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Register a new userCanted Antiferromagnetism in the Quasi-1D Iron Chalcogenide BaFe$_{2}$Se$_{4}$
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We report the synthesis and physical properties studies of quais-1D iron chalcogenide $rm BaFe_2Se_4$ which shares the $rm FeSe_4$ tetrahedra building motif commonly seen in the iron chalcogenide superconductors. A high-quality polycrystalline sample was achieved by solid-state reaction method and characterized by X-ray diffraction, electrical resistivity, magnetic susceptibility and neutron diffraction measurements. $rm BaFe_2Se_4$ is a narrow gap semiconductor that magnetically orders at $sim$ 310 K. Both neutron powder diffraction results and isothermal M-H loops suggest a canted antiferromagnetic structure where Fe sublattice are antiferromagnetically ordered along the c-axis quasi-1D chain direction, resulting in a net ferromagnetic moment in the perpendicular direction along the a-axis with tilted angle of 18.7$^circ$ towards the b-axis.
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The magnetism in the saw-tooth lattice of Mn in the olivine chalcogenides, Mn$_2$SiS$_{4-x}$Se$_x$ ($x$ = 1$textendash$4) is studied in detail by analyzing their magnetization, specific heat and thermal conductivity properties and complemented with density functional theory calculations. The air-stable chalcogenides are antiferromagnets and show a linear trend in the transition temperature, $T_N$ as a function of Se-content ($x$) which shows a decrease from $T_N approx$ 86~K for {mss} to 66~K for {msse}. Additional new magnetic anomalies are revealed at low temperatures for all the compositions. Magnetization irreversibilities are also observed as a function of $x$. The specific heat and the magnetic entropy indicate the presence of short-range spin fluctuations in Mn$_2$SiS$_{4-x}$Se$_x$. A spin-flop antiferromagnetic phase transition in the presence of applied magnetic field is present in Mn$_2$SiS$_{4-x}$Se$_x$, where the critical field for the spin flop increases from $x$ = 0 towards 4 in a non-linear fashion. Density functional theory calculations show that an overall antiferromagnetic structure with ferromagnetic coupling of the spins in the $ab$-plane minimizes the total energy. The band structures calculated for mss and msse reveal features near the band edges similar to those reported for Fe-based olivines suggested as thermoelectrics; however the experimentally determined thermal transport data do not support superior thermoelectric features. The transition from long-range magnetic order in mss to short-range order and spin fluctuations in msse is explained using the variation of the Mn-Mn distances in the triangle units that constitutes the saw-tooth lattice upon progressive replacement of sulphur with selenium.
We report the low-temperature properties of phase-pure single crystals of the half-Heusler compound CuMnSb grown by means of optical float-zoning. The magnetization, specific heat, electrical resistivity, and Hall effect of our single crystals exhibit an antiferromagnetic transition at $T_{mathrm{N}} = 55~mathrm{K}$ and a second anomaly at a temperature $T^{*} approx 34~mathrm{K}$. Powder and single-crystal neutron diffraction establish an ordered magnetic moment of $(3.9pm0.1)~mu_{mathrm{B}}/mathrm{f.u.}$, consistent with the effective moment inferred from the Curie-Weiss dependence of the susceptibility. Below $T_{mathrm{N}}$, the Mn sublattice displays commensurate type-II antiferromagnetic order with propagation vectors and magnetic moments along $langle111rangle$ (magnetic space group $R[I]3c$). Surprisingly, below $T^{*}$, the moments tilt away from $langle111rangle$ by a finite angle $delta approx 11^{circ}$, forming a canted antiferromagnetic structure without uniform magnetization consistent with magnetic space group $C[B]c$. Our results establish that type-II antiferromagnetism is not the zero-temperature magnetic ground state of CuMnSb as may be expected of the face-centered cubic Mn sublattice.
We report on the new compound UCu${}_9$Sn${}_4$ which crystallizes in the tetragonal structure emph{I}4/emph{mcm} with lattice parameters $a = 8.600{rmAA}$ and $c = 12.359{rmAA}$. This compound is isotyp to the ferromagnetic systems RECu${}_9$Sn${}_4$ (RE = Ce, Pr, Nd) with Curie temperatures $T{}rm_C$ = 5.5 K, 10.5 K and 15 K, respectively. UCu${}_9$Sn${}_4$ exhibits an uncommon magnetic behavior resulting in three different electronic phase transitions. Below 105 K the sample undergoes a valence transition accompanied by an entropy change of 0.5 Rln2. At 32 K a small hump in the specific heat and a flattening out in the susceptibility curve probably indicate the onset of helical spin order. To lower temperatures a second transition to antiferromagnetic ordering occurs which develops a small ferromagnetic contribution on lowering the temperature further. These results are strongly hinting for canted antiferromagnetism in UCu${}_9$Sn${}_4$.
Quasi-one-dimensional iron-based ladders and chains, with the 3$d$ iron electronic density $n = 6$, are attracting considerable attention. Recently, a new iron chain system Ba$_2$FeS$_3$, also with $n = 6$, was prepared under high-pressure and high-temperature conditions. Here, the magnetic and electronic phase diagrams are theoretically studied for this quasi-one-dimensional compound. Based on first-principles calculations, a strongly anisotropic one-dimensional electronic band behavior near the Fermi level was observed. In addition, a three-orbital electronic Hubbard model for this chain was constructed. Introducing the Hubbard and Hund couplings and studying the model via the density matrix renormalization group (DMRG) method, we studied the ground-state phase diagram. A robust staggered $uparrow$-$downarrow$-$uparrow$-$downarrow$ AFM region was unveiled in the chain direction, consistent with our density functional theory (DFT) calculations. Furthermore, at intermediate Hubbard $U$ coupling strengths, this system was found to display an orbital selective Mott phase (OSMP) with one localized orbital and two itinerant metallic orbitals. At very large $U/W$ ($W$ = bandwidth), the system displays Mott insulator characteristics, with two orbitals half-filled and one doubly occupied. Our results for high pressure Ba$_2$FeS$_3$ provide guidance to experimentalists and theorists working on this one-dimensional iron chalcogenide chain material.
The quasi-one-dimensional spin ladder compounds, BaFe$_2$S$_3$ and BaFe$_2$Se$_3$, are investigated by infrared spectroscopy and density functional theory (DFT) calculations. We observe strong anisotropic electronic properties and an optical gap in the leg direction that is gradually filled above the antiferromagnetic (afm) ordering temperature, turning the systems into a metallic phase. Combining the optical data with the DFT calculations we associate the optical gap feature with the $p$-$d$ transition that appears only in the afm ordered state. Hence, the insulating ground state along the leg direction is attributed to Slater physics rather than Mott-type correlations.
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