Adiabatic demagnetization in a rotating frame (ADRF) has been realized by means of rf-electric-field excitation. The experiments were carried out in the double quantum transition of the ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ nuclear-spin system in ${\mathrm{Al}}_2$${\mathrm{O}}_3$. The excitation was caused by the time-dependent electric quadrupole interaction induced by the rf electric field. Although a strong rf electric field with an intensity of about 14 kV/cm was applied, the transverse field due to the rf electric field was so small that its role as a heat reservoir could be neglected. The observed ADRF processes and the irreversibility are analyzed in detail with use of Provotorov’s saturation theory and by consideration of the spin thermodynamics. The ADRF processes are well described by equations that we have derived from Provotorov’s saturation theory. This theoretical treatment is also applicable to the ADRF performed with use of an rf magnetic field under similar experimental conditions.

• Received 20 July 1992

DOI:https://doi.org/10.1103/PhysRevB.47.3213