Unable to write in log file ../../bases/logs/portalorg/logerror.txt Pesquisa | Portal Regional da BVS
Mostrar: 20 | 50 | 100
Resultados 1 - 4 de 4
Mais filtros

Base de dados
Intervalo de ano de publicação
Inorg Chem ; 51(19): 10193-202, 2012 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-22963342


Ln(Cu,Al,Ga)(13-x) (Ln = La-Pr, and Eu; x ~ 0.2) were synthesized by a combined Al/Ga flux. Single crystal X-ray and neutron diffraction experiments revealed that these compounds crystallize in the NaZn(13) structure-type (space group Fm3[overline]c) with lattice parameters of a ~ 12 Å, V ~ 1600 Å, and Z ~ 8. Our final neutron models led us to conclude that Cu is occupationally disordered on the 8b Wyckoff site while Cu, Al, and Ga are substitutionally disordered on the 96i Wyckoff site of this well-known structure-type. The magnetic susceptibility data show that Ce(Cu,Al,Ga)(13-x) and Pr(Cu,Al,Ga)(13-x) exhibit paramagnetic behavior down to the lowest temperatures measured while Eu(Cu,Al,Ga)(13-x) displays ferromagnetic behavior below 6 K. Eu(Cu,Al)(13-x) was prepared via arc-melting and orders ferromagnetically below 8 K. The magnetocaloric properties of Eu(Cu,Al,Ga)(13-x) and Eu(Cu,Al)(13-x) were measured and compared. Additionally, an enhanced value of the Sommerfeld coefficient (γ = 356 mJ/mol-K(2)) was determined for Pr(Cu,Al,Ga)(13-x). Herein, we present the synthesis, structural refinement details, and physical properties of Ln(Cu,Al,Ga)(13-x) (Ln = La-Pr, and Eu) and Eu(Cu,Al)(13-x).

Inorg Chem ; 51(2): 920-7, 2012 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-22206264


LnCu(2)(Al,Si)(5) (Ln = La and Ce) were synthesized and characterized. These compounds adopt the SrAu(2)Ga(5) structure type and crystallize in the tetragonal space group P4/mmm with unit cell dimensions of a ≈ 4.2 Å and c ≈ 7.9 Å. Herein, we report the structure as obtained from single crystal X-ray diffraction. Additionally, we report the magnetic susceptibility, magnetization, resistivity, and specific heat capacity data obtained for polycrystalline samples of LnCu(2)(Al,Si)(5) (Ln = La and Ce).

Phys Rev Lett ; 106(3): 037201, 2011 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-21405289


Magnetism in the orthorhombic metal CaFe(4)As(3) was examined through neutron diffraction for powder and single crystalline samples. Incommensurate [q(m) ≈ (0.37-0.39) × b*] and predominantly longitudinally (|| b) modulated order develops through a 2nd order phase transition at TN = 89.63(6) K with a 3D Heisenberg-like critical exponent ß = 0.365(6). A 1st order transition at T2 = 25.6(9) K is associated with the development of a transverse component, locking q(m) to 0.375(2)b*, and increasing the moments from 2.1(1) to 2.2(3) µ B for Fe2+ and from 1.3(3) to 2.4(4) µB for Fe+. The ab initio Fermi surface is consistent with a nesting instability in cross-linked FeAs strips.

Phys Rev Lett ; 104(21): 216405, 2010 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-20867124


Bad metal properties have motivated a description of the parent iron pnictides as correlated metals on the verge of Mott localization. What has been unclear is whether interactions can push these and related compounds to the Mott-insulating side of the phase diagram. Here we consider the iron oxychalcogenides La2O2Fe2O(Se,S)2, which contain an Fe square lattice with an expanded unit cell. We show theoretically that they contain enhanced correlation effects through band narrowing compared to LaOFeAs, and we provide experimental evidence that they are Mott insulators with moderate charge gaps. We also discuss the magnetic properties in terms of a Heisenberg model with frustrating J1-J2-J2' exchange interactions on a "doubled" checkerboard lattice.