Direct, Orbach, and Raman Relaxation in Dilute Cerous Magnesium Nitrate

Paramagnetic-relaxation measurements are reported for Ce³⁺ present as a dilute impurity in La₂{Mg}₃(NO₃)₁₂·{}24H₂O. Intrinsic direct relaxation rates are observed at Zeeman frequencies low enough to avoid a phonon bottleneck. At higher frequencies, where a substantial bottleneck is present, the intrinsic direct rate is obtained by a special technique. Direct and Raman rates obey the expected frequency and temperature variations, and the Orbach process depends on Zeeman frequency in a way we ascribe to a phonon bottleneck at the Orbach frequency. We find T₁^-1=6.02×10^-39ν⁴T+0.09T⁹+exp(logB-ΔT), where ν is the Zeeman frequency in cps and T the temperature. The argument of the Orbach rate depends on Zeeman frequency. All of the parameters are found to agree well with the accepted theoretical model.