Halevy, I. and Hen, A. and Orion, I. and Colineau, E. and Eloirdi, R. and Griveau, J.-C and Gaczyński, P. and Wilhelm, F. and Rogalev, A. and Sanchez, J.-P and Winterrose, M. L. and Magnani, N. and Shick, A. B. and Caciuffo, R. (2012) Structural, electronic, and magnetic characteristics of Np_2Co_(17). Physical Review B, 85 (1). Art. No. 014434. ISSN 1098-0121 http://resolver.caltech.edu/CaltechAUTHORS:20120229-085626181
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A previously unknown neptunium-transition-metal binary compound Np_2Co_(17) has been synthesized and characterized by means of powder x-ray diffraction, ^(237)Np 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 α=8.3107(1) Å and c=8.1058(1) Å. Magnetization curves indicate the occurrence of ferromagnetic order below T_C>350 K. Mössbauer spectra suggest a Np^(3+) 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_(md)/μS=+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_(Co)≃1.6 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.
|Additional Information:||© 2012 American Physical Society. Received 30 November 2011; revised manuscript received 11 January 2012; published 30 January 2012. We thank D. Bouëxière and G. Pagliosa for their technical support and G. H. Lander for help during the XMCD experiment at ESRF. The high-purity neptunium metal required for the fabrication of the sample was made available through a loan agreement between Lawrence Livermore National Laboratory (LLNL) and ITU in the frame of a collaboration involving LLNL, Los Alamos National Laboratory, and the US Department of Energy.A.H. acknowledges the European Commission for support in the frame of the Training and Mobility of Researchers program. The support from Czech Republic Grants No. GACR P204/10/0330, No. GAAV IAA100100912, and No. AV0Z10100520 is thankfully acknowledged.|
|Classification Code:||PACS: 75.25.-j, 76.80.+y, 71.20.Lp, 71.15.Mb|
|Official Citation:||Structural, electronic, and magnetic characteristics of Np2Co17 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, and R. Caciuffo Published 30 January 2012 (8 pages) 014434|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||29 Feb 2012 21:31|
|Last Modified:||26 Dec 2012 14:53|
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