J. Romero de Paz

Structural characterization of Sm1−xCa1+xCrO4 (0≤x≤0.5) oxides

RCaCrO4 oxides, where R is a rare earth, crystallize in the distorted K2NiF4 structure with orthorhombic symmetry, space group Bmab. The increase of the Ca/R ratio induces a mixed valence in the chromium sublattice in the R1−xCa1+xCrO4 oxides. The evolution of the structure with the amount of x, is closely related to the decrease of the orthorhombic strain parameter which approaches zero for the sample with the higher Ca content Sm0.5Ca1.5CrO4 The non-stoichiometric Sm0.7Ca1.3CrO3.85 oxide has been obtained by reducing Sm0.7Ca1.3CrO4.20 under hydrogen-helium atmosphere. Both oxides have been characterized by thermal analysis and X-ray diffraction,

Magnetism of RCaCrO4 (R: Pr, Nd, Sm and Eu) oxides

Abstract SmCaCrO 4 and EuCaCrO 4 oxides have been characterized by means of X-ray powder diffraction and magnetization measurements. Both oxides present a distorted K 2 NiF 4 -type structure with orthorhombic symmetry, space group Bmab . The orthorhombic strain in the RCaCrO 4 (R: Pr–Eu) oxides increases with decreasing R 3+ ion size, taking the S o parameter values of 4.0×10 −3 and 13.3×10 −3 for praseodymium and europium compounds, respectively. Samarium and europium compounds show antiferromagnetic behavior on the chromium sublattice with an estimated T N of 150 and 160 K, respectively. The observed T Cr 3+ N variation in the RCaCrO 4 (R: Pr–Eu) oxides has been explained taking into account the competition between intra and interlayer magnetic interactions that take place in the CrO 2 layers of the structure. Concerning the rare earth sublattice, the Sm 3+ ions present antiferromagnetic order below 3 K while the Eu 3+ ions remain magnetically disordered because of their non-magnetic ground state.

Determination of the crystal and magnetic structure of the DyCrO4-scheelite polymorph by neutron diffraction

Neutron diffraction data of DyCrO4 oxide, prepared at 4 GPa and 833 K from the ambient pressure zircon-type, reveal that crystallize with the scheelite-type structure, space group I41/a. Accompanying this structural phase transition induced by pressure the magnetic properties change dramatically from ferromagnetism in the case of zircon to antiferromagnetism for the scheelite polymorph with a TN = 19 K. The analysis of the neutron diffraction data obtained at 1.2 K has been used to determine the magnetic structure of this DyCrO4-scheelite oxide which can be described with a k = [0, 0, 0] as propagation vector, where the Dy and Cr moments are lying in the ab-plane of the scheelite structure. The ordered magnetic moments are 10 μB and 1μB for Dy+3 and Cr+5 respectively.

Magnetic characterization of Pr2BaCuO5

The magnetic behaviour of Pr 2 BaCuO 5 oxide has been studied by means of magnetic susceptibility, magnetization, specific heat and neutron powder diffraction at low temperatures. This oxide behaves as an antiferromagnetic with a Neel temperature of 13.7 K and the magnetic structure can be described on the basis of a wavevector k = [0, 0, 0]. The Cu 2+ magnetic moments are aligned along the c-axis of the crystal structure, while the Pr 3+ magnetic moments lie in the ab-plane with a small component along the c-axis. The experimental values of the ordered moments at 2 K are 0.9(3) and 0.8(3) μB for copper and praseodymium ions, respectively. The obtained set of crystal field parameters reproduces the paramagnetic susceptibility measurements and justifies the low experimental ordered moment of the Pr 3+ ion.