Topics: Double ultrasonic dispersions due to rattling in SmOs4Sb12

Magnetic-Field-Independent Ultrasonic Dispersions due to Rattling in the Magnetically Robust Heavy Fermion System SmOs4Sb12
Tatsuya YANAGISAWA, Yoichi IKEDA, Hitoshi SAITO, Hiroyuki HIDAKA, Hiroshi AMITSUKA, Koji ARAKI, Mitsuhiro AKATSU, Yuichi NEMOTO, Terutaka GOTO, Pei-Chun HO, Ryan E. BAUMBACH, and M. Brian MAPLE

Elastic properties of the filled skutterudite compound SmOs4Sb12 have been investigated by ultrasonic measurements. The elastic constant C12(\omega) shows two ultrasonic dispersions at ∼15 K and ∼53 K for frequencies \omega between 33 and 316 MHz, which follow a Debye-type formula with Arrhenius-type temperature-dependent relaxation times, and remain unchanged even with applied magnetic fields up to 10 T. The corresponding activation energies were estimated to be E2 = 105 K and E1 = 409 K, respectively. The latter, E1, is the highest value reported so far in the Sb-based filled skutterudites. The presence of magnetically robust ultrasonic dispersions in SmOs4Sb12 implies a possibility that an emergence of a magnetically insensitive heavy fermion state in this system is associated with a novel local charge degree of freedom which causes the ultrasonic dispersion.

J. Phys. Soc. Jpn. 80 (2011) 043601.

(also available on cond-mat/1010.1387)

SmOs_4Sb_12 Ultrasonic Dispersion

Figures (a) Comparison of the ultrasonic dispersions that appear in elastic constant C11 of ROs4Sb12 (R = La-Sm) at several frequencies. Lower arrowheads with numbers 1 and 2 indicate the relaxation point \omega\taui ∼ 1 for i = 1 and 2, respectively. (\omega is ultrasonic frequency and \tau is relaxation time) The displayed data have been shifted to eliminate overlapping with each other and the SmOs4Sb12 data are magnified three times for the \Delta C11/C11-axis. (b) Arrhenius plots of the characteristic parameters of the ultrasonic dispersions (Attempt time: \tau0(i), Activation Energy: Ei) for ROs4Sb12 (R = La-Sm).

(*This research was performed at UC San Diego, Hokkaido University, and Niigata University in 2010.)

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3He-4He Dilution Fridge 3He-4He Dilution Refrigerator (Oxford Instruments)
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[TOPICS] EuIn2P2における磁場中比熱測定

図1 EuIn2P2の磁場中電気抵抗

EuIn2P2は六方晶 (空間群:P6(3)/mmc)の結晶構造を持ち,Tc = 24 Kにおいてキャントした強磁性秩序を起こす物質である.この物質の電気伝導や磁化測定は磁場効果を含めて研究されており,Tc近傍で巨大磁気抵抗を示すことが知られている.しかし,基本物性の一つである比熱測定は行われていなかった.そこで,EuIn2P2の熱特性を調べるために,試料作製および強磁場下における比熱測定を行った.その結果,強磁性転移は二次相転移であることやEuイオンのもつf電子は低温まで局在していることなどが熱特性の観点から確かめられた.磁場効果も強磁性体において期待されるものであり,強磁性転移が起きているという磁気測定の結果と一致した.

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to be published.

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