Exchange-coupled pairs of Yb 3+ ions in SrF 2

摘要: Detailed investigations of the spin-lattice relaxation single ${\mathrm{Yb}}^{3+}$ ions at trigonal sites in ${\mathrm{SrF}}_{2}$ are reported. The measurements were performed 2--12 K temperature range, X band, by using a pulse-sequence saturation method and compared with earlier Q-band measurements. At T\ensuremath{\ge}7.5 is described both frequencies an Orbach process. lower temperatures (2\ensuremath{\le}T\ensuremath{\le}6 K), ${T}_{1}$ exhibits departure from linear dependence, unexpected shorter values, lack anisotropy. This interpreted considering cross fast relaxing pairs exchange-coupled same symmetry Zeeman splittings. governed process which involves transitions between S'=1 ground S'=0 excited states, separated J=-12.5 K. Consequently, low-temperature (2\ensuremath{\le}T\ensuremath{\le}12 K) ${T}_{1}^{\mathrm{\ensuremath{-}}1}$ = 142.2 / exp(12.5/T)-1 +7.731${B}^{5}$coth( h\ensuremath{\nu} 2kT )+0.197\ifmmode\times\else\texttimes\fi{}${10}^{9}$exp(-111.67 T ) . .sp analysis ESR spectra confirms presence such weakly Jl0, representing about 1% total content ions.