with increasing overall Fe content x. This shift is related to the constructive contribution of higher shells to the hyperfine field. These higher shells affect also the satellite linewidth, leading to a parabolic behavior with increasing Fe concentration x. This parabolic behavior is modified by the frequency spacing related to the replacement of Mn by Fe.