Concentration Dependence of Spin-Lattice Relaxation Rates and Thermal Equilibrium in Ruby under High Magnetic Fields

Abstract

A chromium ion concentration dependence of spin-lattice relaxation in the chromium ion ground state ⁴A₂ in ruby (Al₂O₃; Cr³⁺) was measured in high magnetic fields from 69 KOe to 135 KOe. A critical Cr³⁺ concentration is found to be about 0.16%, above which the spin-lattice relaxation rates show a strong concentration dependence and the electron distribution in ⁴A₂, quartet spin states, is interpreted in terms of a single spin temperature. From these facts it is concluded that only in the high concentration region, energy transfers among single Cr³⁺ ions take place and electron spin states are in a thermal equilibrium.