脉冲磁场中磁致伸缩、介电常数和磁热效应的电容检测
Capacitive detection of magnetostriction, dielectric constant, and magneto-caloric effects in pulsed magnetic fields
摘要：
本文报道了一种电容测量系统的研制，该系统能在高达61 T的脉冲磁场中测量电容。通过使用该系统，可以在脉冲磁场条件下研究各种物理量的磁场响应，例如磁致伸缩、磁场诱导的复介电常数变化和磁热效应。在这里，我们检查我们的系统的有效性，这些磁场感应现象的脉冲磁铁的调查。对于磁致伸缩测量，样品的磁致伸缩可以通过粘合在样品上的两个对准的电极和磁致伸缩计之间的电容的变化来测量。我们证明了一个精确的检测谷极化半金属铋通过磁致伸缩信号的分辨率优于10 $^{-6}$的相对长度变化。对于磁场诱导的复介电常数的变化，我们成功地观察到明显的介电异常伴随着磁/磁电相变的多铁性Pb（TiO）Cu $_4$（PO $_4$）$_4$。对于磁热效应的测量，用由非磁性铁电化合物KTa $_{1-x}$ Nb $_x$ O $_3$（$x$ = 0.02）制成的电容温度计验证Gd $_3$ Ga $_5$ O $_{12}$的磁场诱导的样品温度变化，该电容温度计的电容几乎与场无关。这些结果表明，我们的电容测量系统是一个很有前途的工具，研究各种磁场感应现象，一直难以检测在脉冲磁场。
英文摘要：
We report on the development of a capacitance measuring system which allows measurements of capacitance in pulsed magnetic fields up to 61~T. By using this system, magnetic-field responses of various physical quantities such magnetostriction, magnetic-field-induced change in complex dielectric constant, and magneto-caloric effect can be investigated in pulsed-magnetic-field conditions. Here, we examine the validity of our system for investigations of these magnetic-field-induced phenomena in pulse magnets. For the magnetostriction measurement, magnetostriction of a specimen can be measured through a change in the capacitance between two aligned electrodes glued on the specimen and a dilatometer. We demonstrate a precise detection of valley polarization in semimetallic bismuth through a magnetostriction signal with a resolution better than 10$^{-6}$ of the relative length change. For the magnetic-field-induced change in complex dielectric constant, we successfully observed clear dielectric anomalies accompanied by magnetic/magnetoelectric phase transitions in multiferroic Pb(TiO)Cu$_4$(PO$_4$)$_4$. For the measurement of magneto-caloric effect, a magnetic-field-induced change in sample temperature was verified for Gd$_3$Ga$_5$O$_{12}$ with a capacitance thermometer made of a non-magnetic ferroelectric compound KTa$_{1-x}$Nb$_x$O$_3$ ($x$ = 0.02) whose capacitance is nearly field-independent. These results show that our capacitance measuring system is a promising tool to study various magnetic-field-induced phenomena which have been difficult to detect in pulsed magnetic fields.
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