A paramagnetic salt is composed of 1 mole of noninteracting ions, each with a magnetic moment of one Bohr magneton (μB=9.274×10−24 joules/tesla). A magnetic field Be is applied along a particular direction; the permissible states of the ionic moments are either parallel or antiparallel to this direction.
a) Assuming the system is maintained at a temperature T=4 K and Be is increased from 1 Tesla to 10 Tesla, what is the magnitude of the heat transfer from the thermal reservoir?
b) If the system is now thermally isolated and the applied magnetic field Be is decreased from 10 Tesla to 1 Tesla, what is the final temperature of the system? (This process is referred to as cooling by adiabatic demagnetization.)