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Two Heusler compounds NiRh2Sb and CuRh2Sb were synthesized for the first time and their crystal structures were determined by combined X-ray diffraction and high-resolution electron microscopy. Two synthesis routes were applied: a one-pot polyol reduction of metal cations at 280–290 °C under microwave radiation yielded nanocrystalline particles of 3–6 nm, whereas intergrown microcrystalline samples were obtained by conventional high-temperature synthesis at 700 °C starting from the elements. NiRh2Sb is an orthorhombic Heusler compound that crystallizes in space group Cmcm with lattice parameters a = 6.9188(1) Å, b = 5.7917(1) Å and c = 5.7374(1) Å. CuRh2Sb is dimorphic; depending on the synthesis conditions, it either adopts the cubic space group Fm3¯m with a lattice parameter of a = 6.1235(1) Å, or the tetragonal space group I4/mmm with lattice parameters a = 4.1859(1) Å and c = 6.6375(1) Å. The transition between the cubic and tetragonal structures of CuRh2Sb is attributed to a reversible band Jahn–Teller distortion as suggested by density functional theory-based calculations. Electrical resistivities evidence metallic behavior for both compounds in accordance with the computed band structures and the density-of-states. Both compounds are Pauli paramagnetic and show no magnetic ordering between room temperature and 2 K. The electrocatalytic performances of the nano-scale intermetallics were tested with the electrolysis of water, and both were found to greatly reduce the overpotential of both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) with a large electrochemically active surface area. [ABSTRACT FROM AUTHOR]

Elastic constants and their derived properties of various cubic Heusler compounds were calculated using the first-principles density functional theory. To begin with, Cu 2 MnAl is used as a case study to explain the interpretation of the basic quantities and compare them with experiments. The main part of the work focuses on Co 2 -based compounds that are Co 2 Mn M with the main group elements M = Al , Ga, In, Si, Ge, Sn, Pb, Sb, Bi, and Co 2 T M with the main group elements Al or Si, and the 3 d transition metals T = Sc , Ti, V, Cr, Mn, and Fe. It is found that many properties of Heusler compounds correlate to the mass or nuclear charge Z of the main group element. Additional representation and compact simplification of the elastic data is useful to investigate and compare their influence on crystal stability and physical properties. Here, Blackman's and Every's diagrams are used to compare the elastic properties of the materials, whereas Pugh's and Poisson's ratios are used to analyze the relationship between interatomic bonding and physical properties. It is found that Pugh's criterion on brittleness needs to be revised whereas Christensen's criterion describes the ductile–brittle transition of Heusler compounds very well. The calculated elastic properties give hint on a metallic bonding with an intermediate brittleness for the studied Heusler compounds. The universal anisotropy of the stable compounds has values in the range of 0.57 < A U < 2.73. The compounds with higher A U values are found close to the middle of the transition metal series. In particular, Co 2 ScAl with A U = 0.01 is predicted to be an isotropic material that comes closest to an ideal Cauchy solid as compared to the remaining Co 2 -based compounds. Apart from the elastic constants and moduli, the sound velocities, Debye temperatures, and hardness are predicted and discussed for the studied systems. The calculated slowness surfaces for sound waves reflect the degree of anisotropy of the compounds. [ABSTRACT FROM AUTHOR]

Chirality depends on particular symmetries. For crystal structures it describes the absence of mirror planes and inversion centers, and in addition to translations, only rotations are allowed as symmetry elements. However, chiral space groups have additional restrictions on the allowed screw rotations as a symmetry element, because they always appear in enantiomorphous pairs. This study classifies and distinguishes the chiral structures and space groups. Chirality is quantified using Hausdorff distances and continuous chirality measures and selected crystal structures are reported. Chirality is discussed for bulk solids and their surfaces. Moreover, the band structure, and thus, the density of states, is found to be affected by the same crystal parameters as chirality. However, it is independent of handedness. The Berry curvature, as a topological measure of the electronic structure, depends on the handedness but is not proof of chirality because it responds to the inversion of a structure. For molecules, optical circular dichroism is one of the most important measures for chirality. Thus, it is proposed in this study that the circular dichroism in the angular distribution of photoelectrons in high symmetry configurations can be used to distinguish the handedness of chiral solids and their surfaces. [ABSTRACT FROM AUTHOR]

The present work reports on the calculated electronic and magnetic structure of the binary Co-Ga system at high Co content. β -CoGa adopts a simple cubic CsCl type structure. Well-ordered CoGa does not exhibit collective magnetism but is a paramagnetic, metallic compound. Neither Co nor Ga deficiency induces magnetic order; however, ferromagnetism is observed for Co-Ga anti-site disorder. The magnetic moment per cell increases by up to approximately 1.2 μ B in the completely disordered body-centered cubic structure. With increasing Co content, Co 1 + x Ga 1 − x maintains the CsCl type structure and becomes ferromagnetic. Most importantly, a discontinuity of the magnetic order with composition is observed at about 10% excess Co, where a change from a low magnetic moment state to a high moment state is observed. This is accompanied by a change in the electronic structure and transport properties. The discontinuity is forced by the increasing exchange splitting related to the localized moment of the additional Co atoms that replace Ga. Subsequently, the magnetic moment increases continuously up to 2.5 μ B for x = 0.6 . For x ≳ 0.6 , the structure changes to a face-centered cubic structure with random site occupation and the magnetic moment further increases. Above the magnetic discontinuity, the Curie temperature increases linearly with the Co content from the onset of ferromagnetism, until it reaches its maximum in pure Co. [ABSTRACT FROM AUTHOR]

Summary With more than 1000 known members, Heusler materials form a large group of intermetallic compounds. Despite their relatively simple cubic crystal structure, they exhibit an enormous variety of physical effects. The reason is not only their large number but also the possibility to tune them by substitution and heat treatment. Moreover, many of the properties of a Heusler compound, such as semiconductivity or the magnetic moment, can be predicted by simply counting the valence electrons. While the application as thermoelectrics and in spintronics mainly been explored in the past decades, the topological properties of Heusler compounds have recently attracted a lot of interest. [ABSTRACT FROM AUTHOR]

Permanent magnets are applied in many large‐scale and emerging applications and are crucial components in numerous established and newly evolving technologies. Rare‐earth magnets exhibit excellent hard magnetic properties; however, their applications are limited by the price and supply risk of the strategic rare‐earth elements. Therefore, there is an increasing demand for inexpensive magnets without strategic elements. Here, the authors report the intrinsic highly‐anisotropic magnetic properties of Co and Si co‐doped single crystals (Fe1−yCoy)2P1−xSix (y ≈ 0.09). Co increases Curie temperature TC; Si doping decreases magnetocrystalline anisotropy K1 and also increases TC significantly because of the enhanced interlayer interaction. The maximum room temperature magnetocrystalline anisotropy K1 = 1.09 MJ m−3 is achieved for x = 0.22, with saturation magnetization µ0Ms = 0.96 T and TC = 506 K. The theoretical maximum energy product is one of the largest for any magnet without a rare earth or Pt. Besides its promising intrinsic magnetic properties and absence of any strategic elements, other advantages are phase stability at high temperatures and excellent corrosion resistance, which make this material most promising for permanent magnetic development that will have a positive influence in industry and daily life. [ABSTRACT FROM AUTHOR]

The interplay between topology and magnetism has recently sparked the frontier studies of magnetic topological materials that exhibit intriguing anomalous Hall and Nernst effects owning to the large intrinsic Berry curvature (BC). To better understand the anomalous quantum transport properties of these materials and their implications for future applications such as electronic and thermoelectric devices, it is crucial to discover more novel material platforms for performing anomalous transverse transport studies. Here, it is experimentally demonstrated that low‐cost Fe‐based Heusler compounds exhibit large anomalous Hall and Nernst effects. An anomalous Hall conductivity of 250–750 S cm−1 and Nernst thermopower of above 2 µV K−1 are observed near room temperature. The positive effect of anti‐site disorder on the anomalous Hall transport is revealed. Considering the very high Curie temperature (nearly 1000 K), larger Nernst thermopowers at high temperatures are expected owing to the existing magnetic order and the intrinsic BC. This work provides a background for developing low‐cost Fe‐based Heusler compounds as a new material platform for anomalous transport studies and applications, in particular, near and above room temperature. [ABSTRACT FROM AUTHOR]

The tetragonal Mn2RhSn Heusler compound shows better lattice match with MgO than do Mn3-xGa and tetragonal Mn3-xCoxGa Heusler compounds and hence is better suited for spin transfer torque applications. Beside the improved lattice match, this compound shows a low saturation magnetic moment reduces the current to switch which makes it more relevant for application in spin transfer torque devices. This compound shows a low Curie temperature; introducing Co into this system and increasing the Rh content leads to an increase in the Curie temperature. Doping with Co retains the tetragonal structure, with improved lattice match with MgO and low magnetic moment, intact up to x = 0.6, although doping with Rh changes the structure from tetragonal to cubic. [ABSTRACT FROM AUTHOR]

Heusler nanocrystals, i.e., Heusler compounds with dimensions in nanometer range are promising materials for next-generation spin-related devices. Recently, we have developed a chemical approach to prepare L21 ordered Heusler nanoparticles and characterized their size-related structure and magnetic properties. In this work, effect of precursor composition is investigated in terms of their importance in controlling the phase structure of Co2FeGa nanoparticles. The formation of the L21 ordered Co2FeGa phase is evidenced by combining X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopy and Mössbauer spectroscopy measurements. From XRD, precursor compositions of low Co and high Fe are associated with decreasing amounts and even disappearance of fcc Co and fcc Fe impurities. We also find that, even though the XRD data indicate only pure Co2FeGa phase in sample with excess Fe, EXAFS and Mössbauer spectroscopy data unambiguously reveal the co-existence of bcc Fe with Co2FeGa main phase. [ABSTRACT FROM AUTHOR]

The Berry phase understanding of electronic properties has attracted special interest in condensed matter physics, leading to phenomena such as the anomalous Hall effect and the topological Hall effect. A non-vanishing Berry phase, induced in momentum space by the band structure or in real space by a non-coplanar spin structure, is the origin of both effects. Here, we report a sign conversion of the anomalous Hall effect and a large topological Hall effect in (Cr0.9B0.1)Te single crystals. The spin reorientation from an easy-axis structure at high temperature to an easy-cone structure below 140 K leads to conversion of the Berry curvature, which influences both, anomalous and topological, Hall effects in the presence of an applied magnetic field and current. We compare and summarize the topological Hall effect in four categories with different mechanisms and have a discussion into the possible artificial fake effect of the topological Hall effect in polycrystalline samples, which provides a deep understanding of the relation between the spin structure and Hall properties. [ABSTRACT FROM AUTHOR]

Although stoichiometric CrTe is difficult to synthesize because of the appearance of Cr vacancies, ferromagnetic Cr1−x Te compounds have attracted increasing attention. This work investigates single crystalline (Cr0.9 B0.1)Te with the Cr vacancies filled by B to stabilize the hexagonal crystal structure and shift the Fermi energy. The structural and magnetic properties have been characterized by experimental measurements and ab initio calculations. A collinear spin structure with an easy axis along c is observed at high temperature, whereas the magnetic moments localized at the Cr atoms gradually tilt away from the c-axis below 140 K. A maximum tilt angle of 30 ° is observed at a temperature of 2 K. [ABSTRACT FROM AUTHOR]

The quaternary LiMgPdSb-type CoFeMnSi are examined. The analysis of the measured XRD pattern and magnetization curve has shown that the CoFeMnSi compound is crystallized in the structure where half metallicity has occurred.

The studies have shown that Fe substituted Co[Ti.sub.1-x][Fe.sub.x]Sb is a new diluted semiconductor with a high Curie temperature of above 770 K. The small lattice mismatch among each other has made CoTiSb and the Fe doped Co[Ti.sub.1-x][Fe.sub.x]Sb very interesting for spin-light-emitting diodes or other spin injection devices.

The spin nuclear magnetic resonance (NMR) method is used for examining the next neighboring and higher shells of [Co.sub.2][Mn.sub.1-x][Fe.sub.x]Si Heusler alloys. The comparison of all [super 55]Mn NMR satellite lines have shown that the resonance frequencies corresponding to the same number of Fe atoms in the third shell of [super 55]Mn has shifted to slightly different resonance frequencies with increasing overall Fe content x.

Magnetic measurements are used for investigating the prediction of half-metallic ferromagnetism in [Rb.sub.4][O.sub.6]. These measurements have not confirmed the predicted magnetic state, thus concluding that the mixed oxide does not show the predicted half-metallicity.

A demonstration of how the Slater-Pauling rule can be applied to guide in the search of Heusler compounds that exhibit half-metallic ferromagnetism is provided. It is found that the [Co.sub.2] based compounds exhibit a seemingly linear dependence of the Curie temperature on the magnetic moment.

The Heusler compound [Co.sub.2]FeSi exhibits the highest magnetic moment as well as the highest Curie temperature among Heusler compounds. Study is conducted to show how to estimate the lower temperature limit of the magnetic-phase transition for materials with very high Curie temperatures by means of differential scanning calorimetry.

The ternary silicide system Fe-Mn-Si exhibits several complex magnetic phases and the chemical similarity of Fe and Mn enables these two elements to be mutually substituted over a wide compositional range. Because this substitution results in chemical disorder and often causes competing magnetic exchange interactions, frustrated spin glass ordering is expected to occur for some Fe-Mn-Si phases. However, the observation of a spin glass state within these alloys has been elusive to date. This paper reports magnetization and ac susceptibility measurements on Mn48Fe34Si18. The compound crystallizes in a Mn3IrSi-type structure, which is closely related to that of β-Mn. Typical spin glass behavior is observed at low temperatures. This comprises a bifurcation of field-cooled and zero-field-cooled magnetization, a displacement of the field-cooled hysteresis loop, magnetic relaxation, a memory effect, and a sharp, frequency-dependent cusp in the ac susceptibility at the freezing temperature. Mn48Fe34Si18 is demonstrated to be a canonical spin glass. [ABSTRACT FROM AUTHOR]

We report the synthesis, crystal structure, and basic physical properties of Ag8PtO6, which represents the first silver platinum ternary oxide. The crystalline compound was obtained from appropriate mixtures of the binary constituents under alkaline conditions at high oxygen pressure, while applying relatively mild thermal conditions (573 K). Ag8PtO6 crystallizes in a new crystal structure in the triclinic system (P1̅). The structure consists of slightly distorted, discrete PtO6 octahedra, which are linked via O–Ag–O dumbbells to form a three dimensional framework. It is a diamagnetic semiconductor with a band gap of 0.9 eV. DFT based calculations confirm an electronic ground state that corresponds to a 5d6 6s0 configuration of the Pt atoms, in accordance with the observed diamagnetism. [ABSTRACT FROM AUTHOR]

A good field to develop new materials with half metallicity is the quaternary Heusler alloys. The preferred route is to combine the compounds that have been already grown in Heusler structure. As a typical example, the quaternary LiMgPdSb-type CoFeMnSi have been investigated in detail. For the quaternary LiMgPdSb-type compounds, three nonequivalent structures exist. From the calculated density of state (DOS) results, it can be seen that one superstructure shows half metallicity. The second superstructure has a pseudogap at the Fermi level. The third superstructure shows metallic behavior. Based on the analysis of the measured XRD pattern and magnetization curve, we can deduce that the CoFeMnSi compound is crystallized in the structure where half metallicity occurs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

C1b compounds with 18 valence electrons are semiconducting. It will be shown that doping with electrons results in half-metallic ferromagnets, similar to the case of diluted semiconductors. CoTiSb is known to be a semiconducting C1b compound. Doping by Fe is expected to result in ferromagnetic order. It was found that Ti can be replaced by up to about 10% Fe while its crystal structure still remains C1b, which was proved by x-ray powder diffraction. Superconducting quantum interference device magnetometry revealed a magnetic moment of 0.32μB/unit cell at 5 K. [ABSTRACT FROM AUTHOR]

Co2FeSi crystallizes in the ordered L21 structure as proven by x-ray diffraction and Möβbauer spectroscopy. The magnetic moment of Co2FeSi was measured to be about 6μB at 5 K. Magnetic circular dichroism spectra excited by soft x-rays were taken to determine the element-specific magnetic moments of Co and Fe. The Curie temperature was measured with different methods to be (1100±20)K. Co2FeSi was found to be the Heusler compound as well as the half-metallic ferromagnet with the highest magnetic moment and Curie temperature. [ABSTRACT FROM AUTHOR]

A concept is presented serving to guide in the search for materials with high spin polarization. It is shown that the magnetic moment of half-metallic ferromagnets can be calculated from the generalized Slater-Pauling rule. Furthermore, it was found empirically that the Curie temperature of Co2-based Heusler compounds can be estimated from a seemingly linear dependence on the magnetic moment. As a successful application of these simple rules, it was found that Co2FeSi is, actually, the half-metallic ferromagnet exhibiting the highest magnetic moment and the highest Curie temperature measured for a Heusler compound. [ABSTRACT FROM AUTHOR]