NMR investigation of the magnetic susceptibility anisotropy in the a phase of 3He

• Main Author: Haley, Richard P
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1995
• Subjects: Applied physics; Atomic physics
• ISBN: 0355609010; 9780355609011

The anisotropy in the magnetic susceptibility of [3]He-A has been investigated using continuous wave tranverse NMR. This has been achieved by implementing a geometry where the NMR modes are influenced by the anisotropy. The anisotropy is defined as α = (χ⊥ - χ∥)/χ⊥ where χ∥ and χ⊥ are the susceptibilities for the spin space vector d perpendicular and parallel to the applied external dc magnetic field H. The experimental cell is constructed so that the helium sample is separated by mylar foils into layers 12 μm thick, perpendicular to H. This means that the orbital vector l is constrained to be parallel to the applied field. In low fields d is held parallel to l due to the dipole interaction. In this regime the NMR mode frequencies yield values for α and ΩA, the A phase longitudinal frequency. The magnitude and temperature dependence of α have been found to agree with theoretical prediction, and have been used to determine the Landau Fermi liquid parameter F[a0] . Above a critical field value, the dipole unlocking field, the d vector switches to perpendicular to H as the dipole interaction is exceeded by the free energy contribution due to the susceptibility anisotropy. Above this critical field we observe the expected negative frequency shift from the Larmor frequency, from which Ω[A] can be found independently of α. All measurements were made at a pressure of 29.34 bar.