Structural, electronic, and magnetic characteristics of Np 2Co 17

I. Halevy, A. Hen, I. Orion, E. Colineau, R. Eloirdi, J. C. Griveau, P. Gaczyński, F. Wilhelm, A. Rogalev, J. P. Sanchez, M. L. Winterrose, N. Magnani, A. B. Shick, R. Caciuffo

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11 Scopus citations

Abstract

A previously unknown neptunium-transition-metal binary compound Np 2Co 17 has been synthesized and characterized by means of powder x-ray diffraction, 237Np Mössbauer spectroscopy, superconducting-quantum-interference-device magnetometry, and x-ray magnetic circular dichroism (XMCD). The compound crystallizes in a Th 2Ni 17-type hexagonal structure with room-temperature lattice parameters a=8.3107(1)= Å and c=8.1058(1).Å Magnetization curves indicate the occurrence of ferromagnetic order below T C350 K. Mössbauer spectra suggest a Np3 + oxidation state and give an ordered moment of μ Np=1.57(4) μ B and μ Np=1.63(4) μ B for the Np atoms located, respectively, at the 2b and 2d crystallographic positions of the P6 3/mmc space group. Combining these values with a sum-rule analysis of the XMCD spectra measured at the neptunium M 4,5 absorption edges, one obtains the spin and orbital contributions to the site-averaged Np moment [μ S=-1.88(9) μ B, μ L=3.48(9) μ B]. The ratio between the expectation value of the magnetic-dipole moment and the spin magnetic moment (m mdS=+1.36) is positive as predicted for localized 5f electrons and lies between the values calculated in intermediate-coupling (IC) and jj approximations. The expectation value of the angular part of the spin-orbit-interaction operator is in excellent agreement with the IC estimate. The ordered moment averaged over the four inequivalent Co sites, as obtained from the saturation value of the magnetization, is μ Co1.6 μ B. The experimental results are discussed against the predictions of first-principles electronic-structure calculations based on the spin-polarized local-spin-density approximation plus the Hubbard interaction.

Original languageEnglish
Article number014434
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume85
Issue number1
DOIs
StatePublished - 30 Jan 2012

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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