Negative thermal expansion and antiferromagnetism in the actinide oxypnictide NpFeAsO

T. Klimczuk*, H. C. Walker, R. Springell, A. B. Shick, A. H. Hill, P. Gaczynski, K. Gofryk, S. A. J. Kimber, C. Ritter, E. Colineau, J. -C. Griveau, D. Bouexiere, R. Eloirdi, R. J. Cava, R. Caciuffo

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

32 Citations (Scopus)


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 T-N = 57 K is suggested by anomalies in the temperature-dependent magnetic susceptibility, electrical resistivity, Hall coefficient, and specific-heat curves. Below T-N, powder neutron diffraction measurements reveal an antiferromagnetic structure of the Np sublattice, with an ordered magnetic moment of 1.70 +/- 0.07 mu(B) aligned along the crystallographic c axis. No magnetic order has been observed on the Fe sublattice, setting an upper limit of about 0.3 mu(B) for the ordered magnetic moment on the iron. High-resolution x-ray powder diffraction measurements exclude the occurrence of lattice transformations down to 5 K, 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 T-N, 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.

Original languageEnglish
Article number174506
Number of pages10
JournalPhysical Review B: Condensed Matter and Materials Physics
Issue number17
Publication statusPublished - 9 May 2012


  • NPO2


Dive into the research topics of 'Negative thermal expansion and antiferromagnetism in the actinide oxypnictide NpFeAsO'. Together they form a unique fingerprint.

Cite this