Measurements on spin relaxation time in superfluid ${}_{}{}^3{}_{}{}^{}\mathit{A}_1^{}{}_{}{}^{}$ were carried out at a pressure of 22.4 bar and a static field of 7.5 kG. The influence of surface coverage by ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ was systematically explored. The ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ coverage is used to eliminate the spin relaxation at the boundary walls and to extract the spin relaxation time in the warmer half of bulk ${\mathit{A}}_1$ phase. The bulk spin relaxation time is much shorter than expected from Leggett-Takagi theory applied to the ${\mathit{A}}_1$ phase. In the colder half of the phase, ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ coverage anomalously has no effect on the spin relaxation time.

• Received 26 February 1992

DOI:https://doi.org/10.1103/PhysRevB.45.12616