Does the Jahn-Teller effect influence electron spin relaxation? Electron paramagnetic resonance and electron spin echo studies of the Mn2+ doped (NH4)2Mg(SO4) · 6H2O single crystal and comparison with Cu2+ data

Abstract

Continuous wave EPR and pulsed EPR measurements for Mn2+ in (NH4Mg(SO4)2·6H2O are presented and compared with previously published data for Cu2+. These data are analysed together, to extract an effect from Jahn-Teller dynamics on the electron spin relaxation of the Cu2+ ion. It is possible to estimate the Debye temperature of the crystal as ΘD = 240 K both for Mn2+ and Cu2+, and to prove that the vibronic dynamics do not influence T 1 for Cu2+ up to about 100 K, and only an enhancement of the phase relaxation rate 1/T M by excitations to the higher vibronic level above 20 K is observed. The spin-lattice relaxation rate is higher for Cu2+ than for Mn2+ over the whole temperature range, indicating that the g factor phonon modulation mechanism of Cu2+ relaxation is more effective than the D tensor modulation mechanism of Mn2+ relaxation. From a comparison with other relaxation data for Jahn-Teller systems, it is concluded that an enhancement of the relaxation rate is not as strong as suggested previously and can be different depending on the shape of the adiabatic potential surface.