Browsing by Author "Rodríguez-Velamazán, JA"

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    Magnetic structure and magnetocalorics of GdPO4
    (American Physical Society, 2014-10-21) Palacios, E; Rodríguez-Velamazán, JA; Evangelisti, M; McIntyre, GJ; Lorusso, G; Visser, D; de Jongh, LJ; Boatner, LA
    The magnetic ordering structure of GdPO 4 is determined at T=60 mK by the diffraction of hot neutrons with wavelength λ=0.4696 Å. It corresponds to a noncollinear antiferromagnetic arrangement of the Gd moments with propagation vector k=(1/2,0,1/2) . This arrangement is found to minimize the dipole-dipole interaction and the crystal-field anisotropy energy, the magnetic superexchange being much smaller. The intensity of the magnetic reflections decreases with increasing temperature and vanishes at T≈0.8 K, in agreement with the magnetic ordering temperature T N =0.77 K, as reported in previous works based on heat capacity and magnetic susceptibility measurements. The magnetocaloric parameters have been determined from heat capacity data at constant applied fields up to 7 T, as well as from isothermal magnetization data. The magnetocaloric effect, for a field change ΔB=0−7T , reaches −ΔS T =375.8mJ/cm 3 K −1 at T=2.1 K, largely exceeding the maximum values reported to date for Gd-based magnetic refrigerants.© 2014, American Physical Society.
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    Temperature- and pressure-dependent structural study of {Fe(pmd)2[Ag(CN)2]2}n spin-crossover compound by neutron laue diffraction
    (Wiley, 2014-06-04) Rodríguez-Velamazán, JA; Canadillas-Delgado, L; Castro, M; McIntyre, GJ; Real, JA
    The effect of pressure (up to 0.17 GPa) on the spin-crossover compound {Fe(pmd)2[Ag(CN)2]2}n [orthorhombic isomer (II), pmd = pyrimidine] has been investigated by temperature- and pressure-dependent neutron Laue diffraction and magnetometry. The cooperative high-spin [left right arrow] low-spin transition, centred at ca 180 K at ambient pressure, is shifted to higher temperatures as pressure is applied, showing a moderate sensitivity of the compound to pressure, since the spin transition is displaced by ca 140 K GPa-1. The space-group symmetry (orthorhombic Pccn) remains unchanged over the pressure-temperature (P-T) range studied. The main structural consequence of the high-spin to low-spin transition is the contraction of the distorted octahedral [FeN6] chromophores, being more marked in the axial positions (occupied by the pmd units), than in the equatorial positions (occupied by four [Ag(CN)2]- bridging ligands). © 1999-2020 John Wiley & Sons, Inc.