SQUID磁束計による磁化測定
図1 Quantum Design社製MPMS
Quantum Design社製のMPMS(Magnetic property Measurement System) (図1) は取り扱いが簡便で測定感度が高い磁化測定装置です。 この装置は引き抜き法と呼ばれる方法を用いて磁化を求めています。引き抜き法とは図2のようなコイルの中で磁化した試料を引き抜きコイルに発生した誘導起電力を測定、フィッティングすることで磁化を求める方法です。コイルが上下と中心で逆向きになっていることで外部の磁場の干渉やノイズを除去することができます。 MPMSで測定できる温度は2~400 K、印加できる磁場は-5.5 T~5.5 Tです。また圧力セルを用いることで高圧下での磁化測定、回転機構を用いることで角度分解磁化測定といった測定も可能になります。|
図2 引き抜き法の概念図 |
図3 試料の位置に対する誘導起電力とフィッティング関数 |
X線を用いた物質評価
アーク炉やプラズマジェット炉で作製した試料をX線を用いて評価します。評価の手法はラウエ法、粉末ディフラクトメーター法、EPMA(Electron Probe Micro Analyzer)です。 ・ラウエ法 図1のようにX線を単結晶試料に当てて、散乱したX線でフィルムを感光させます。このときブラッグの反射条件を満たしてX線が強めあうと図2のように黒い斑点がフィルムに現れます。この斑点の対称性(4回対称、鏡映面等)は結晶の対称性を反映しているので結晶面の対称性、軸方向が分かります。|
図1 ラウエ法の概念図(背面反射法) |
図2 ラウエ写真の例 |
図3 粉末ディフラクトメーター法の概念図
・EPMA 試料に電子線を照射すると図5のような反応がおこります。この中の特性X線いうものは波長が原子によって決まっているX線です。電子線を照射したときに飛び出してくる特性X線の波長のスペクトルを調べることで電子線の当たった領域の構成元素と割合が分かります。
図4 電子線を試料に照射したときの反応
MPMS用ピストンシリンダーによる高圧下DC磁化測定
ドイツ・Braunschbeing工科大学Stefan Su(ウムラウト)llow 教授らによって開発されたDC磁化測定用の単層式ピストンシリンダーセル（Cu-Be合金製）です。市販のSQUID磁力計（MPMS, Quantum Design社）に取り付け可能となっており，理想的なSQUID電圧波形が得られるように非常に細長い構造になっています（全長～150 mm）。温度は2 K、圧力は約1 GPa（10000気圧）までの測定が可能です。
図1 MPMS用ピストンシリンダーセル概観
Topics: Double ultrasonic dispersions due to rattling in SmOs4Sb12
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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)
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.) |
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)
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.) |
