The magnetism of the A-site-ordered perovskite $\mathrm{LaM}{\mathrm{n}}_{3}{\mathrm{V}}_{4}{\mathrm{O}}_{12}$ is studied comprehensively by means of neutron powder diffraction experiments and theoretical calculations. Magnetic neutron diffraction results show that a rhombohedral 60\ifmmode^\circ\else\textdegree\fi{} spin structure emerges on the cubic lattice below a 44-K N\'eel transition. Ab initio electronic structure calculations confirm that high-spin ${\mathrm{Mn}}^{2+}$ moments are localized while V $3d$-band states are itinerant, and that the noncollinear 60\ifmmode^\circ\else\textdegree\fi{} spin structure is more stable than collinear ferromagnetic or G-type antiferromagnetic alternatives. Effective Heisenberg model calculations reveal that the appearance of such a nontrivial spin structure can be attributed to significant next-nearest-neighbor and third-nearest-neighbor magnetic interactions.
Frequency f and strain rate ̇εn dependences of linear dynamic shear modulus were measured for glassy epoxy network during uniaxial stretching processes. With increasing strain εn, the storage shear modulus G´ slightly decreased to a steady value appearing at post-yield strain-hardening range of strain. The loss shear modulus G˝ markedly increased in the same strain range, where G´ decreased, and then leveled off. These variations of G´ and G˝ indicated that the glassy structure in the epoxy network changed into more unstable ones by stretching. When compared at a fixed condition of α= ̇εn/f, the functional relation between strain-induced increment of G˝ and εn was identical independently of ̇εn of stretching. Thus, frequency dispersion of the nonlinear relaxation was found to be determined only by the relative distance from the timescale of deformation and the amount of imposed strain. Whereas the decrement of G´ at a fixed α was not superposable when plotted against εn, because of (εn ) ̇ dependence of their steady values. The variation of G´ was affected not only by destabilization of glassy structure due to deformation. The observed f and ̇εn dependences of G´-εn and G˝-εn relations for glassy epoxy network during stretching were qualitatively the same as those observed for poly(methyl methacrylate) (PMMA). Thus, the dependence on εn, f and ̇εn of the nonlinear relaxation under constant-speed deformation conditions reported here is presumably universal for glassy polymers. The strain-induced variation of G´ and G˝ was smaller for epoxy network compared with PMMA stretched exactly at the identical condition. This result indicates that glassy structures in the epoxy network before stretching are more unstable because of constraint arising from crosslinked molecular structures.
Boron-based two-dimensional (2D) materials are an excellent platform for nanoelectronics applications. Rhombohedral boron monosulfide (r-BS) is attracting particular attention because of its unique layered crystal structure suitable for exploring various functional properties originating in the 2D nature. However, studies to elucidate its fundamental electronic states have been largely limited because only tiny powdered crystals were available, hindering a precise investigation by spectroscopy such as angle-resolved photoemission spectroscopy (ARPES). Here we report the direct mapping of the band structure with a tiny (∼20 × 20 μm2) r-BS powder crystal by utilizing microfocused ARPES. We found that r-BS is a p-type semiconductor with a band gap of >0.5 eV characterized by the anisotropic in-plane effective mass. The present results demonstrate the high applicability of micro-ARPES to tiny powder crystals and widen an opportunity to access the yet-unexplored electronic states of various novel materials.
Attempts were made at a simple, rapid and precise determination of calcium bilirubinate in the gallstone by means of infrared spectroscopy. The KBr-disk method was adopted for this purpose, the absorbance being calculated according to the base-line method. Of a number of absorptions characteristic of calcium bilirubinate, the 1624cm-1 band was determined to be most suitable for the key band of this compound in view of its satisfactory intensity, perfect adherence to Beer-Lambert's law and little susceptivity to interference of coexisting substances. A calibration curve was established at this wave number using authentic calcium bilirubinate, which proved to be valid also for multi-component samples simulating gallstones. The concentration of calcium bilirubinate in gallstone specimens as determined by this method fell in between analytical data obtained by two chemical methods, assuring the accuracy of this spectroscopic method.
The properties of newly discovered polar ScFeO3 with magnetic ordering are examined using Ab initio calculations and symmetry mode analysis. The GGA+U calculation confirms the stability of polar R3c Phase in ScFeO3 and the pressure induced phase transition to non-polar Pnma phase. Octahedron tilting and structural properties as a function of applied pressure have been analyzed. The origin of polar phase is associated with instability of non-polar R-3c phase and group theory using the symmetry mode analysis has been applied to understand this instability as well as the spontaneous polarization of polar R3c phase. The magnetic phase transition shows G-type AFM ordering of Fe3+ ion within Goodenough-Kanamori theory and the possibility of magnetic spin structure has been analyzed by using energy analysis including spin canting possibility.
A magnetic structural unit with asymmetric geometry may be a source for symmetry-dependent unique phenomena such as the magnetoelectric effect. The authors report the discovery of ferroelectricity and a magnetic-field-induced sign reversal of ferroelectric polarization in Pb(TiO)Cu${}_{4}$(PO${}_{4}$)${}_{4}$, whose structure is characterized by a staggered array of Cu${}_{4}$O${}_{12}$ magnetic units with convex geometry known as square cupola. Their model and first-principles calculations reveal that the observed complex magnetoelectric behavior originates from an exchange striction, where leading exchange interactions between spins play a crucial role. This result demonstrates that materials with convex-shaped magnetic structural units deserve to be explored to achieve strong magnetoelectric couplings.
