Complex Transition Metal Chalcogenide Ferromagnetic Semiconductor with General Formula MSb2Se4 (M=Mn , Fe): Synthesis and Characterization.

We report two new magnetic semiconducting compounds (FeSb2Se4 and MnSb2Se4), which are subsequently used as template for the investigation of the effect of electronic structure engineering of low band gap magnetic semiconductor in the magnetic behavior and the Curie ferromagnetic to paramagnetic transition temperature (Tc). Compounds were synthesized by solid-state reaction of the elements at moderate temperature. Both compounds crystallize in the monoclinic crystal system with space group C2/m (#12). Their crystal structure can be viewed as consisting of two types of building units, denoted A and B alternate along [001]. The unit A is built of paired rods of face-sharing monocapped trigonal prisms around Sb atoms alternating along the a-axis with a single chain of edge-sharing octahedra around the magnetic M (Fe, Mn) atoms. The unit B is a NaCl-type block separating adjacent units A, within which chains of edge-sharing octahedral around Sb atoms alternate along the a-axis with a single chain of edge-sharing octahedra around the magnetic M (Fe, Mn). Temperature dependent measurements of the magnetic susceptibility and electrical conductivity revealed that FeSb2Se4 is a high temperature p-type ferromagnetic semiconductor with an electrical conductivity of ~ 2 S/cm and the Curie transition temperature Tc ~ 450K, whereas a dominant antiferromagnetic ordering was observed in the MnSb2Se4 compound. To probe the effect of changes in the electronic transport properties in FeSb2Se4 and MnSb2Se4 on their magnetic behavior, the solid-solution series, Fe1-xSb2SnxSe4, FeSb2-xSnxSe4, MnSb2-xSnxSe4, and FeSb2Se4-xTex were investigated. All Fe containing compositions (except the FeSb2Se4-xTex series (x= 1, 2, 3 and 4) were found to be isostructural with FeSb2Se4 and showed a ferromagnetic ordering up to 600K with magnetic and electronic transitions at 130K,321K, 400K and 440K. These transitions were found also to be related to structural changes upon heating or cooling from 300K. The transitions at 130K, 400K and 440K disappear with increasing concentration of Sn indicating the structural effect is annealed with increasing Sn content. The materials exhibit large positive values of the thermopower and optical measurements revealed an optical band gap of 0.32eV, suggesting that the substituted FeSb2Se4 families of compounds are p-type narrows band gap semiconductors.PhDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/102463/1/djieuteh_1.pd

Crystal Structure of FePb 4 Sb 6 Se 14 and its Structural Relationship with FePb 3 Sb 4 Se 10

Single crystals of FePb 4 Sb 6 Se 14 , were obtained from solid‐state combination of high purity elemental powders at 873K for three days. Single crystal X‐ray structure determination revealed that the compound crystallizes in the monoclinic space group P 2 1 / c (no. 14) and adopts the structure of Jamesonite (FePb 4 Sb 6 S 14 ). The structure contains two crystallographically independent lead atoms with monocapped and bicapped trigonal prismatic coordinations, three antimony atoms located in a distorted octahedral environment and one iron atom occupying a flattened octahedral coordination. Neighboring monocapped and bicapped trigonal prims around lead atoms share faces and edges to build a corrugated layer parallel to the ac plane. Octahedrally coordinated antimony atoms share edges to form one‐dimensional (1D) {SbSe} ∞ ribbons connecting adjacent corrugated layers. The distortion of the octahedral coordination around antimony atoms within the {SbSe} ∞ ribbons with the longest bond pointing towards the center of the ribbon, suggests the stereochemical activity of antimony lone‐pairs with their electron clouds pointing towards the center of the {SbSe} ∞ ribbon. The three dimensional framework resulting from the connectivity between the corrugated layers and the {SbSe} ∞ ribbons, contains isolated cylindrical voids parallel to [100] which are filled by a 1D Fe n Se 4n+2 straight chain of edge‐sharing FeSe 6 octahedra. The crystal structure of FePb 4 Sb 6 Se 14 is closely related to that of FePb 3 Sb 4 Se 10 as they are formed by similar building units with different sizes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95198/1/2549_ftp.pd

1H and 13C NMR assignments for a series of Diels–Alder adducts of anthracene and 9‐substituted anthracenes

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111949/1/mrc4268.pd

Chemical Manipulation of Magnetic Ordering in Mn_1–<i>x</i>Sn_<i>x</i>Bi₂Se₄ Solid–Solutions

Several compositions of manganese–tin–bismuth selenide solid–solution series, Mn_1–<i>x</i>Sn_<i>x</i>Bi₂Se₄ (<i>x</i> = 0, 0.3, 0.75), were synthesized by combining high purity elements in the desired ratio at moderate temperatures. X-ray single crystal studies of a Mn-rich composition (<i>x</i> = 0) and a Mn-poor phase (<i>x</i> = 0.75) at 100 and 300 K revealed that the compounds crystallize isostructurally in the monoclinic space group <i>C</i>2/<i>m</i> (no.12) and adopt the MnSb₂Se₄ structure type. Direct current (DC) magnetic susceptibility measurements in the temperature range from 2 to 300 K indicated that the dominant magnetic ordering within the Mn_1–<i>x</i>Sn_<i>x</i>Bi₂Se₄ solid–solutions below 50 K switches from antiferromagnetic (AFM) for MnBi₂Se₄ (<i>x</i> = 0), to ferromagnetic (FM) for Mn_0.7Sn_0.3Bi₂Se₄ (<i>x</i> = 0.3), and finally to paramagnetic (PM) for Mn_0.25Sn_0.75Bi₂Se₄ (<i>x</i> = 0.75). We show that this striking variation in the nature of magnetic ordering within the Mn_1–<i>x</i>Sn_<i>x</i>Bi₂Se₄ solid–solution series can be rationalized by taking into account: (1) changes in the distribution of magnetic centers within the structure arising from the Mn to Sn substitutions, (2) the contributions of spin-polarized free charge carriers resulting from the intermixing of Mn and Sn within the same crystallographic site, and (3) a possible long-range ordering of Mn and Sn atoms within individual {M}_<i>n</i>Se_4<i>n</i>+2 single chain leading to quasi isolated {MnSe₆} octahedra spaced by nonmagnetic {SnSe₆} octahedra

Donor and acceptor impurity-driven switching of magnetic ordering in MnSb2-xSnxSe4

The ability to manipulate the electronic structure of the low-dimensional magnetic semiconductor MnSb2Se4via isomorphic Sn/Sb substitutions enables independent investigation of the interactions of free carriers with localized magnetic moments and their effects on the predominant magnetic ordering in the p-type MnSb2-xSnxSe4 (0 ≤ x ≤ 0.25) semiconductors. We find a large increase in the electrical resistivity and thermopower with increasing Sn content suggesting a surprising decrease in the overall hole density. X-ray photoelectron spectroscopy reveals that Sn atoms enter the structure in the 2+ oxidation state, whereas a fraction of the remaining Sb3+ partially oxidizes to Sb5+ to maintain the electroneutrality of the compound. Therefore, we attribute the drop in the hole density to electron-hole compensation processes. Interestingly, magnetic susceptibility data reveal a remarkable switching of the dominant magnetic interaction from antiferromagnetism (AFM) (x = 0) to ferromagnetism (FM) with Tc ∼ 56 K for 0.05 ≤ x ≤ 0.15 samples and a reversal to AFM ordering for x \u3e 0.15. The Sn-dependent FM interaction in MnSb2-xSnxSe4 is rationalized within the context of the formation of overlapping bound magnetic polarons (BMPs) through the interactions between the added electrons/holes and localized moments of Mn2+ magnetic ions. This journal is © the Partner Organisations 2014

High‑<i>T</i>_c Ferromagnetism and Electron Transport in p‑Type Fe_1–<i>x</i>Sn_<i>x</i>Sb₂Se₄ Semiconductors

Single-phase polycrystalline powders of Fe_1–<i>x</i>Sn_<i>x</i>Sb₂Se₄ (<i>x</i> = 0 and 0.13) were synthesized by a solid-state reaction of the elements at 773 K. X-ray diffraction on Fe_0.87Sn_0.13Sb₂Se₄ single-crystal and powder samples indicates that the compound is isostructural to FeSb₂Se₄ in the temperature range from 80 to 500 K, crystallizing in the monoclinic space group <i>C</i>2/<i>m</i> (No. 12). Electron-transport data reveal a marginal alteration in the resistivity, whereas the thermopower drops by ∼60%. This suggests a decrease in the activation energy upon isoelectronic substitution of 13% Fe by Sn. Magnetic susceptibility and magnetization measurements from 2 to 500 K reveal that the Fe_1–<i>x</i>Sb₂Sn_<i>x</i>Se₄ phases exhibit ferromagnetic behavior up to ∼450 K (<i>x</i> = 0) and 325 K (<i>x</i> = 0.13). Magnetotransport data for FeSb₂Se₄ reveal large negative magnetoresistance, suggesting spin polarization of free carriers in the sample. The high-<i>T</i>_c ferromagnetism in Fe_1–<i>x</i>Sn_<i>x</i>Sb₂Se₄ phases and the decrease in <i>T</i>_c of the Fe_0.87Sn_0.13Sb₂Se₄ sample are rationalized by taking into account (1) the separation between neighboring magnetic centers in the crystal structures and (2) the formation of bound magnetic polarons, which overlap to induce long-range ferromagnetic ordering

Coexistence of high-Tc ferromagnetism and n-type electrical conductivity in FeBi2Se4

The discovery of n-type ferromagnetic semiconductors (n-FMSs) exhibiting high electrical conductivity and Curie temperature (Tc) above 300 K would dramatically improve semiconductor spintronics and pave the way for the fabrication of spin-based semiconducting devices. However, the realization of high-Tc n-FMSs and p-FMSs in conventional high-symmetry semiconductors has proven extremely difficult due to the strongly coupled and interacting magnetic and semiconducting sublattices. Here we show that decoupling the two functional sublattices in the low-symmetry semiconductor FeBi2Se4 enables unprecedented coexistence of high n-type electrical conduction and ferromagnetism with Tc ≈ 450 K. The structure of FeBi2Se4 consists of well-ordered magnetic sublattices built of [FenSe4n+2]∞ single-chain edge-sharing octahedra, coherently embedded within the three-dimensional Bi-rich semiconducting framework. Magnetotransport data reveal a negative magnetoresistance, indicating spin-polarization of itinerant conducting electrons. These findings demonstrate that decoupling magnetic and semiconducting sublattices allows access to high-Tc n- and p-FMSs as well as helps unveil the mechanism of carrier-mediated ferromagnetism in spintronic materials

Geometrical Spin Frustration and Ferromagnetic Ordering in (Mn_<i>x</i>Pb_2–<i>x</i>)Pb₂Sb₄Se₁₀

Engineering the atomic structure of an inorganic semiconductor to create isolated one-dimensional (1D) magnetic subunits that are embedded within the semiconducting crystal lattice can enable chemical and electronic manipulation of magnetic ordering within the magnetic domains, paving the way for (1) the investigation of new physical phenomena such as the interactions between electron transport and localized magnetic moments at the atomic scale and (2) the design and fabrication of geometrically frustrated magnetic materials featuring cooperative long-range ordering with large magnetic moments. We report the design, synthesis, crystal structure and magnetic behavior of (Mn_<i>x</i>Pb_2–<i>x</i>)­Pb₂Sb₄Se₁₀, a family of three-dimensional manganese-bearing main-group metal selenides featuring quasi-isolated [(Mn_<i>x</i>Pb_2–<i>x</i>)₃Se₃₀]_∞ hexanuclear magnetic ladders coherently embedded and uniformly distributed within a purely inorganic semiconducting framework, [Pb₂Sb₄Se₁₀]. Careful structural analysis of the magnetic subunit, [(Mn_<i>x</i>Pb_2–<i>x</i>)₃Se₃₀]_∞ and the temperature dependent magnetic susceptibility of (Mn_<i>x</i>Pb_2–<i>x</i>)­Pb₂Sb₄Se₁₀, indicate that the compounds are geometrically frustrated 1D ferromagnets. Interestingly, the degree of geometrical spin frustration (f) within the magnetic ladders and the strength of the intrachain antiferromagnetic (AFM) interactions strongly depend on the concentration (<i>x</i> value) and the distribution of the Mn atom within the magnetic substructure. The combination of strong intrachain AFM interactions and geometrical spin frustration in the [(Mn_<i>x</i>Pb_2–<i>x</i>)₃Se₃₀]_∞ ladders results in a cooperative ferromagnetic order with exceptionally high magnetic moment at around 125 K. Magnetotransport study of the Mn₂Pb₂Sb₄Se₁₀ composition over the temperature range from 100 to 200 K revealed negative magnetoresistance (NMR) values and also suggested a strong contribution of magnetic polarons to the observed large effective magnetic moments

Pb₇Bi₄Se₁₃: A Lillianite Homologue with Promising Thermoelectric Properties

Pb₇Bi₄Se₁₃ crystallizes in the monoclinic space group <i>C</i>2/<i>m</i> (No. 12) with <i>a</i> = 13.991(3) Å, <i>b</i> = 4.262(2) Å, <i>c</i> = 23.432(5) Å, and β = 98.3(3)° at 300 K. In its three-dimensional structure, two NaCl-type layers A and B with respective thicknesses <i>N</i>₁ = 5 and <i>N</i>₂ = 4 [<i>N</i> = number of edge-sharing (Pb/Bi)­Se₆ octahedra along the central diagonal] are arranged along the <i>c</i> axis in such a way that the bridging monocapped trigonal prisms, PbSe₇, are located on a pseudomirror plane parallel to (001). This complex atomic-scale structure results in a remarkably low thermal conductivity (∼0.33 W m^–1 K^–1 at 300 K). Electronic structure calculations and diffuse-reflectance measurements indicate that Pb₇Bi₄Se₁₃ is a narrow-gap semiconductor with an indirect band gap of 0.23 eV. Multiple peaks and valleys were observed near the band edges, suggesting that Pb₇Bi₄Se₁₃ is a promising compound for both n- and p-type doping. Electronic-transport data on the as-grown material reveal an n-type degenerate semiconducting behavior with a large thermopower (∼−160 μV K^–1 at 300 K) and a relatively low electrical resistivity. The inherently low thermal conductivity of Pb₇Bi₄Se₁₃ and its tunable electronic properties point to a high thermoelectric figure of merit for properly optimized samples