G-shift measurements for Yb3+in Tm3Al5O12

Abstract

g shifts arising from interactions with singlet groundstate host lattice Tm3+ ions have been measured by EPR for Yb3+ at orthorhombic sites in cubic Tm3Al5O12. The g values in absence of any Yb-Tm interactions (gCF) have been deduced by two methods. The first involves measurement of the Yb hyperfine parameters (both by EPR and by Mossbauer techniques) which are related to the gCF using the fact that J remains a good quantum number. The second method involves measurement of the g values as a function of host lattice susceptibility chi , the extrapolation to zero chi giving the gCF. Complete agreement between the two sets of gCF values was not obtained. The results show that in fact extrapolation of the g values as a function of the bulk isotropic susceptibility can lead to erroneous results when the local symmetry is lower than cubic. Obtaining the g shifts from the hyperfine values could be a generally useful method in low symmetry systems.