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論文

Magnetic phase diagram and Fermi surface properties of the heavy-fermion antiferromagnet UPd$$_{2}$$Cd$$_{20}$$

廣瀬 雄介; 土塔 寛*; 竹内 徹也*; 三宅 厚志*; 徳永 将史*; 仲村 愛*; 本間 佳哉*; 青木 大*; 本多 史憲*; 摂待 力生*

Journal of Physics; Condensed Matter, 38(24), p.245601_1 - 245601_11, 2026/06

https://doi.org/10.1088/1361-648X/ae72e0
 被引用回数：0 パーセンタイル：0.00(Physics, Condensed Matter)

The electronic state of UPd$$_{2}$$Cd$$_{20}$$, which exhibits a magnetic transition at $$T$$$$_{rm N}$$ $$sim$$ 5 K, is investigated by means of transport, high-field magnetization up to 55 T, specific heat in magnetic fields, and de Haas-van Alphen (dHvA) measurements, and compared with the non-5f compound ThPd$$_{2}$$Cd$$_{20}$$. A metamagnetic transition is observed at $$mu$$$$_{0}$$$$H_{rm c}$$ $$sim$$ 15-20 T, which continuously connects to $$T$$$$_{rm N}$$ in the H-T phase diagram. Although the magnetization reaches large values at high fields, the ordered magnetic moment is estimated to be small from small anomalies in specific heat at $$T$$$$_{rm N}$$ and in magnetization at $$T$$$$_{rm c}$$. The observed dHvA frequencies reveal enhanced cyclotron effective masses of 30 $$m_{0}$$, which are much heavier than those in ThPd$$_{2}$$Cd$$_{20}$$. These experimental results indicate that 5f-derived bands contribute to the large electronic specific heat coefficient of 670 mJ/mol K$$^{2}$$, demonstrating the dual localized-itinerant character of 5f electrons in UPd$$_{2}$$Cd$$_{20}$$.

論文

Experimental observation of 5f valence fluctuations by high-resolution X-ray absorption spectroscopy in UPd$$_{2}$$Cd$$_{20}$$

廣瀬 雄介; 本多 史憲*; 土塔 寛*; 河村 直己*; Kvashnina, K. O.*; Amidani, L.*; Uhl$'i$$v{r}$ov$'a$, K.*; Koloren$v{c}$, J.*; Havela, L.*

Physical Review B, 113(24), p.L241103_1 - L241103_6, 2026/06

https://doi.org/10.1103/g9y8-7lq9
 被引用回数：1 パーセンタイル：82.33(Materials Science, Multidisciplinary)

The regime of valence fluctuations, known from anomalous rare-earth systems with slow fluctuations between two different fn states, has not yet been identified by microscopic techniques at any Uranium compound. The reason may be in the predominant band character of U intermetallic compounds. Here we present U-L3 and M4 X-ray absorption spectra taken on UPd$$_{2}$$Cd$$_{20}$$, which is a heavy-Fermion antiferromagnet. Although it has only one type of U site, the spectra obtained in the High Energy Resolution Fluorescence Detection mode display two edges, each associated with different valence states, 5f2 and 5f3. This is strongly suggestive of slow f2 - f3 fluctuations on the timescale longer than the characteristic time of the spectroscopy technique. Unlike 4f systems in which such fluctuations lead to a destruction of magnetism due to involvement of one non-magnetic state, the f2 and f3 states in U are both possibly magnetic, allowing for the magnetic ordering in the fluctuating state. Such a new situation can bring more light into emergent phenomena observable in U systems at the verge of 5f localization.

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