Low temperature magnetic properties of some rare earth trifluoromethanesulfonates

The rare earth trifluoromethanesulfonates, R(CF{dollar}rmsb7SOsb3)sb3.9Hsb2O{dollar} (RTFMS), have a hexagonal structure similar to the familiar rare earth ethylsulfates, R(C{dollar}rmsb2Hsb5SOsb4)sb3.9Hsb2O{dollar} (RES). The magnetic properties of RTFMS and RES analogs for many different rare earths were found to be quite similar. However, the correspondence in the behavior of these compounds appears to break down in the cases of Ce{dollar}rmsp{lcub}3+{rcub}, Prsp{lcub}3+{rcub},{dollar} and Yb{dollar}rmsp{lcub}3+{rcub}{dollar}.; Electron paramagnetic resonance (EPR) spectra of single crystals of the rare earth ions {dollar}rm Cesp{lcub}3+{rcub}, Prsp{lcub}3+{rcub}, and Ybsp{lcub}3+{rcub}{dollar} in the TFMS lattice were studied in the temperature range 1.2 K {dollar}le{dollar} T {dollar}le{dollar} 4.2 K and at frequencies of {dollar}sim{dollar}9 GHz and {dollar}sim{dollar}23 GHz. Resonances from the ground and first excited doublet of Ce{dollar}sp{lcub}3+{rcub}{dollar}, the accidentally degenerate ground doublet of Pr{dollar}sp{lcub}3+{rcub}{dollar}, and the first and second excited doublets of Yb{dollar}sp{lcub}3+{rcub}{dollar} were observed. The single ion spectra of these compounds enabled us to establish the parallel and perpendicular components of the splitting factors of the various doublets that produced a signal, as well as the hyperfine constant for Pr{dollar}sp{lcub}3+{rcub}{dollar}.; EPR techniques were also used to study the nature of interionic interactions in CeTFMS and PrTFMS. An examination of the pair spectra of Ce{dollar}sp{lcub}3+{rcub}{dollar} in LaTFMS revealed that virtual phonon exchange (VPE), while not as strong as in CeES, is the dominant non-dipolar interaction. The antiferromagnetic contribution to non-dipolar interactions in CeTFMS was found to be too weak to overcome the ferromagnetic contribution of dipolar interactions as it does in CeES. In PrTFMS a magnetic moment exists along the crystalline axis of symmetry with a larger electric dipole moment in the perpendicular plane. Short-range order of the one dimensional XY type and long-range order features were observed in the heat capacity. No indication of long-range ordering was observed in PrES. EPR of the pair spectra of Pr{dollar}sp{lcub}3+{rcub}{dollar} in LaTFMS indicates that the interchain interactions are quite sizable allowing the establishment of long-range order. Virtual phonon exchange seems to be the dominant coupling mechanism.; EPR and magnetic susceptibility measurements of YbTFMS indicate that there are deviations from the expected C{dollar}rmsb{lcub}3h{rcub}{dollar} symmetry, exhibited by YbES, that shift the first and second excited doublets closer to the ground doublet. The symmetry lowering strains also appear to depend on the concentration of the Yb{dollar}sp{lcub}3+{rcub}{dollar} ion. An analysis of the data assuming distortions that introduce terms of C{dollar}rmsb{lcub}3v{rcub}{dollar} symmetry was adequate to explain our experimental results.