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

62. A collection Nof non-interacting spins S;, 1=1,2,.., N, (S; =t1) is kept in an external magnetic field B at a temperature T. The Hamiltonian of the system is H -u BS. What should be the minimum value of for which the of uB kT mean value (S;) 2 (a)Nin2 (b) 2 In 2 (C)In 2 (d) N In 2