In adiabatic demagnetization, we use a magnetic ield to couple away almost all of the residual energy of a crystal that has been cooled to 2.2 K by liquid helium. (We can get below the normal boiling point of liquid helium by boiling it at lower pressure.) Use Einstein's molar energy of the crystal
in the low-temperature limit to estimate the residual molar energy of a crystal with an Einstein frequency of 105 cm-1 at 2.2 K. (he answer is smaller than you may expect.)