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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]

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]

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]

Spintronic is a multidisciplinary field and a new research area. New materials must be found for satisfying the different types of demands. The search for stable half-metallic ferromagnets and ferromagnetic semiconductors with Curie temperatures higher than room temperature is still a challenge for solid state scientists. A general understanding of how structures are related to properties is a necessary prerequisite for material design. Computational simulations are an important tool for a rational design of new materials. The new developments in this new field are reported from the point of view of material scientists. The development of magnetic Heusler compounds specifically designed as material for spintronic applications has made tremendous progress in the very recent past. Heusler compounds can be made as half-metals, showing a high spin polarization of the conduction electrons of up to 100% in magnetic tunnel junctions. High Curie temperatures were found in Co2-based Heusler compounds with values up to 1120K in Co2FeSi. The latest results at the time of writing are a tunnelling magnet resistance (TMR) device made from the Co2FeAl0.5Si0.5 Heusler compound and working at room temperature with a (TMR) effect higher than 200%. Good interfaces and a well-ordered compound are the precondition to realize the predicted half-metallic properties. The series Co2FeAl1-x Six is found to exhibit half-metallic ferromagnetism over a broad range, and it is shown that electron doping stabilizes the gap in the minority states for x = 0.5. This might be a reason for the exceptional temperature behaviour of Co2FeAl0.5Si0.5 TMR devices. Using x-ray diffraction (XRD), it was shown conclusively that Co2FeAl crystallizes in the B2 structure whereas Co2FeSi crystallizes in the L21 structure. For the compounds Co2FeGa or Co2FeGe, with Curie temperatures expected higher than 1000 K, the standard XRD technique using laboratory sources cannot be used to easily distinguish between the two structures. For this reason, the EXAFS technique was used to elucidate the structure of these two compounds. Analysis of the data indicated that both compounds crystallize in the L21 structure which makes these two compounds suitable new candidates as materials in magnetic tunnel junctions. [ABSTRACT FROM AUTHOR]

This work reports on the magnetostructural properties of Co2-xFe1+xSi with 02FeSi is a half-metallic ferromagnet with high Curie temperature and was suggested as candidate for a high tunneling magnetoresistance. Changing the Fe content allows to tune its magnetic properties. It is demonstrated that the solid solution series Co2-xFe1+xSi is perfectly ordered. 57Fe Mössbauer spectroscopy was used to determine the local hyperfine magnetic fields of the Fe atoms. Two different hyperfine magnetic fields are detected in samples with x>0. Changes in the relative intensities indicate the well ordered substitution of Co by Fe atoms [ABSTRACT FROM AUTHOR]

Diluted magnetic semiconductors were prepared by substituting titanium in the semiconducting compound CoTiSb with iron. The structural, electronic, and magnetic properties of the pure and doped materials were investigated. It was found that substitution of up to 10% Ti by Fe does not affect the crystalline structure. Self-consistent calculations of the electronic structure predict the material to be a half-metallic ferromagnet. The Curie temperature of the Fe substituted alloy is far above room temperature (>700 K), thus making that material a serious candidate for future electronic applications, in particular, for magnetoelectronics and spintronics. [ABSTRACT FROM AUTHOR]

This work reports on structural and magnetic investigations of the Heusler compound Co2FeSi. X-ray diffraction and Mößbauer spectrometry indicate an ordered L21 structure. Magnetic measurements by means of x-ray magnetic circular dichroism and magnetometry revealed that this compound is, currently, the material with the highest magnetic moment (6μB) and Curie temperature (1100 K) in the classes of Heusler compounds as well as half-metallic ferromagnets. [ABSTRACT FROM AUTHOR]

Abstract: Ferromagnetic -based Heusler compounds have generated increasing interest over the last few years because of their peculiar electronic structure. They exhibit a band gap for the electrons of one direction and are metallic for the other. Further, they cover a very wide range of magnetic moments and Curie temperatures. Despite lot of efforts in theory and experiment to describe bulk materials and thin films, there are some marked discrepancies between observed and predicted properties of these materials. These discrepancies appear not only across but also within synthesis methods as well as in the theoretical predictions. In this contribution, the electronic structure of YSi(Y=Sc, Ti; V, Cr, Mn, Fe) is discussed. In particular, the magnetic moments and the minority band gaps in these materials have been examined respecting electron–electron correlation in the calculations. [Copyright &y& Elsevier]

Abstract: In this article the Co2 based Heusler compounds are discussed as potential materials for spin voltage generation. The compounds were synthesized by arc melting and consequent annealing. Band structure calculations were performed which 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. [Copyright &y& Elsevier]

The local atomic environments and magnetic properties were investigated for a series of Co1+xFe2-xSi (0≤x≤1) Heusler compounds. While the total magnetic moment in these compounds increases with the number of valance electrons, the highest Curie temperature (TC) in this series was found for Co1.5Fe1.5Si, with a TC of 1069 K (24 K higher than the well-known Co2FeSi). 57Fe Mössbauer spectroscopy was used to characterize the local atomic order and to estimate the Co and Fe magnetic moments. Consideration of the local magnetic moments and the exchange integrals is necessary to understand the trend in TC. [ABSTRACT FROM AUTHOR]