Phase transitions in quantum crystals : on growth of magnetically ordered 3He and a search for supersolid 4He

Abstract

Due to its rich magnetic phase diagram and its superfluidity, 3He is a very interesting system if magnetic effects on the crystal growth mechanisms want to be studied. Solid 3He orders magnetically into the U2D2 phase (an antiferromagnetic phase with two planes of spins pointing up and two planes of spins pointing down in sequence) when is cooled down to very low temperatures (below the N_el transition ~1mK). If the external magnetic field is increased above 450mT, the solid orders into a different magnetic phase, the so-called CNAF phase (a normal antiferromagnetic phase, but with the spins slightly tilted from their normal position with a significant magnetization). For first time a clear indication showing that external magnetic fields indeed affect the growth of the crystals was seen. Crystals in high magnetic fields grow almost ten times faster than crystals at zero magnetic field, which was completely unpredicted behavior. This results yield that the interface between the liquid and the solid and crystal lattice seem to couple strongly at high magnetic fields, while the coupling was weak at zero magnetic field.