Magnetic Domain Structure of U2D2 Solid 3He by Using the Magnetic Resonance Imaging

A spatial distribution of the magnetic domain structure in the U2D2 phase of solid 3 He was examined by a special Magnetic Resonance Imaging (MRI) technique. There were three kinds of magnetic domains in a single seed crystal of a few mm^ 3 size and each domain size was as large as the seed crystal size. We investigated by MRI the distribution and growth process of domains in the following two ways. First, we observed how the domains evolved from pre-existing domains as the crystal grew in a long vertical sample cell. When the crystal became long enough, one or two domains from the three were selected at the upper part of the cell. Our analyses of domain walls show that the (110)a or (110)b, proposed by Tsubota et al., is consisted with our observation. The pre-existing domains grow in the fixed directions of the domain walls and neither the solid-liquid interface nor the solid-cell wall boundary control the domain distribution during the crystal growth. Second, we observed how the domains were formed when a crystal made a transition from the high field phase (HFP) to the U2D2 phase by a magnetic field cycling. After the magnetic field cycling, the original domain distribution reappeared with slight modifications, particularly near the solid-liquid interface. Possible causes of this memory effect are discussed.