Search for: All records

We report a detailed study of the synthesis, composition, magnetic structure, and transport properties of a quasi-one-dimensional antiferromagnet FeBi4S7 that contains chains of edge-sharing FeS6 octahedra. High-resolution powder X-ray diffraction (PXRD) analysis, aided by variation of synthetic conditions, suggests that the true formula of the material is Fe1.2Bi3.8S7, due to the minor substitution of Fe into Bi sites. This finding is in agreement with crystal structure refinement from neutron powder diffraction data as well as with the small band gap of 0.23 eV determined from electrical transport measurements. Analysis of the neutron diffraction pattern collected below the antiferromagnetic ordering temperature of 64 K revealed ferromagnetic coupling between the Fe moments in the chains of FeS6 octahedra. The overall ordering, however, is antiferromagnetic due to the antiparallel arrangement of moments on neighboring chains. The collinear spin arrangement is described by a k-vector (1, 0, 1/2), which indicates doubling of the unit cell in the c direction and the loss of the C-centering translation as compared to the nuclear cell. The ferromagnetic nature of the sulfidebridged chains of Fe2+ ions in FeBi4S7, in contrast to the antiferromagnetic coupling between Fe moments in compounds with similar structural fragments, can be justified by the analysis of metric parameters that characterize the Fe−S bonding in these materials. 

We report a transport study on Pd₃In₇which displays multiple Dirac type-II nodes in its electronic dispersion. Pd₃In₇is characterized by low residual resistivities and high mobilities, which are consistent with Dirac-like quasiparticles. For an applied magnetic field (μ₀H) having a non-zero component along the electrical current, we find a large, positive, and linear inμ₀Hlongitudinal magnetoresistivity (LMR). The sign of the LMR and its linear dependence deviate from the behavior reported for the chiral-anomaly-driven LMR in Weyl semimetals. Interestingly, such anomalous LMR is consistent with predictions for the role of the anomaly in type-II Weyl semimetals. In contrast, the transverse or conventional magnetoresistivity (CMR for electric fieldsE⊥μ₀H) is large and positive, increasing by 10³−10⁴% as a function ofμ₀Hwhile following an anomalous, angle-dependent power law$${\rho }_{{{{\rm{xx}}}}}\propto {({\mu }_{0}H)}^{n}$$${\rho }_{\mathrm{xx}}\propto {\left({\mu }_{0}H\right)}^n$withn(θ) ≤ 1. The order of magnitude of the CMR, and its anomalous power-law, is explained in terms of uncompensated electron and hole-like Fermi surfaces characterized by anisotropic carrier scattering likely due to the lack of Lorentz invariance.

 

We report a theoretical investigation of effects of Mn and Co substitution in the transition metal sites of the kagomé-lattice ferromagnet, Fe₃Sn₂. Herein, hole- and electron-doping effects of Fe₃Sn₂have been studied by density-functional theory calculations on the parent phase and on the substituted structural models of Fe_3−xM_xSn₂(M = Mn, Co;x= 0.5, 1.0). All optimized structures favor the ferromagnetic ground state. Analysis of the electronic density of states (DOS) and band structure plots reveals that the hole (electron) doping leads to a progressive decrease (increase) in the magnetic moment per Fe atom and per unit cell overall. The high DOS is retained nearby the Fermi level in the case of both Mn and Co substitutions. The electron doping with Co results in the loss of nodal band degeneracies, while in the case of hole doping with Mn emergent nodal band degeneracies and flatbands initially are suppressed in Fe_2.5Mn_0.5Sn₂but re-emerge in Fe₂MnSn₂. These results provide key insights into potential modifications of intriguing coupling between electronic and spin degrees of freedom observed in Fe₃Sn₂.

 

We report liquid-phase exfoliation (LPE) of bulk layered-structure semiconductor, MnIn 2 Se 4 , to nanoscale thick sheets by ultrasonication followed by sequential centrifugation at 2000, 5000, and 7500 rpm. The nanosheets exfoliated by LPE in isopropyl alcohol show an average thickness of 50, 40, and 14 nm, respectively. The smallest of these values corresponds approximately to ten 7-atom thick [Se–In–Se–Mn–Se–In–Se] layers that compose the bulk structure of MnIn 2 Se 4 . Both the bulk material and the exfoliated samples show photoluminescence, but the weak shoulder observed from the indirect band gap emission is obviously suppressed in the nanosheet samples as compared to the bulk sample. Similar to the bulk, the nanosheets isolated at 2000 and 5000 rpm exhibit spin-glass behavior with a freezing temperature of ∼3 K. In contrast, the nanosheets isolated at 7500 rpm do not exhibit any anomalies in their low-temperature magnetic behavior. These results demonstrate the possibility to extend the LPE technique to van-der-Waals materials with several-atom-thick layers.