Pulsed Nuclear Magnetic Resonance on 3He Adsorbed on Bare and 4He Preplated MCM-41 Using DC SQUID Detection

Abstract

We report low field DC SQUID NMR measurements down to 1.5 K of 3He adsorbed in the pores of the mesoporous molecular sieve MCM-41. In the first experiment measurements were made on 3He adsorbed onto the bare pore walls of MCM-41 with coverages ranging from $n_{^{3}\mathrm{He}}=0.86n_{1}$ to full pores at $n_{^{3}\mathrm{He}}=1.79n_{1}$ , where n 1 is the coverage for monolayer completion. A second experiment was performed with low 3He coverages ( $n_{^{3}\mathrm{He}}\sim0.01n_{1}$ ) on 4He preplated pores, where a crossover to a quasi-1D state is expected to occur at temperatures sufficiently below 700 mK. In both experiments relaxation times T 1 and T 2 * were measured as a function of temperature and coverage at frequencies from 80 to 240 kHz. The frequency dependence of the linewidth in the pure 3He experiment is extremely weak therefore T 2 * ≈T 2. The 1.5 K isotherm shows a small minimum in T 2 * at a coverage corresponding to monolayer completion. In the experiment with 4He preplating there was no significant change in T 1 or T 2 * when the 3He coverage was doubled from $n_{^{3}\mathrm{He}}=0.01n_{1}$ to 0.02n 1 at a 4He preplating of $n_{^{4}\mathrm{He}}=1.05n_{1}$ . This suggests that the relaxation times are dominated by single particle effects in the low density regime.