Heat capacity of thin films of He-3 adsorbed on a heterogeneous substrate

We have measured the heat capacity of He-3 films on porous Vycor glass at 10 less than or equal to T less than or equal to 600 mK. As the coverage is increased from 1 to 3 atomic layers, the heat capacity evolves from that typical to solid to that of liquid He-3, being weakly temperature dependent at thicknesses of about two layers. A model is proposed of a gradual ordering of spins in an amorphous He-3 film, suggesting a broad uniform distribution of the logarithm of exchange parameters. It yields a constant heat capacity of about 13 mu J/K m(2), which is close to the experimental results for He-3 films on silver and Vycor.