## Abstract

A previously unknown neptunium-transition-metal binary compound Np _{2}Co _{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 _{2}Ni _{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 _{C}350 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 _{md}/μ _{S}=+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.

Original language | English |
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Article number | 014434 |

Journal | Physical Review B - Condensed Matter and Materials Physics |

Volume | 85 |

Issue number | 1 |

DOIs | |

State | Published - 30 Jan 2012 |

Externally published | Yes |

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