Structural, electronic, and magnetic characteristics of Np2Co17

Article

关键词: RAY CIRCULAR-DICHROISM;    RARE-EARTH;    INTERMETALLIC COMPOUNDS;    MOSSBAUER-SPECTROSCOPY;    CRYSTAL-FIELD;    NEUTRON-SCATTERING;    SELF-ABSORPTION;    GROUND-STATE;    SYSTEM;    DIFFRACTION;   

DOI  :  10.1103/PhysRevB.85.014434

来源: SCIE

【 摘 要 】

A previously unknown neptunium-transition-metal binary compound Np2Co17 has been synthesized and characterized by means of powder x-ray diffraction, Np-237 Mossbauer spectroscopy, superconducting-quantum-interference-device magnetometry, and x-ray magnetic circular dichroism (XMCD). The compound crystallizes in a Th2Ni17-type hexagonal structure with room-temperature lattice parameters a = 8.3107(1) angstrom and c = 8.1058(1) angstrom. Magnetization curves indicate the occurrence of ferromagnetic order below T-C > 350 K. Mossbauer spectra suggest a Np3+ oxidation state and give an ordered moment of mu(Np) = 1.57(4) mu(B) and mu(Np) = 1.63(4) mu(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,M-5 absorption edges, one obtains the spin and orbital contributions to the site-averaged Np moment [mu(S) = -1.88(9) mu(B), mu(L) = 3.48(9) mu(B)]. The ratio between the expectation value of the magnetic-dipole moment and the spin magnetic moment (m(md)/mu(S) = +1.36) is positive as predicted for localized 5 f 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 mu(Co) similar or equal to 1.6 mu 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.

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