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|Title:||Negative Thermal Expansion and Antiferromagnetism in the Actinide Oxypnictide NpFeAsO|
|Authors:||KLIMCZUK TOMASZ; WALKER H.c.; SPRINGELL R.; SHIK ALEXANDER; HILL A. H.; GACZYNSKI Piotr; GOFRYK Krzysztof; KIMBER S. A. J.; RITTER C.; COLINEAU Eric; GRIVEAU Jean-Christophe; BOUEXIERE Daniel; ELOIRDI Rachel; CAVA R. J.; CACIUFFO Roberto|
|Citation:||PHYSICAL REVIEW B vol. 85 no. 17 p. 174506-10|
|Publisher:||AMER PHYSICAL SOC|
|Type:||Articles in Journals|
|Abstract:||A neptunium analog of the LaFeAsO tetragonal layered compound has been synthesized and characterized by a variety of experimental techniques. The occurrence of long-range magnetic order below a critical temperature TN = 57 K is suggested by anomalies in the temperature-dependent magnetic susceptibility, electrical resistivity, Hall coefficient, and specific-heat curves. Below TN, powder neutron diffraction measurements reveal an antiferromagnetic structure of the Np sublattice, with an ordered magnetic moment of 1.70 ± 0.07μB aligned along the crystallographic c axis. No magnetic order has been observed on the Fe sublattice, setting an upper limit of about 0.3μB for the ordered magnetic moment on the iron. High-resolution x-ray powder diffraction measurements exclude the occurrence of lattice transformations down to 5K, in sharp contrast to the observation of a tetragonal-to-orthorhombic distortion in the rare-earth analogs, which has been associated with the stabilization of a spin-density wave on the iron sublattice. Instead, a significant expansion of the NpFeAsO lattice parameters is observed with decreasing temperature below TN, corresponding to a relative volume change of about 0.2% and to an Invar behavior between 5 and 20 K. First-principles electronic structure calculations based on the local spin density plus Coulomb interaction and the local density plus Hubbard-I approximations provide results in good agreement with the experimental findings.|
|JRC Institute:||Institute for Transuranium Elements|
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