THE QUANTUM PHYSICS OF SOLIDS 



715 



not gain so much energy to shift from the more full to the less full 

 band. Hence at the higher temperature there is more decrease in 

 magnetization per degree rise in temperature than at the lower tem- 

 perature. A logical consequence of this reasoning is that the magnet- 

 ization decreases more and more rapidly as the temperature increases 



0.2 



TEMPERATURE, -r- 



ec 



Fig. 29 — Intrinsic magnetization versus temperature. The horizontal scale rep- 

 resents the temperature divided by the Curie temperature and the vertical scale, 

 the intrinsic magnetization divided by the intrinsic magnetization at absolute zero. 

 The theoretical curve is derived from quantum mechanics. 



and becomes zero at a certain critical temperature, which is known as 



the Curie temperature and denoted by dc. A more complete discussion 



of the theory of the temperature dependence of magnetism would 



belong in a paper devoted solely to the theory of magnetism.^* In 



38 See, for example, K. K. Darrow, Bell Sys. Tech. Jour. XV, 224 (1936), R. M. 

 Bozorth, "The Present Status of Ferromagnetic Theory," Bell Sys. Tech. Jour., XV, 

 63 (1936) and texts such as J. H. Van Vleck, "The Theory of Electric and Magnetic 

 Susceptibilities," Oxford, 1932, E. C. Stoner "Magnetism and Matter," Methuen and 

 Company, Ltd., London, 1934, and F. Bitter "Introduction to Ferromagnetism," 

 McGraw-Hill Book Co., New York, 1937. 



