Antiferromagnetic semiconductors are new alternative materials for spintronic applications and spin valves. In this work, we report a detailed investigation of two antiferromagnetic semiconductors AMnAs (A = Li, LaO), which are isostructural to the well-known LiFeAs and LaOFeAs superconductors. Here we present a comparison between the structural, magnetic, and electronic properties of LiMnAs, LaOMnAs, and related materials. Interestingly, both LiMnAs and LaOMnAs show a variation in resistivity with more than five orders of magnitude, making them particularly suitable for use in future electronic devices. Neutron and x-ray diffraction measurements on LiMnAs show a magnetic phase transition corresponding to the Néel temperature of 373.8 K, and a structural transition from the tetragonal to the cubic phase at 768 K. These experimental results are supported by density functional theory calculations.
This work reports on the electronic and crystalline structure and the mechanical, magnetic, and transport properties of the polycrystalline Heusler compound Co 2 MnGe. The crystalline structure was examined in detail by extended x-ray absorption fine-structure spectroscopy and anomalous x-ray diffraction. The compound exhibits a well-ordered L2 1 structure as is typical for Heusler compounds with 2:1:1 stoichiometry. The low-temperature magnetic moment agrees well with the Slater-Pauling rule and indicates a half-metallic ferromagnetic state of the compound, as is predicted by ab initio calculations. Transport measurements and hard x-ray photoelectron spectroscopy were performed to explain the electronic structure of the compound. The obtained valence band spectra exhibit small energy shifts that are the result of the photoexcitation process, whereas electron-electron correlation in the ground state is negligible. The vibration and mechanical properties of the compound were calculated. The observed hardness values are consistent to a covalent-like bonding of Co 2 MnGe.
The compounds LiAlSi and LiAlGe were synthesized and their thermoelectric properties and temperature stability were investigated. The samples were synthesized by arc melting of the constituent elements. For the determination of the structure type and the lattice parameter, x-ray powder diffraction was used. Both compounds were of the C1 (b) structure type. The stability of the compounds was investigated by differential thermal analysis and thermal gravimetry. The Seebeck coefficient and the electrical resistivity were determined in the temperature range from 2 K to 650 K. All compounds showed p-type behavior. The thermal conductivity was measured from 2 K to 400 K. The evaluation of the thermal conductivity yielded values as low as 2.4 W m(-1) K(-1) at 400 K for LiAlGe. The low values are ascribed to high mass fluctuation scattering and a possible rattling effect of the Li atoms
This work reports on the experimental investigation of wide band gap compounds LiMgZ (Z = P, As, Sb), which are promising candidates for opto-electronics and anode materials for lithium batteries. The compounds crystallize in the cubic (C1
b
) MgAgAs structure (space group
). The polycrystalline samples are synthesized by solid-state reaction methods. X-ray and neutron diffraction measurements show homogeneous, single-phased samples. The electronic properties are studied using the direct current method. Additionally, UV–Vis diffuse reflectance spectra are recorded in order to investigate the band gap nature. The measurements show that all compounds exhibit semiconducting behaviour with direct band gaps of 1.0–2.3 eV depending on the Z element. A decrease in the peak widths in the static 7Li nuclear magnetic resonance spectra with increasing temperature is observed, which can be directly related to an increase in Li ion mobility.
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