Epstein, Paul S. (1932) On ferromagnetism and related problems of the theory of electrons. Physical Review, 41 (1). pp. 91109. ISSN 0031899X. http://resolver.caltech.edu/CaltechAUTHORS:EPSpr32

PDF
See Usage Policy. 1965Kb 
Use this Persistent URL to link to this item: http://resolver.caltech.edu/CaltechAUTHORS:EPSpr32
Abstract
In this paper is presented a study of those electrons which hold together a chemically elementary crystal and are responsible for the homoeopolar bonds between neighboring atoms. The starting point of the theory is Slater's form of the secular equations for first order perturbations arising from the interactions of identical atoms composing a system. A rigorous solution of these equations is given in section 4. The investigation is carried through in a unified way for magnetic and nonmagnetic materials, with respect to internal energies and to magnetic properties. As anticipated by Heisenberg, the deciding factor is the sign of the Heitler and London interchange integral J1. Substances with large negative J1 are nonmagnetic, those with large positive J1, potentially ferromagnetic. For nonmagnetic bodies, the theory gives a confirmation of Bloch's conclusions with slight differences of interpretation. On the other hand, the results for magnetic materials are new and entirely different from Bloch's. As to specific heats, it is found that at very low temperatures they have the expression c=0.208 sR(T/θ)3/2, where R is the gas constant, s the number of valency electrons per atom, and θ has a close relation to the Curie point. With respect to ferromagnetism, the result is that a crystal satisfying Slater's equations is spontaneously magnetized almost to saturation but that the polarity of this magnetization changes its sense at irregular intervals. This fact suggests that ferromagnetic crystals must have a block structure and that they are coherent, in the sense of the validity of Slater s equations, only within the blocks (compare sections 10 and 11). With this hypothesis the theory accounts for the fundamental facts of ferromagnetism.
Item Type:  Article 

Additional Information:  ©1932 The American Physical Society. Received 20 May 1932. An abridgment of this paper was read before the National Academy of Sciences on April 26, 1932 at Washington, D.C. 
Issue or Number:  1 
Record Number:  CaltechAUTHORS:EPSpr32 
Persistent URL:  http://resolver.caltech.edu/CaltechAUTHORS:EPSpr32 
Alternative URL:  http://dx.doi.org/10.1103/PhysRev.41.91 
Usage Policy:  No commercial reproduction, distribution, display or performance rights in this work are provided. 
ID Code:  7084 
Collection:  CaltechAUTHORS 
Deposited By:  Tony Diaz 
Deposited On:  08 Jan 2007 
Last Modified:  26 Dec 2012 09:28 
Repository Staff Only: item control page