A collection n of non-interacting spins s,, i=1, 2,.n, (s, =t1) is kept in an external magnetic field b at a temperature t. the hamiltonian of the system is h =

A collection N of non-interacting spins S,, i=1, 2,.N, (S, =t1) is kept in an external magnetic field B at a temperature T. The Hamiltonian of the system is H =LB,S,. What should be the minimum value of uB for which the mean value kT (5)