Susceptibility measurements have been carried out on single-crystal LaCoO3 in the temperature range of 4.2° to 300°K. We find an effective magnetic moment squared that agrees with Heikes et al. at 300°K, but which falls more rapidly with decreasing temperature. Paramagnetic resonance measurements at 4.2°, 77°, and 300°K have ruled out the presence of modest quantities of paramagnetic cobalt, leaving only the possibilities of diamagnetic or highly concentrated paramagnetic Co+3. (Large concentrations of other cobalt valencies are ruled out for chemical reasons.) Using a model found successful by Goodenough, we assume that Co+3 is near the crossover point, with the 1A1 state lowest. A calculation including spin-orbit effects, but assuming cubic symmetry for the 300° to 4.2°K range, gives essentially a linear variation for the energy difference between the 1A1 and the center of gravity of the 5T2 states, opposite to that expected for a cubic variation. This effect can be explained by including a lower symmetry distortion (probably trigonal) which increases with decreasing temperature, similar to that found in LaAlO3:Cr.

No abstract

No abstract

The widths and positions of the R and N lines in heavily doped ruby have been measured at temperatures from 13° up to 450°K. The results for the temperature dependence of the linewidths are explained in terms of microscopic strains, Raman scattering of phonons by the impurity ions, and direct phonon processes. The results for the lineshifts with temperature are due to the absorption and emission of virtual phonons. A Debye model of phonons is used with different effective phonon distributions for the linewidth and lineshift processes. Also the effective phonon distribution for the broadening of pair (N) lines is different from that for the broadening of single ion (R) lines.

No abstract