Angle-dependent magnetoresistance oscillations and Fermi surface reordering at high magnetic fields is α-(ET)2KHg(SCN)4

Angle dependent magnetoresistance oscillations (AMRO) have been studied in the charge transfer salt α-(ET)₂KHg(SCN)₄ for magnetic fields in the range 0 - 30T. This salt exhibits the onset of antiferromagnetic order at temperatures T_N 8-10 K and the presence below this temperature of a region of sharp negative magnetoresistance at a field around 22 T known as the 'kink'. AMRO have been measured in this salt for a wide range of applied fields since the period, amplitude, and nature of the oscillations can be used to directly infer the character of the Fermi surface (FS) as a function of field. The data indicate that a profound change in the band structure occurs at this kink transition; the high field phase is characterised by quasi-2D oscillations from a closed cylindrical FS which is elongated in the c direction; the low field phase appears to be a spin density wave groundstate, with a FS consisting of a sheet (which is quasi-1D in character and tilted at an angle of 21° to the b^*c plane) and small closed 2D pockets. It is suggested that the breakdown orbits between the pockets and the 1D sheets are able to account for the various Shubnikov-de Haas frequencies observed below the kink.     

[Fe3(HCOO)6]: A Permanent Porous Diamond Framework Displaying H2/N2 Adsorption,Guest Inclusion,and Guest‐Dependent Magnetism

The porous magnet [Fe₃(HCOO)₆], the iron member of the [M₃(HCOO)₆] family (where M = Mn, Fe, Co, Ni, etc.), based on a diamond framework consisting of Fe‐centered FeFe₄ tetrahedral nodes, is prepared successfully by using a solution‐chemistry method. The as‐prepared compound, [Fe₃(HCOO)₆](CH₃OH)_1.5(H₂O)_0.5 ( 1 ‐ parent ), exhibits facile removal of its guests, methanol, and water, to give the desolvated framework [Fe₃(HCOO)₆] ( 2 ‐ empty ) that displays permanent porosity and thermal stability up to 270 °C. The flexibility of the framework and the amphiphilic nature of the surface of the pores consisting of both C–H and O arrays allows 2 ‐ empty to take up significant H₂ and N₂ at liquid‐nitrogen temperatures and a wide spectrum of both polar and nonpolar guests of different sizes. A series of guest‐inclusion compounds, [Fe₃(HCOO)₆](I₂)_0.84 ( 3 ‐ iodine ), [Fe₃(HCOO)₆](C₄H₈O) ( 4 ‐ THF ), [Fe₃(HCOO)₆](C₄H₄O) ( 5 ‐ furan ), [Fe₃(HCOO)₆](C₆H₆) ( 6 ‐ benzene ), [Fe₃(HCOO)₆](CH₃CN) ( 7 ‐ acetonitrile ), and [Fe₃(HCOO)₆]((CH₃)₂CO) ( 8 ‐ acetone ) are successfully prepared by vapor diffusion of the guest into the pores of 2 ‐ empty and their structures are characterized by using single‐crystal X‐ray crystallography. Zigzag molecular arrays of the guest are formed in the confined channels of the host framework, and the weak hydrogen‐bonding provides the main host–guest interaction. All the compounds show 3D long‐range magnetic ordering and guest‐modulated Curie temperatures, coercive fields, and remnant magnetization as a consequence of the subtle rearrangement of the magnetic framework that conforms to the size of the guests and the difference in host–guest interactions. A possible magnetic structure of the framework is proposed to account for magnetic competition and geometrical frustration. The thermal and spectroscopic properties of the compounds are also reported.     

De Haas-van Alphen oscillations near Bc2 in the organic superconductor κ-(ET)2Cu(NCS)2

We report a study of the de Haas-van Alphen effect near the upper critical field in the organic superconductor κ-(ET)₂Cu(NCS)₂. The experiments have been carried out for a range of sample orientations with respect to the magnetic field and of temperatures down to 20 mK. On entering the vortex state, an attenuation of the dHvA signal is observed relative to an extrapolation of the standard Lifshitz-Kosevich formula using band parameters measured in the normal state.     

Categorization Constructionist Assessment with Software-Based Affinity Diagramming

Affinity diagramming is a cheap and widely used knowledge elicitation technique in human–computer interaction (HCI). However, empirical methods for evaluating user performance in conducting affinity diagrams have remained relatively static. Despite the fact that often the main value of such affinity diagramming sessions lies in the group-based discussions and debates that take place during their construction, what is being captured is often only the final categorizations (the affinity diagram) rather than the process of constructing them. In this article, we propose the concept of categorization constructionism, which we describe as optimized when affinity diagrams are facilitated in groups that have a considerate input of activity in categorization decision-making. We describe how we used this rule to model the temporal nature found within affinity diagram categorizations as they are constructed. To help us test our approach, we utilized participatory design (PD) sessions in developing three TabletPC-based software tools (CATERINE, SAW, and MATE) that would record, allow manipulation of, and evaluate the organization of affinity constructs over time programmatically with digital inking processes. We then used these tools to conduct an experiment that would explore our concept of measuring constructionistic activity over time in practice through the use of our tools.     

Novel BEDT-TTF salts with magnetic anions [MoOCl4(H2O)] and [Re2(NCS)10]

We report two novel BEDT-TTF salts containing magnetic transition metal anions. Both compounds are unusual in not containing discrete layers of anions and cations. In (BEDT-TTF)[MoOCl₄(H₂O)] the anions form hydrogen-bonded chains that lie in between 1-dimensional ribbons of edge-linked BEDT-TTF molecules. The compound is semiconducting with σ₃00K 0.5Scm^{− 1} E_A0.leV. In (BEDT-TTF)₃[Re₂(NCS)₁₀] CH₂Cl₂ no continuous network of BEDT-TTF exists, however π-π interactions are seen between the cation and the [Re₂(NCS)₁₀]^{3 −} anion. The compound is semiconducting with σ300K 0.01Scm⁻¹; E_A = 0.30eV.     

Fermi surface studies of the pressure induced organic superconductor (ET)3Cl2.2H2O

The effects of temperature, pressure and magnetic field on the electrical transport of single crystal of (ET)₃Cl₂.2H₂O are reported. Increasing pressure gradually reduces the ordering temperature of a charge density wave ground state from 160 K at 1 bar to 6 K at 10.2 kbar. A superconducting state with T_c > 4 K is stabilised between 10.2 kbar and 13.5 kbar. Above 12.5 kbar, the observation of Shubnikov-de Haas oscillations allows the pressure dependences of the area of a closed Fermi surface pocket and the associated carrier effective mass to be deduced.     

Pressure and temperature dependence of the structural properties of the molecular semiconducting salt: α′-(BEDT-TTF)2Ag(CN)2

The temperature and pressure dependence of the electrical conductivity of the α′-(BEDT-TTF)₂Ag(CN)₂ salt shows a transition between two semiconducting phases at a critical temperature depending on pressure. This transition is crystallographically characterized by the appearance of a superstructure corresponding to the doubling of the b parameter. We present and discuss here the parameters evolution at decreasing temperature and increasing pressure and the structural evolution under constraints.