Ferromagnetic semiconductors (FMSs) featuring a high Curie transition temperature ( Tc) and a strong correlation between itinerant carriers and localized magnetic moments are of tremendous importance for the development of practical spintronic devices. The realization of such materials hinges on the ability to generate and manipulate a high density of itinerant spin-polarized carriers and the understanding of their responses to external stimuli. In this study, we demonstrate the ability to tune magnetic ordering in the p-type FMS FeSb2- xSn xSe4 (0 ≤ x ≤ 0.20) through carrier density engineering. We found that the substitution of Sb by Sn FeSb2- xSn xSe4 increases the ordering of metal atoms within the selenium crystal lattice, leading to a large separation between magnetic centers. This results in a decrease in the Tc from 450 K for samples with x ≤ 0.05 to 325 K for samples with 0.05 < x ≤ 0.2. In addition, charge disproportionation arising from the substitution of Sb3+ by Sn2+ triggers the partial oxidation of Sb3+ to Sb5+, which is accompanied by the generation of both electrons and holes. This leads to a drastic decrease in the electrical resistivity and thermopower simultaneously with a large increase in the magnetic susceptibility and saturation magnetization upon increasing Sn content. The observed bipolar doping induces a very interesting temperature-induced quantum electronic transition (Lifshitz transition), which is manifested by the presence of an anomalous peak in the resistivity curve simultaneously with a reversal of the sign of a majority of the charge carriers from hole-like to electron-like at the temperature of maximum resistivity. This study suggests that while there is a strong correlation between the overall magnetic moment and free carrier spin in FeSb2- xSn xSe4 FMSs, the magnitude of the Curie temperature strongly depends on the spatial separation between localized magnetic centers rather than the concentration of magnetic atoms or the density of itinerant carriers.
Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text E. Leith, C. Chen, H. Chen, Y. Chen, D. Dilworth, J. Lopez, J. Rudd, P.-C. Sun, J. Valdmanis, and G. Vossler, "Imaging through scattering media with holography," J. Opt. Soc. Am. A 9, 1148-1153 (1992) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article
Understanding the nature and origin of high-temperature ferromagnetic-like ordering in complex semiconducting transition metal selenides, such as FeBi2Se4, is extremely important and could shed light on novel approaches to develop high-Tc ferromagnetism in traditional semiconductors. Here, we report on the effect of partial substitution of Fe by Sn on the distribution of magnetic centers within the Fe1–xSnxBi2Se4 crystal lattice and its impact on the electronic and magnetic properties. Several compositions of the Fe1–xSnxBi2Se4 (0.1 ≤ x ≤ 0.5) solid solution were synthesized by combining high-purity elements in the respective stoichiometric ratios. Powder X-ray diffraction suggests that the synthesized phases are isostructural with the parent compound, FeBi2Se4, despite the large difference in the ionic radii of Fe2+ and Sn2+ in octahedral coordination. Single-crystal X-ray diffraction reveals increased ordering in the distribution of Fe2+, Sn2+, and Bi3+ atoms in various metal sites within the crystal structure, with full atomic ordering reached for the Fe0.5Sn0.5Bi2Se4 (x = 0.5) composition. High-temperature direct current (dc) magnetic susceptibility measurements reveal that all Fe1–xSnxBi2Se4 samples remain ferromagnetic over a wide temperature range and the Curie transition temperature, Tc, decreases from ∼450 K for compositions with x ≤ 0.15 to 325 K for compositions with high Sn content. The observed drop in Tc is ascribed to an increased separation between the magnetic centers for compositions with x > 0.15. Hall effect measurements confirm the n-type semiconducting nature of all compounds. Interestingly, the carrier density of Fe1–xSnxBi2Se4 samples gradually decreases with decreasing temperature down to 150 K, below which a remarkable transition from semiconducting to metallic behavior is observed for compositions with x ≥ 0.25.
Abstract Characterization of an Amazonian, laterite‐doped, kaolinitic soil (LK) or “lateritic soil” and laterite‐doped metakaolin (LMK) calcined at two distinct rates, as well as granite‐marble (GM) particulate industrial wastes was performed by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X‐ray diffraction (XRD), energy dispersive X‐ray fluorescence (XRF) spectrometry, and particle size and distribution analysis. In addition, an LMK geopolymer (GP) and a lateritic metakaolin‐based GP reinforced with granite‐marble composite (LMKGP‐GM) were tested for water resistance and for mechanical strength. XRD and XRF were used to investigate the composition of the composite materials, while XRD confirmed the formation of GP. Just as in the case of highly reactive commercial metakaolin used in construction, according to this study, lateritic soil‐based metakaolin presented similar characteristics. Therefore, it could be used in the development of more sustainable ceramics and construction materials, including the use of GM waste as a reinforcing phase/aggregate.
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