
154 The Principles of Thermodynamics
later, superconductors are perfect diamagnets in the sense that B =0irrespective
of B
e
. In paramagnetic substances, with positive susceptibilities, just the opposite
happens. The induced magnetization actually enhances the external field, i.e B > B
e
.
For ferromagnetic substances, these considerations are not really applicable because
of the so called spontaneous magnetization because of which the magnetic system
may possess magnetization even in the absence of any external fields.
TABLE 8.1
Some magnetic materials and their magnetic susceptibility
χ
m
.
Name Type Temp(K)
χ
m
Water Dia. 300 -9.0·10
−6
Bismuth Dia. 300 -16.7 ...