Paramagnetic Relaxation and Crystal-Field Theory for the Ground Manifold of Chromium in Rutile

Abstract

Paramagnetic relaxation within the ground manifold of chromium in rutile is studied experimentally and theoretically. Relaxation proceeds solely by direct transitions between two Kramers doublets and, at low temperatures, approaches the behavior identified with the usual Orbach mechanism. The three characteristic decay times in this four-level system are expressed in terms of two temperature-independent parameters, which are evaluated from measurements of the longest two time constants. The decay times are independent of Zeeman field and chromium concentration and show the expected temperature variation. Strong-field crystalline-field theory is applied to the microwave spectrum and the relaxation process; theory explains the spectrum satisfactorily but is only marginally successful in explaining the behavior of the relaxation times.