Magnetic Properties of Liquid ³He below 3 m°K

Abstract

Features observed along the ³He melting curve in compressional cooling experiments have suggested that at least one and perhaps two phase changes take place in either the solid and/or the liquid ³He within the cell at temperatures below 3 m°K.¹ In experiments in which the cell pressure was recorded as a function of time during periods in which the rate of compression dV/dt was held constant, two unexpected features were reproducibly obtained on the resulting pressurization curve which were labeled the A and B transitions, respectively, by Osheroff et al. The A transition is characterized by a sudden decrease in the rate of cell pressurization dP/dt upon cooling by roughly a factor of two in magnitude, all within a pressure interval of less than 3 × 10⁻⁴ atm. A nearly equal but opposite change in dP/dt is observed upon warming at precisely the same pressure. The pressure at which the A transition occurs in zero magnetic field is 1.70 × 10⁻¹ atm above the cell pressure at 7 m°K, and P(A) is lowered by the application of magnetic fields by an amount roughly equal to −6.7 × 10⁻⁵ H ² atm/kG². The pressure P(A) corresponds to a temperature of about 2.7 m°K obtained by extrapolating the shifted melting curve of Johnson et al.^1,2 The B transition is characterized by a sudden drop in cell pressure by about 3 × 10⁻⁴ atm upon cooling and by a brief hesitation in the cell pressure as it decreases upon warming (B’ transition). The pressure P(B’) is reproducibly 1.89 × 10⁻¹ atm above the cell pressure at 7 m°K in zero magnetic field, and is shifted to higher pressures by the application of magnetic fields by an amount given roughly by ΔP = +2.02 × 10⁻³ H ² atm/kG².

Work supported in part by the National Science Foundation through Grant No. GP-24179 and the Advanced Research Projects Agency through the Cornell Materials Science Center.