緩和法比熱測定

熱緩和法とは、試料に与えていた熱を切った際の試料温度の緩和現象から比熱を求める実験手法です。具体的には、試料の回りに精密に温度コントロール可能な熱浴T0を作り、試料と熱浴との間を比較的弱い熱伝導パス(熱伝導度KW)で結びます。(図1)試料部には小型の温度計とヒーターを装着し、このヒーターに通電する事で試料温度を熱浴よりΔT だけ高い定常状態で保持しておきます。その後、一気にヒーターを切ると熱伝導パスを通じて試料から熱浴に熱が逃げて行きます。この温度緩和過程は通常指数関数型になり、その時定数を解析する事により試料部の比熱を求めます。 この実験手法により、わずか数mg程度の小さな試料の比熱を広い温度範囲かつ強磁場中で測る事が出来ます。比熱からは物質のエントロピーを見積もる事ができて、系のもつ微視的自由度の振る舞いを予想できます。比熱は物質の性質を理解する上で最も重要な物理量のひとつです。我々の研究室では、
Heliox :0.36 [K] < T < 200 [K] 、 B < 12 [T] (図2)
PPMS :2 [K] < T < 380 [K] 、 B < 9 [T]    (図3)
これらの装置により比熱測定を行っています。図4にPPMSでの実際の測定結果を示します。

図1

図2

図3

図4


Category: Research | Static URL: /research/Heliox.htm|




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.)


Category: Research | Static URL: /research/SmOs4Sb12.htm|




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.)


Category: n/a | Static URL: /SmOs4Sb12.htm|



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Facilities

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Refrigerators

3He-4He Dilution Fridge 3He-4He Dilution Refrigerator (Oxford Instruments)
+ Superconducting Magnet 9 T
3He Fridge (Heliox) 3He Single-Shot Refrigerator (Heliox, Oxford Instruments)
+ Superconducting Magnet 12 T
3He Fridge (Heliox)  Secondary 3He Single-Shot Refrigerator (Heliox, Oxford Instruments) Secondary
Homemade Dilution Fridge Homemade Dilution Refrigerator (Gas-Handling System)
Homemade Dilution Fridge Homemade Dilution Refrigerator (Cryostat)
3He Gas Handling Sytem (Homemade) 3He Gas Handling System
Top Loading Probe for 3He Single Shot Top Loading Probe for 3He Single Shot Fridge
Metal Dewar with 8TSCM Metal Dewar with 8T SCM
6T SCM (Split Magnet) 6T SCM (Split Magnet)
Mini Fridge Top Loading 4He Mini-fridge
4He Fridge 4He Refrigerator

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Category: Research | Static URL: /research/facilities.htm|



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