Low temperature magnetic properties of NpNi$_5$
Authors:
A. Hen,
E. Colineau,
R. Eloirdi,
J. -C. Griveau,
N. Magnani,
F. Wilhelm,
A. Rogalev,
J. -P. Sanchez,
A. B. Shick,
I. Halevy,
I. Orion,
R. Caciuffo
Abstract:
We present the result of an extended experimental characterization of the hexagonal intermetallic Haucke compound NpNi$_{5}$. By combining macroscopic and shell-specific techniques, we determine the 5$f$-shell occupation number $n_f$ close to 4 for the Np ions, together with orbital and spin components of the ordered moment in the ferromagnetic phase below T$_C$ = 16 K ($μ_{S}$ = -1.88~$μ_{B}$ and…
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We present the result of an extended experimental characterization of the hexagonal intermetallic Haucke compound NpNi$_{5}$. By combining macroscopic and shell-specific techniques, we determine the 5$f$-shell occupation number $n_f$ close to 4 for the Np ions, together with orbital and spin components of the ordered moment in the ferromagnetic phase below T$_C$ = 16 K ($μ_{S}$ = -1.88~$μ_{B}$ and $μ_{L}$ = 3.91~$μ_{B}$). 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 quasi-triplet ground state. The ratio between the expectation value of the magnetic dipole operator and the spin magnetic moment ($3\langle T_{z}\rangle/ \langle S_{z}\rangle$ = +1.43) is positive and large, suggesting a localized character of the 5$f$ electrons. The angular part of the spin-orbit coupling ($\langle\vec{\ell}\cdot\vec{s}\rangle$ = -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.
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Submitted 25 July, 2014;
originally announced July 2014.