Anisotropic magnetic susceptibility of erbium and ytterbium in zircon, ZrSiO4

Magnetic susceptibility measurements have been made for both Er- and Yb-doped (1̃0³ppm) zircon single crystals with the magnetic field perpendicular and parallel to the [001] axis. Large susceptibility anisotropies were found in both cases. Our observed anisotropies of ZrSiO₄: Yb indicate small populations (1̃9%) of Yb ions at the axial (tetragonal) sites, as the susceptibility of ZrSiO₄: Yb would be nearly isotropic if the Yb ions only occupied the orthorhombic sites. For Er³⁺ in orthorhombic sites of zircon, our data indicate that the first excited state is paramagnetic with g_x = 9 and g_y 5̃ at 20 cm⁻¹ above the ground state (g_x 0̃, g_y 1̃5). The first excited state is quite similar to the ground states observed for Er³⁺ in many host lattices