Ultrasonic Team (T. Yanagisawa, Hokkaido Univ,)    
Top > Publications


Topics: Discovery of Double Ultrasonic Dispersion due to Rattling in NdOs4Sb12

Jul 10, 2008

日本語解説 >> Topics「カゴ状化合物のラットリング

Ultrasonic investigation of the off-center rattling in the filled skutterudite compound NdOs4Sb12
Tatsuya Yanagisawa, Pei-Chun Ho, William M. Yuhasz, M. Brian Maple, Yuri Yasumoto, Hiromu Watanabe, Yuichi Nemoto, and Terutaka Goto

The off-center rattling of Nd rare-earth ions in the filled skutterudite compound NdOs4Sb12 has been investigated by ultrasonic measurement. The longitudinal C11 mode for frequencies between 34 and 253 MHz shows a marked frequency dependence in elastic constant and ultrasonic attenuations at two different temperatures centered at around 45 and 15 K. The relaxational frequency dependence of ultrasonic dispersion reveals a thermally activated Γ23-type off-center motion of Nd-ions, involving local charge fluctuations with Γ23 symmetry in the (OsSb3)4 cage. An attempt time τ0,(1)=7.5×10-12 s and an activation energy E1=337 K were obtained from fits to the dispersion at around 45 K. The presence of another dispersion at lower temperatures of around 15 K implies that the rattling in NdOs4Sb12 has an additional low-energy excitation characterized by a lower activation energy E2∼67 K with an attempt time τ0,(2)=5.1×10-11 s.

J. Phys. Soc. Jpn. 77 (2008) 074607.

NdOs_4Sb_12 Ultrasonic Dispersion

Figure (a) Relative change in elastic constant ΔC11/C11 as function of temperature at frequencies of 34, 108, 180, and 253 MHz. (b) Solid lines show calculations of ΔC11/C11 using Landau-Khalatnikov theory. Dotted lines indicate the higher-frequency limit of the elastic constant C and the low frequency limit C0. Arrows indicate the temperatures that satisfy the resonant condition of ω ∼ 1/τi. (c) Temperature dependence of ultrasonic attenuation coefficient α11 at frequencies of 34, 108, 180, and 253 MHz. Solid lines are theoretical fits using the parameters.

(*This research was performed at UC San Diego and Niigata University in 2006.)

Abstract

Apr 29, 2008
Thermodynamic and transport studies of the ferromagnetic filled skutterudite compound PrFe4As12
T. A. Sayles, W. M. Yuhasz, J. Paglione, T. Yanagisawa, J.R. Jeffries, M.B. Maple, Z. Henkie, A. Pietraszko, T. Cichorek, R. Wawryk, Y. Nemoto and T. Goto

A variety of thermodynamic and transport measurements were made on high-quality single crystals of the Pr-based filled skutterudite compound PrFe4As12. Abrupt features in magnetization, ac susceptibility, specific heat, resistivity, thermoelectric power, and ultrasonic velocity reveal the onset of long range ferromagnetic order below ThetaC=18 K. The low-temperature magnetic susceptibility is characterized by a Curie–Weiss law with an effective moment of 3.52µB/f.u. and a saturation magnetization of 2.3µB/f.u., which is consistent with a magnetic Γ5 triplet ground state. A gaplike reduction of the large electronic specific heat coefficient of 340 mJ/mol K2 and several other features point to a strongly correlated electron behavior that is likely coupled to a change in magnetic and/or structural order near T*~12 K. Furthermore, this complex magnetic state is found to be strongly field dependent, as evidenced by a change in the easy axis at low fields and an additional contribution to thermal conductivity appearing only at high fields.

Phys. Rev. B 77 (2008) 144432. (Editor's Suggested).

PrFe4As12 combinedfigure

Figure : A comparison of low-temperature specific heat, electrical resistivity, magnetization, ac susceptibility,
thermopower, and ultrasound data that are used to correlate features that are observed at the ferromagnetic ordering temperatureThetac = 18 K and the characteristic temperature T*= 12 K and T' = 10 K.

Upper: Temperature derivative of resistivity and electronic plus magnetic contributions to specific heat, which shows a striking resemblance of the temperature dependence of each throughout the entire range.

Middle: Low-field (5 mT) dc magnetization and the imaginary part of the ac susceptibility, highlighting the coincidence of both the irreversibility temperature in M(T) and the peak in Chi_ac(T) with T*.

Lower* Zero-field thermoelectric power and relative change in the elastic constant ΔC44/C44 as a function of temperature for PrFe4As12.

(* This research was performed at UC San Diego and Niigata University in 2006-2007)

Abstract

Mar 28, 2008
Ultrasonic investigation of field-dependent ordered phases in the filled skutterudite compound PrOs4As12
T. Yanagisawa, W. M. Yuhasz, T. A. Sayles, P. -C. Ho, M. B. Maple, H. Watanabe, Y. Yasumoto, Y. Nemoto, T. Goto, Z. Henkie and A. Pietraszko

Elastic constant measurements down to 0.48 K and in magnetic fields up to 11 T were performed on a single crystal of the filled skutterudite compound PrOs4As12. The longitudinal CL111=CB+4C44/3 mode shows Curie-type softening below ~25 K, which is explained in terms of the quadrupole susceptibility modified by a crystalline electric field with a Γ4(2) ground state. A detailed H-T phase diagram for H || [111] is compiled with the elastic anomalies, which appear on the boundaries of two ordered phases at temperatures below 2.3 K and in fields below 3 T. The intermediate phase between 2 and 2.5 T assumes the aspect of antiferroquadrupolar ordering.

Phys. Rev. B 77 (2008) 094435,

also on J. Phys. Soc. Jpn. 77 (2008) Suppl. A, pp. 225-228.

PrOs4As12_Phasediagram

Figure : Magnetic field vs. Temperature (H-T) phase diagram of PrOs4As12 with fields (a) H || [111] and (b) H || [1-10]. Data points are determined by a feature of elastic anomalies; upward or downward in CL111 vs. H (solid circles and squares), CL111 vs. T (open circles and squares); minimum in CL111 vs. H (times), CL111 vs. T (plus). Error bars on the markers indicate roughly estimated transition width. Solid lines are guides to the eyes, separating the PM region (phase I), AFM region (phase III) and unknown ordered phase II and II'.

(*This research was performed at Niigata University in 2007-2008.)

Abstract

Mar 22, 2005
Dilatometric measurements and multipole ordering in DyB2C2 and HoB2C2
Tatsuya Yanagisawa, Tatsuya Moriwaki, Terutaka Goto, Yuichi Nemoto, Shingo Miyata, Ryuta Watanuki, and Kazuya Suzuki

We have performed dilatometric measurements by the capacitance method on tetragonal rare earth compounds DyB2C2 and HoB2C2 that show antiferro-quadrupole (AFQ) ordering. The tetragonal structure is invariant across the paramagnetic phase to the AFQ phase at TQ=24.7 K in DyB2C2. In the case of intermediate phase IV of HoB2C2, between TC1=5.9 K and TC2=5.0 K, the lattice length along the [101] direction reveals an abrupt increase, while the lengths along the [100] and [110] directions shrink slightly. This lattice distortion is described in terms of triclinic strain εyz = εzx≠0 indicating the spontaneous ferro-quadrupole moment <Oyz>= <Ozx>≠0. A plausible model, based on an octupole ordering <Tx>=<Ty>=<Tz>≠0, in phase IV of HoB2C2, is argued.

J. Phys. Soc. Jpn. 74 (2005) 1666.

DyB_2C_2&HoB_2C_2

Figures: Relative change of thermal expansion ΔL=L as a function of temperature along the [100], [110], [101] and [001] directions of DyB2C2 and HoB2C2, normalized to their values at 35 K and 10 K, respectively.

(*This research was performed at Niigata University in 2004.)

Page 2/2: ‹ 前へ 1 2

VLTLab Home Page Syndicate this site (XML)

Contents  

Archives  

Today's Quotes

Kaleidoscope

<a href='https://phys.sci.hokudai.ac.jp/LABS/kyokutei/vlt/yanagisawa//Kaleidoscope/Chargedistribution_Symmetry.htm'>解説記事を読む...</a> ▶Read this article...

Fundings

Eco-inventry

path: publications