## Abstract

We present the result of an extended experimental characterization of the hexagonal intermetallic Haucke compound NpNi5. By combining macroscopic and shell-specific techniques, we determine the 5f-shell occupation number nf close to 4 for the Np ions, together with orbital and spin components of the ordered moment in the ferromagnetic phase below TC=16 K (μS=-1.88 μB and μL=3.91 μB). The apparent coexistence of ordered and disordered phases observed in the Mössbauer spectra is explained in terms of slow relaxation between the components of a quasitriplet ground state. The ratio between the expectation value of the magnetic dipole operator and the spin magnetic moment (3Tz/Sz=+1.43) is positive and large, suggesting a localized character of the 5f electrons. The angular part of the spin-orbit coupling (- ·s- =-5.55) is close to the value of -6.25 calculated for trivalent Np ions in intermediate coupling approximation. The results are discussed against the prediction of first-principle electronic structure calculations based on the spin-polarized local spin density approximation plus Hubbard interaction, and of a mean field model taking into account crystal field and exchange interactions.

Original language | American English |
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Article number | 054408 |

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

Volume | 90 |

Issue number | 5 |

DOIs | |

State | Published - 11 Aug 2014 |

Externally published | Yes |