Magnetic properties of Mg1-pMnpTe2 near p = 0.5

Precise magnetization measurements and neutron diffraction measurements are carried out for Mg_1-pMn_pTe₂ near the critical concentration p = 0.5 for the antiferromagnetic ordering. A magnetization property which is similar to micto-magnetism is observed for p = 0.35 and p = 0.45 samples. The susceptibility shows an anomaly at T_f and field-cooling effect is notable below T_f. Neutron diffraction experiments show that most of the manganese moments are ordered antiferromagnetically for p = 0.53 while small fractions of Mn²⁺ are ordered for p = 0.45 and p = 0.35.     

Fast chemisorption of NO and SO2 on FeOOH crystals

The electrical conductivity changes of α-, β- and γ-FeOOH by adsorption of NO and SO₂ during 1 ms-1 min were determined. The conductivity change consists of fast and slow processes which are presumably caused by fast chemisorption on the oxygen vacancies and by slow one on the surface anions. The rate constants of fast and slow chemisorption were determined from the conductivity changes. The correlations of the rate constants with the compression pressure of specimen, adsorption temperature and original electrical conductivity are given. The order of magnitude of the fast chemisorption rate constants of the three polymorphs is related to the difference in the surface structure.     

Hybrid organic-inorganic conductor with a magnetic chain anion: kappa-BETS2[Fe(III)(C2O4)Cl2] [BETS = bis(ethylenedithio)tetraselenafulvalene

The synthesis, crystal structure, and electrical, optical, and magnetic properties of kappa-BETS2[Fe(III)(C2O4)Cl2], where BETS is bis(ethylenedithio)tetraselenafulvalene, are reported. The black plate crystals consist of parallel donor layers, two per unit cell, displaying a kappa-type packing of BETS(0.5+) within the bc plane and anionic magnetic chains, [Fe(C2O4)Cl2-]n, running along the c axis. It displays metallic behavior down to 4.2 K, and analysis of the optical reflectivity data gives unscreened plasma energies of 0.69 eV (E parallel c) and 0.40 eV (E perpendicular c). The optical anisotropy is larger than that seen for other kappa phases and is described well by transfer integrals obtained from extended Hückel calculations. However, the transfer integrals need to be scaled down uniformly by a factor of 1.21 to reproduce the absolute experimental plasma frequencies. The band structure consists of a one-dimensional (1D) band and a hole pocket, characteristics of kappa phases. The magnetic properties were modeled by the sum of a 1D antiferromagnetic chain contribution from the d spins of Fe3+, a temperature-independent paramagnetic contribution, and a Curie impurity term. At 4.5 K, there is a signature of long-range magnetic ordering to a canted-antiferromagnetic state in the zero-field-cooled-field-cooled magnetizations, and at 2 K, a small hysteresis loop is observed.     

Metal-organic frameworks from homometallic chains of nickel(II) and 1,4-cyclohexanedicarboxylate connectors: ferrimagnet-ferromagnet transformation

The hydrothermal reactions of nickel(II) nitrate with a mixture of the geometric cis and trans isomers of 1,4-cyclohexanedicarboxylic acid (1,4-chdc or C6H10(COOH)2) and a base yield three structurally different complexes, [Ni3(mu3-OH)2(mu4-cis-1,4-chdc)2(H2O)4].2H2O (1), [Ni(3)(mu3-OH)2(mu4-trans-1,4-chdc)2(H2O)4].4H2O (2), and [Ni(H2O)4(mu2-trans-1,4-chdc)], depending on the reaction conditions. The single-crystal X-ray structure analyses of 1 and 2 reveal segregation of the isomers and formation of frameworks based on infinite Ni3(OH)2(H2O)4 chains, acting as secondary building units, connected by either cis- or trans-chdc for 1 and 2, respectively. The frameworks sustain channels that house two or four water molecules, respectively, according to the size and shape of the channels that depend on the particular isomer. The structure of 3 consists of chains of square-planar Ni(H2O)4 bridged by trans-chdc. Magnetic data as a function of temperature and field of the virgin samples for 1 indicate long-range ordering (LRO) to a ferrimagnetic ground state at 2.1 K that is reversibly transformed into a ferromagnet below 4.4 K upon partial dehydration and rehydration. Powder X-ray diffraction of 1, in its virgin state, after dehydration and after rehydration, confirms the stability of the framework. The magnetic data for 2 tend toward a LRO state to possibly a ferrimagnet below 2 K. The temperature dependence of the susceptibility of the two compounds is accounted for by the presence of both ferro- and antiferromagnetic exchanges within each chain via Ni-O-Ni and Ni-O-C-O-Ni pathways and weak coupling between neighboring chains via the 1,4-chdc unit. 3 is a uniform s = 1 antiferromagnetic chain (J/kB = 2.27(1) K).     

Chemical modification of the internal surfaces of cylindrical pores of submicrometer size in poly(ethylene terephthalate)

Chemical modification of the internal surfaces of cylindrical pores with submicrometer pore diameter in a poly(ethylene terephthalate) (PET) film was examined. The modification involved the alkylation of the carboxylic acid on the surfaces with the alkylation reagent containing a fluorescent probe, and it was monitored by observing the change in fluorescent emission intensity. When the N,N-dimethylformamide solution of 4-(bromomethyl)-6,7-dimethoxycoumarin (BrCU), which bore a coumarin fluorophore, was introduced into the pores, the emission and excitation intensities of the membranes increased proportionally with increases of the pore surface areas. Fluorescent spots about 300 nm in diameter, which were located at the positions of the pores, can be observed in the fluorescence microscope image of the membranes, indicating that highly concentrated fluorescent probes are chemically incorporated on the internal surfaces of the cylindrical pores with 210 nm diameter in the membranes. In the reactions of the PET surfaces with BrCU, the fluorescent intensities increased with increases of the contact angles. This result indicates that the hydrophilicity of the internal pore surfaces can be qualitatively modified by controlling the change in the fluorescent intensities.     

Mesogenic and magnetic behavior in cobalt(II) and iron(II) compounds with long alkyl chains

Abstract  Metal complexes with long alkyl chains [Co(C16-terpy)₃](BF₄)₂ (1), [Fe(C16-terpy)₂](BF₄)₂ (2), [Co(C16-terpy)₂](BPh₄)₂ (3), [Co(C14-terpy)₂](BF₄)₂ (4), and [Fe(C12C10C5-terpy)₂](BF₄)₂ (5) were synthesized and their physical properties characterized, where C16-terpy, C14-terpy, and C12C10C5-terpy are 4′-hexadecyloxy-2,2′:6′,2′′-terpyridine, 4′-tetradecyloxy-2,2′:6′,2′′-terpyridine, and 4′-5′′′-decyl-1′′′-heptadecyloxy-2,2′:6′,2″-terpyridine, respectively. Complexes 1, 2, and 5 exhibited liquid–crystal properties in the temperature ranges of 371–528 K and 466–556 K, and 88–523 K, respectively. Variable-temperature magnetic susceptibility measurements revealed that the Co(II) complexes 1 and 4 exhibited unique spin transitions (T _1/2↓ = 217 K and T _1/2↑ = 260 K for 1 and T _1/2↓ = 250 K and T _1/2↑ = 307 K for 4), so-called ‘reverse spin transition,’ induced by structural phase transitions. Complex 3 exhibited gradual spin-crossover behavior (T _1/2 = 160 K.), and complex 5 exhibited spin transitions (T _1/2↑ = 288 K and T _1/2↓ = 284 K) at the liquid crystal transition temperature. Compounds with multifunction, i.e., magnetic and liquid–crystal properties, are important in the development of molecular materials. Graphical Abstract  

Superprotonic solid solutions between CsHSO4 and CsH2PO4

Solid solutions of (CsHSO₄)_1 − x(CsH₂PO₄)_x (x = 0.25-0.75) were synthesized by mechanical milling method over a wide range of compositions. Superprotonic cubic phase was confirmed for all these samples between 293 and 420 K depending on its composition. These superprotonic phases have primitive cubic structure similar to that of CsH₂PO₄. The kinetic stability of the supercooled cubic phase depends both on the composition x and the humidity of surrounding atmosphere. The most stable composition of the cubic phase was found around x = 0.67 and could be maintained for several days even under ambient atmosphere. The ionic conductivities of these superprotonic phases reached 10^− 2–10^− 3 S∙cm^− 1 at 450 K. With increasing x the ionic conductivity at the superprotonic phase decreased continuously associated with the increase of the activation energy. These findings suggest that the average number of the hydrogen bonds between XO₄ (X = S, P) units plays an important role on the stability of the cubic phase and also on the conductivity.     

Development of modulating permanent magnet sextupole lens for focusing of pulsed cold neutrons

Modulating permanent magnet sextupole lens (PMSx) for focusing pulsed cold neutrons is under development. The synchronized modulation of its field gradient suppresses the chromatic aberration which arises from the Time Of Flight method. The strength of the magnetic field, the torque, and the rise of temperature during its operation are studied on a fabricated prototype. Experiments on focusing pulsed very cold neutrons (VCN) at ILL (Institute of Laue Langevin, France) were carried out and VCN with around λ=40 Å were focused by the PMSx at a focal length of about 0.5 m. The experimental results are presented in conjunction with the principle of the neutron focusing and the modulating method of the focal strength of permanent magnet lens with the double ring structure.