Magnetic Susceptibility of Heavy Fermion 3He-Bilayers
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A 3He bilayer film adsorbed on graphite preplated with a bilayer of solid 4He has recently been shown to be a new heavy fermion system that can be tuned towards a quantum critical point (QCP) by varying the 3He coverage. We report new measurements of the temperature dependence of the magnetic susceptibility of this system over the temperature range 0.3 to 300 mK. The magnetisation of the 3He film is measured using pulsed NMR at a frequency of 60 kHz, on a SQUID detector setup with an untuned input circuit. The signal sensitivity attainable with this setup enables us to collect high-precision data with reasonable acquisition times, despite the low surface area of the sample (2 m2) and the small liquid susceptibility. The detailed NMR response provides an essential diagnostic tool to precisely adjust the 4He preplating. On cooling, the magnetisation evolves from Curie-law, through a distinct Kondo-like maximum at a temperature T *, to a weakly rising magnetisation far below the Curie law. This behaviour signifies the formation of the heavy fermion state of the coupled 3He layers. As the 3He coverage is increased towards the putative QCP, T * is tuned to lower temperature. These preliminary observations demonstrate the power of the technique, confirm previous results obtained in a different sample cell by a different method, and pave the way for a detailed study close to the QCP.