The mean field entropy for an ensemble of identical spins with arbitrary magnitude

This paper provides general mean field calculations of the entropy for an ensemble of N magnetic moments with an arbitrary spin value. Expressions for the case with an external magnetic field have been known for many years and have usually been calculated using the canonical ensemble partition function. Less well‐known calculations in the microcanonical ensemble are also demonstrated in this paper; they involve the method of Lagrange multipliers. In addition, various special cases and relevant approximations are discussed.