J. Phys. Soc. Jpn. 75S (2006) pp. 24-29  |Previous Article| |Next Article|  |Table of Contents|
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Proc. of 5th Int. Symposium on ASR-WYP-2005 – Advances in the Physics and Chemistry of Actinide Compounds –

Neutron Scattering Study on UTGa₅ and NpTGa₅

Naoto Metoki^1,2

Recent neutron scattering studies on UTGa₅(T: Ni, Pd, Pt) and NpTGa₅(T: Fe, Co, Ni, Rh, Pt) are reviewed. The variety of the magnetic ordering with A-, G-, C-, and ferromagnetic type of structure is characteristic of this iso-structural family. This variety reminds us orbital degree-of-freedom, which may play important role. A careful powder diffraction study reported the existence of the critical tetragonality of UGa₃ layer in UTGa₅ structure for the A- and G-type magnetic ordering. A theoretical study based on j–j coupling scheme proposed two different ground states with a possible orbital ordering. We found that the successive magnetic transition in NpRhGa₅ and NpNiGa₅ is the 5f electronic transition between the low- and high-moment state. A recent mean field study based on a doublet ground state and a singlet excited state revealed that the successive transition and the magnetic phase diagram of NpTGa₅ (T: Co, Rh, Ni) can be systematically understood, where the quadrupolar interaction plays a key role: A ferro- and antiferroquadrupolar ordering coexists with magnetic ordering in the high-moment ground state of NpRhGa₅ and NpNiGa₅, respectively. On the other hand, there is no clear explanation for the successive transition from band theory. Further total energy and band calculation studies are necessary. There might be some connection between these two extremal models. We need a new picture to describe itinerant many body f electron system, which takes the orbital degree-of-freedom into consideration to understand underlying physics.

URL: http://jpsj.ipap.jp/link?JPSJS/75S/24/
DOI: 10.1143/JPSJS.75S.24

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