The cubic Heusler compound Mn1.5FeV0.5Al with the L21 Heusler structure is the first fully compensated half-metallic ferrimagnet with 24 valence electrons. The ferrimagnetic state can be tuned by ...changing the composition such that the compensation point appears at finite temperatures ranging from 0 K up to 226 K, while retaining half-metallicity in the system. In this paper, the structural, magnetic and transport properties of the Mn-Fe-V-Al system are discussed. Magnetic reversal and a change of sign of the anomalous Hall effect were observed at the compensation point, which gives rise to a sublattice spin-crossing. These materials present new possibilities for potential spintronic devices because of their advantageous properties such as imperceptibility to external fields, lower power consumption and ultrafast switching in the THz region.
Alloys based on the half-Heusler compound TiNiSn with the addition of Mn or with a substitution of Ti by Mn are investigated as high-temperature thermoelectric materials. In both materials an ...intrinsic phase separation is observed, similar to TiNiSn where Ti has been partially substituted by Hf, with increasing Mn concentration the phase separation drastically reduces the lattice thermal conductivity while the power factor is increased. The thermoelectric performance of the n-type conducting alloy can be optimized both by substitution of Ti by Mn as well as the addition of Mn.
The carrier concentration in the p-type half-Heusler compound Ti0.3Zr0.35Hf0.35CoSb1−xSnx was optimized, which is a fundamental approach to enhance the performance of thermoelectric materials. The ...optimum carrier concentration is reached with a substitution level x = 0.15 of Sn, which yields the maximum power factor, 2.69 × 10−3 W m−1 K−2, and the maximum ZT = 0.8. This is an enhancement of about 40% in the power factor and the figure of merit compared to samples with x = 0.2. To achieve low thermal conductivities in half-Heusler compounds, intrinsic phase separation is an important key point. The present work addresses the influence of different preparation procedures on the quality and reproducibility of the samples, leading to the development of a reliable fabrication method.
Hydrothermal treatment (HTT) offers the potential to upgrade low-value biomass such as digestate (DG) or forest residue (FR) by producing solids and liquids for material use or energetic utilization. ...In this study, microwave-assisted HTT experiments with DG and FR as feedstocks were executed at different temperatures (130, 150, 170 °C) and with different holding times (30, 60, 90 min) to determine the influences on product properties (ash and elemental concentrations, calorific values and chemical compounds). In general, DG and FR reacted differently to HTT. For the DG solids, for instance, the ash concentration was reduced to 8.68%DM at 130 °C (initially 27.67%DM), and the higher heating value increased from 16.55 MJ/kgDM to 20.82 MJ/kgDM at 170 °C, while the FR solids were affected only marginally. Elements with importance for emissions in combustion were leached out in both HTT solids. The DG and FR liquids contained different chemical compounds, and the temperature or holding time affected their formation. Depending on the designated application of HTT, less severe conditions can deliver better results. It was demonstrated that different low-temperature HTT conditions already induce strong changes in the product qualities of DG and FR. Optimized interactions between process parameters (temperature, holding time and feedstock) might lead to better cost–benefit effects in HTT.
We report the transport properties of the proposed Heusler topological insulators YPtSb, LaPtBi, and LuPdSb. All compounds show ultrahigh hole mobility with value of 4124, 4275, and 1800 cm super(2) ...V super(-1) s super(-1) for YPtBi, LaPtBi, and LuPdSb, respectively, at 300 K. The temperature dependence of mobility shows strong and weak phonon scattering for LaPtBi and LuPdSb, respectively, while YPtSb shows strong impurity scattering. These ultrahigh values of the mobility are not only due to gaplessness but also to the presence of linear dispersion of the bands close to the Fermi energy, where charge carriers behave like relativistic particles. Furthermore, nonsaturating magnetoresistance (MR) is observed in the temperature range 2-300 K that shows linear behavior at high fields. A tentative relationship between the linear MR and mobility is discussed, which indicates that the mobility controls the linear part of MR.
In comparison to lignocellulosic biomass, which is suitable for thermo-chemical valorization, the organic fraction of municipal solid waste (OFMSW) is mainly treated via composting or anaerobic ...digestion (AD). An efficient utilization of OFMSW is difficult due to variations in its composition. Based on the characteristics of OFMSW, hydrothermal treatment (HTT) experiments at temperatures < 200 °C as an alternative OFMSW-processing were evaluated in this study. The raw OFMSW was characterized with a dry matter (DM)-based organic dry matter (oDM) content of 77.88 ± 1.37 %DM and a higher heating value (HHV) of 15,417 ± 1258 J/gDM. Through HTT at 150, 170 and 185 °C, the oDM contents as well as H/C and O/C ratios were lowered while the HHV increased up to 16,716 ± 257 J/gDM. HTT led to improved fuel properties concerning ash melting, corrosion stress and emission behavior. Negative consequences of the HTT process were higher contents of ash in the biochar as well as accumulated heavy metals. In the sense of a bioeconomy, it could be beneficial to first convert raw OFMSW into CH4 through AD followed by HTT of the AD-digestate for the generation of solid fuels and liquid products. This could increase the overall utilization efficiency of OFMSW.
•Bulk sensitivity of HAXPES was used to explore the electronic structure of several Heusler compounds in form of bulk materials and thin films.•Strong changes of the electronic structure Heusler ...shape memory Mn2NiGa appear at the phase transition.•HAXPES of C1b Heusler compounds with narrow band gap showed the existence of in gap states close to the Fermi energy.•Linear dichroism in hard X-ray photoelectron spectroscopy (LDAD-HAXPES) was used to study the angular asymmetry in photoemission from the valence states of three kinds of Heusler compounds.
Photoelectron spectroscopy (PES) has evolved into the most relevant, powerful, and nondestructive method for investigating atoms, molecules, and solids. In particular, hard X-ray photoelectron spectroscopy (HAXPES) has emerged as a powerful tool for investigating the bulk electronic structure of materials in a variety of applied fields such as chemistry, physics, and materials science. In addition, PES was used for investigating the symmetries of various materials’ electronic structures. However, thus far, such studies have been restricted to atoms, molecules, adsorbates, and surfaces because low-energy (<1keV) electrons have limited probing depths. This is disadvantageous because three-dimensional (3D) bulk states cannot be studied. The present work demonstrates that this drawback can be eliminated by using hard X-rays with variable polarization for excitation. In the current study, this issue was investigated using several Heusler compounds, which have been attracting increasing levels of interest. There are more than 2000 Heusler compounds in total. Owing to their tunable electronic structures, Heusler compounds exhibit multifarious properties useful for spintronic, optoelectronic, shape memory, and thermoelectric applications. Herein, we report the results of bulk-sensitive, high energy photoelectron spectroscopy of the valence bands of several Heusler compounds for various applications. It is shown that the measured valence band spectra are clearly resolved and are in good agreement with the first-principles calculations of the compounds’ electronic structures.
New Mn2-based Heusler Compounds Kreiner, Guido; Kalache, Adel; Hausdorf, Steffen ...
Zeitschrift für anorganische und allgemeine Chemie (1950),
April 2014, Volume:
640, Issue:
5
Journal Article
Peer reviewed
Mn2‐based Heusler compounds have attracted a great deal of interest as half‐metallic ferri‐ and ferromagnets and as materials for spintronic applications. In this paper, we report the synthesis, ...crystal structure, and disorder type of the new Heusler compounds Mn2RuGe, Mn2RhGa, and the redetermination of the crystal structure of Mn2RuSn. They crystallize cubic with L21b structure type in Fm$\bar{3}$m, which is an inverse Heusler structure with a transition metal disorder of the type (Mn0.5,Y0.5)2MnZ (Y = Ru or Rh and Z = Ge, Ga or Sn). It is shown that an inverse Heusler structure can generally gain stability through the configurational part of the entropy of mixing at elevated temperatures without loosing too much enthalpy in the configurational part of the enthalpy of mixing owing to a special bond arrangement in the inverse type structure. The enthalpy of formation of transition‐metal‐based Heusler compounds and Al, Ga, and Ge as the main group metals obtained from DFT calculations and experimental data are used to confirm Burch's rule, which predicts the stability of transition‐metal‐based inverse Heusler compounds. Alloying tendencies as manifested in binary phase diagrams and the enthalpies obtained from the Miedema model are correlated with the stability of Heusler compounds. Burch's rule is in excellent agreement with the current available experimental data. The DFT data and general alloying tendencies show that deviations are expected from this rule. Miedema's model allows the estimation of the enthalpy of formation for the transition‐ and main group metal‐based Heusler compounds, except for those having period 6 elements and Pd.
Phase transitions and magnetic properties of shape-memory materials can be tailored by tuning the size of the constituent materials, such as nanoparticles. However, owing to the lack of suitable ...synthetic methods for size-controlled Heusler nanoparticles, there is no report on the size dependence of their properties and functionalities. In this contribution, we present the first chemical synthesis of size-selected Co-Ni-Ga Heusler nanoparticles. We also report the structure and magnetic properties of the biphasic Co-Ni-Ga nanoparticles with sizes in the range of 30-84 nm, prepared by a SBA-15 nanoporous silica- templated approach. The particle sizes could be readily tuned by controlling the loading and concentration of the precursors. The fractions and crystallite sizes of each phase of the Co-Ni-Ga nanoparticles are closely related to their particle size. Enhanced magnetization and decreased coercivity are observed with increasing particle size. The Curie temperature （To） of the Co-Ni-Ga nanoparticles also depends on their size. The 84 nm-sized particles exhibit the highest Tc （≈ 1,174 K） among all known Heusler compounds. The very high Curie temperatures of the Co-Ni-Ga nanoparticles render them promising candidates for application in high-temperature shape memory alloy-based devices.
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