ABSTRACT
Tm(3)Cu(4)Ge(4) crystallizes in the orthorhombic Gd(3)Cu(4)Ge(4)-type crystal structure (space group Immm) whereas Tm(3)Cu(4)Sn(4) crystallizes in a distorted variant of this structure (monoclinic space group C2/m). The compounds were studied by means of neutron diffraction, specific heat, electrical resistivity and magnetic measurements. Analysis of experimental data revealed the presence of an antiferromagnetic order below 2.8 K in both compounds. In Tm(3)Cu(4)Ge(4) the magnetic unit cell is doubled in respect to the crystal unit cell and the magnetic structure can be described by a propagation vector k = [0, 1/2, 0]. A larger magnetic unit cell was found in Tm(3)Cu(4)Sn(4), given by a propagation vector k = [1/2, 1/2, 0] (for simplicity the orthorhombic description is used for both the germanide and the stannide). Close to 2 K, in each compound an incommensurate antiferromagnetic order develops. This low-temperature magnetic phase is characterized by a propagation vector k = [1/4, 0, k(z)], where k(z) is close to 0.49 and 0.47 in Tm(3)Cu(4)Ge(4) and Tm(3)Cu(4)Sn(4), respectively. The antiferromagnetic phase transitions are clearly seen in the bulk magnetic and specific heat data of both compounds.
Subject(s)
Copper/chemistry , Germanium/chemistry , Magnetics , Models, Chemical , Strontium/chemistry , Thulium/chemistry , Crystallography, X-Ray , Electric Conductivity , Magnets/chemistry , Neutron Diffraction , Phase Transition , TemperatureABSTRACT
A polycrystalline sample of Tb(3)Cu(4)Si(4) was investigated by means of magnetometric, electrical resistivity, thermopower and heat capacity measurements. This paper also includes reanalyses of former neutron diffraction data. The compound crystallizes in a Gd(3)Cu(4)Ge(4)-type orthorhombic structure (Immm space group), in which the Tb ions occupy two inequivalent sites (2d and 4e). The bulk results indicate that these two magnetic sublattices order antiferromagnetically at different temperatures, in agreement with the neutron diffraction data.
ABSTRACT
The electronic structure of the tetragonal U(2)T(2)In (T = Ni, Rh, Pt) compounds in the paramagnetic phase were studied by x-ray photoelectron spectroscopy (XPS). Both valence band and core level spectra were analysed. The experimental data are compared with the calculations of the density of states using the tight-binding linear muffin-tin orbital method (TB-LMTO) and full-potential local-orbital full-relativistic method (FPLO). The calculated data reveal a dominant U 5f electron character for the states near the Fermi level E(F) with a small contribution from U 5d, Ni 3d, Rh 4d, Pt 5d and In 5p states. The XPS valence bands of these compounds are characterized by a sharp peak of the U 5f states near the Fermi level (E(F)) and broad peaks of the Ni 3d, Rh 4d and Pt 5d states at about 2.6, 3.2 and 4.0 eV below E(F), respectively. The small change in the position of the U 5f peak with respect to E(F) is -0.35 eV for T = Ni and -0.15 eV for T = Rh and Pt. A satellite between the Ni 2p(1/2) and Ni 2p(3/2) peaks is visible, suggesting that the Ni 3d band is not completely filled, and the existence of a small induced magnetic moment on the Ni atoms cannot be ruled out.
ABSTRACT
The autopsy samples of human aortic wall were investigated to determine the structure of the inorganic deposits formed at the onset of the mineralization process. The studies were concentrated on the material for which histochemical staining of randomly selected sections did not reveal the presence of minerals. The highly mineralized human media samples as well as broad spectrum of model compounds were investigated for comparative purposes. It was found that the inorganic phase at the onset of tunica media mineralization is composed of a few compounds including octacalcium phosphate as the predominant Ca-P compound, and a Mg-compound, probably magnesium carbonate or double/triple salts containing magnesium carbonate.