Nuclear magnetic ordering of 3He clusters in solid 4He

The nuclear magnetic ordering of 3He clusters of a size of about 200 A was investigated in the confining geometry of a matrix of solid hcp 4He by heat capacity measurements at 0.7≤T≤30 mK and in the pressure range 26.5≤p≤36.4 bars. Dependent on the applied pressure, solid and liquid phases in the clusters are in coexistence, and we observe the transition of the solid 3He phase into the magnetically ordered state at pressures far below the bulk 3He melting pressure. The ordering temperature is strongly dependent on the history of the sample. Moreover, we observe an additional linear contribution of unknown origin to the heat capacity. copyright 1996 The American Physical Society