
290 The Principles of Thermodynamics
After having spelled out all these generalities, we now restrict ourselves to cases
where the susceptibility obeys the Curie law
χ
=
a
T
(see chapter 8 for a fuller discus-
sion). As shown there, all expressions can be explicitly worked out, and in particular
S(B
e
,T)=S(0,T) −
1
2
Va
B
2
e
T
2
(14.22)
The important consequence of this is that for paramagnetic substances, for which
a > 0,entropydecreases as the magnetic field is increased. From our general consid-
erations it then follows that cooling results upon adiabatic demagnetization.Before
discussing the magnitude of the various effects, let us note that another consequence ...