Thermodynamics of Rh nuclear spins calculated by exact diagonalization

We have employed the method of exact diagonalization to obtain the full-ene rgy spectrum of a cluster of 16 Rh nuclear spins, having dipolar and RK int eractions between first and second nearest neighbours only. We have used th is to calculate the nuclear spin entropy, and our results at both positive and negative temperatures follow the second-order high-temperature series e xpansions for \T\ > 3 nK. Our findings do not agree with the measurements o f the former Rh experiment in Helsinki, where a deviation is seen at much h igher temperatures. (C) 2000 Elsevier Science B.V. All rights reserved.