Density variation of the frustrated ferromagnetism in 2D solid 3He

We measured heat capacities of the second layer incommensurate (IC) solid 3He adsorbed on graphite preplated with monolayer 4He ( 3He/ 4He/gr) in a wide temperature range (0.3 ≤T≤ 80 mK). From the high temperature series expansion fitting, we obtained density dependences of the multiple spin exchange interactions inherent to this two-dimensional quantum solid. Compared with the earlier results for the 3He/ 3He/gr system, the magnitude of the effective two-spin exchange interaction is clearly smaller at the lowest densities, while it is nearly the same at the highest densities. We argue that this difference is caused by the different densities of the second layer IC solids in the two systems. We also show that the total spin-entropy changes deduced from the present heat capacity data are smaller than the expected value by about 18%. © 2009 Springer Science+Business Media, LLC.