Low-temperature magnetic properties of NpNi5

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.

HEN Amir;  COLINEAU Jennifer;  ELOIRDI Rachel;  GRIVEAU Jean-Christophe;  MAGNANI Nicola;  WILHELM F.;  ROGALEV A.;  SANCHEZ J.P.;  SHICK A.B.;  HALEVY Itzhak;  ORION I.;  CACIUFFO Roberto; 

2014-09-04

AMER PHYSICAL SOC

JRC91175

1098-0121,   

http://dx.doi.org/10.1103/PhysRevB.90.054408,    http://journals.aps.org/prb/abstract/10.1103/PhysRevB.90.054408,    https://publications.jrc.ec.europa.eu/repository/handle/JRC91175,   

10.1103/PhysRevB.90.054408,