Nuclear magnetic properties of aluminium

We have demagnetized a 2.92 mole Al sample of 6 N purity and measured its nuclear specific heat at temperatures 21 μK≤T≤20 mK and in magnetic fields of 11.4 mT≤B≤69.0 mT. In addition, we have performed nuclear magnetic resonance experiments on it atT≤175 μK as well as on an Al powder and an AuAl₂ sample at 200 μK≤T≤22 mK. No anomalies could be detected in these temperature and field regions. This shows that Al is a good candidate for a nuclear demagnetization stage and that its nuclear specific heat can be used as a primary thermometer in the μK- and mK-temperature regimes. The NMR data indicate that the nuclear dipole-dipole interaction is dominant in Al. The absence of any anomalies in the spin lattice relaxation time τ₁ toT=34 μK indicates that a measurement of τ₁ also can be used for primary thermometry.