Magnetic Properties of $La_3Ga_{5.5}Ta_{0.5}O_{14}$ Single Crystals Doped with Sm³⁺ and Er³⁺ Ions

Electron paramagnetic resonance and magnetic susceptibility measurements were performed for two $La_3Ga_{5.5}Ta_{0.5}O_{14}$ single crystals doped with 1.96 at.% of Sm³⁺ ions and 3.8 at.% of Er³⁺ ions. Two magnetically inequivalent sites were found to be responsible for the electron paramagnetic resonance spectra of Sm³⁺ ions. Both sites reveal a low (at least C₂) symmetry with $g_{x}$~0.46, $g_{y}$~0.46 and $g_{z}$~0.52. The symmetry of isolated erbium ions is higher than C₂. From electron paramagnetic resonance and magnetic susceptibility experiments it results that the ground state of Er³⁺ ions is Γ⁶ or Γ⁷. Below 51 K electronic transitions within Γ⁶ doublets take place. Between 51 and 60 K, Γ⁶ to Γ⁷ transitions dominate, while above 60 K mainly transitions within Γ⁷ doublet are active.