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

Continuous wave EPR and pulsed EPR measurements for Mn2+ in (NH4)(2)Mg(SO4) (2). 6H(2)O are presented and compared with previously published data for C u2+. These data are analysed together, to extract an effect from Jahn-Telle r dynamics on the electron spin relaxation of the Cu ion. It is possible to estimate the Debye temperature of the crystal as Theta(D) = 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 relaxati on rate 1/T-M by excitations to the higher vibronic level above 20 K is obs erved. The spin-lattice relaxation rate is higher for Cu2+ than for Mn2+ ov er the whole temperature range, indicating that the g factor phonon modulat ion mechanism of Cu2+ relaxation is more effective than the D tensor modula tion mechanism of Mn2+ relaxation. From a comparison with other relaxation data for Jahn-Teller systems, it is concluded that an enhancement of the re laxation rate is not as strong as suggested previously and can be different depending on the shape of the adiabatic potential surface.