Published online by Cambridge University Press: 24 October 2008
Ising discussed the following model of a ferromagnetic body: Assume N elementary magnets of moment μ to be arranged in a regular lattice; each of them is supposed to have only two possible orientations, which we call positive and negative. Assume further that there is an interaction energy U for each pair of neighbouring magnets of opposite direction. Further, there is an external magnetic field of magnitude H such as to produce an additional energy of − μH (+ μH) for each magnet with positive (negative) direction.
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† Cf. the preceding paper. This will be referred to as A.
* This value could be considerably improved without difficulty. Taking into account that according to condition (2) two successive steps must never be opposite to each other, there is only a choice of three possibilities for all but the first step, and in this way we easily obtain ⅓ instead of ¼.