Magnetic linear birefringence in rare-earth garnets: Crystal-field effects and the Judd-Ofelt approximation

Results of an experimental and theoretical study of the magnetic linear birefringence (MLB) in heavy-rare-earth (RE) garnets ${\mathit{R}}_{3}$${\mathit{M}}_{5}$${\mathrm{O}}_{12}$ (R=Tb,Dy,Ho,Er,Tm,Yb; M=Al,Ga) in magnetic fields up to 5 T and temperature range from 4.2 to 50 K are presented. We demonstrate that the measurements of MLB in RE compounds provide a sensitive method to investigate the adequacy of the Judd-Ofelt approximation. The second-order perturbation theory involving this approximation was found to describe the MLB data for terbium, dysprosium, erbium, and thulium aluminum and gallium garnets within the experimental accuracy. To account for the sign and anisotropy of MLB in ytterbium aluminum and gallium garnets an extension of the theory beyond the Judd-Ofelt approximation is needed. For the case of holmium aluminum and gallium garnets the analysis of the MLB data was hampered by the proximity of an absorption band.

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