Experimental Measurements of Short Spin Relaxation Times: High Temperature Relaxation Processes of Fe(+) In MgO

摘要

The spin-lattice relaxation time, T(1), for the ground state Kramers doublet of Fe(+) in MgO has been measured by pulse saturation in a fast TWT (traveling wave tube) x-band spectrometer. All the data from 10 to 23K are accurately described by an equation. From 1.2 to about 10K, the relaxation time is angular dependent and there is evidence for cross relaxation. The microwave absorption line is inhomogeneously broadened at 4.2K and is nearly Lorentzian at all temperatures. The observed line width has a relaxation induced component whose temperature dependence from 23.2 to 37K with H is accurately described. Bloch's equations give the ratio T(1)/T(2) 0.73. These measurements establish the existance of sharp electronic levels at about 150/cm and 310/cm above the ground state Kramers doublet on the basis of relaxation via two Orbach processes. The energy level separation is in partial agreement with the predictions of a point charge model of cubic MgO. The alrge reduction of octahedral crystal field parameters indicated by the experimental results is discussed. (Author)