Studies of Nuclear-Ordered Solid ^3He by using Ultrasonic Sound

由于导致固体^3He中核有序的主要相互作用是^3He原子之间的直接交换过程，因此核自旋系统与晶格强耦合。因此，同时利用核磁共振和超声方法研究核有序固体^3He是一个非常有趣的课题。在核有序化温度下，声速会发生变化，声速相对于磁各向异性轴会发生各向异性，由于磁声模和磁光模的共振吸收以及多重磁振子散射，声衰减也会发生变化。我们成功地制造了具有单磁畴的大型固体^3He单晶，并将其冷却到100 μ K的温度范围。本项目取得了以下成果：（1）核磁共振测量：对核有序^3He进行了低场脉冲核磁共振，研究了非线性自旋动力学。我们发现原子核的匀速运动 ...更多信息 r自旋在低温、低外加磁场和自旋从平衡位形大倾斜时变得不稳定。我们在自旋运动稳定的区域观察到多个自旋回波，可以研究相干偶极矩的详细形式。通过对磁振子热涨落的重正化，成功地解释了共振频率的微小负移。(2)晶体生长;为了生长出高质量的^3He单晶，我们研究了从超流^3He中生长出核有序固体^3He的晶体和熔化过程。我们发现晶体生长和熔化的速率是完全不同的。这种生长可能是由与螺位错有关的生长机制控制的，而熔体则是由类似于粗糙表面上^4He的机制控制的。(3)声学实验：搭建了声速和衰减测量系统。通过一次测量，我们对声速变化的分辨率为几ppm。我们完成了一个声室，研究了单畴和单畴晶体的核磁共振-声同步测量。少

Since the main interaction to cause the nuclear-ordering in solid ^3He is a direct exchange processes between ^3He atoms, the nuclear spin system is strongly coupled with a lattice. Therefore, it is very interesting to study nuclear-ordered solid ^3He by using both nuclear magnetic resonance and ultrasonic methods simultaneously. It is expected that there will be a change of the sound velocity at the nuclear-ordering temperature, anisotropy of the sound velocity against the magnetic anisotropy axis, and sound attenuation due to resonant absorption of the magnetic acoustic and optical modes and due to multiple magnon scattering.We succeeded in making a large single crystal of solid ^3He with a single magnetic domain and in cooling it to 100muK temperature range. We obtained the following results for this project :(1) NMR measurement ; We took pulsed NMR in the low field phase of the nuclear-ordered ^3He and studied the non-linear spin dynamics. We found that the uniform motion of nuclea … More r spin became unstable in low temperatutes, low applied fields and for a large tipping of spins from an equilibrium configuration. We observed multiple spin echoes in the regions where spin motion was stable and could study the detailed form of the coherent dipole torque. We succeeded in explaing the small negative shift of resonant frequency by renormalizing the thermal fluctuation of magnons.(2) Crystal growth ; In order to grow a single crystal of ^3He of good quality, we studied crystal growth and melt of nuclear-ordered solid ^3He from superfluid ^3He. We found that the rates of crystal growth and melt were quite different. The growth may be controlled by growth mechanisms related to the screw dislocation and the melt by mechanisms similar to ^4He on rough surfaces.(3) Sound experiment ; We constructed the sound velocity and attenuation measuring system. Our resolution of the change in sound velocity was several 10 ppm by one shot of measurement. We completed a sound cell to investigate the NMR-sound simultaneous measurement on a single and mono-domain crystal. Less