EXACT DIAGONALIZATION STUDY OF MAGNETIC-PROPERTIES AT FINITE TEMPERATURES IN THE T-J MODEL

The temperature and doping dependence of the magnetic proper-ties of the t-J model in a two-dimensional square lattice are studied by exactly diagonalizing the hamiltonian for a 10-site cluster with realistic parameter values. By examining the static and dynamic spin correlation functions, we find that the magnetic properties in the low doping region are mainly controlled by the exchange interaction, whereas in the high doping region the nature of the magnetic excitations is similar to the non-interacting case. The crossover between the two regious occurs around the doping 0.2. The calculated results of the uniform spin susceptibility and the dynamic spin correlation function are compared with the experimental ones.