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

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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