Optical Transparency of Rare-Earth Iron Garnets

Abstract

Optical absorption and electrical resistivity have been measured for single‐crystal flux grown rare‐earth iron garnets doped with Si⁴⁺, Sn⁴⁺, Ge⁴⁺, and Ca²⁺. Strong optical absorption near 9000 cm⁻¹ is observed due to relaxation mechanisms involving transfer of an electron from Fe²⁺ ions in the case of Si, Ge, Sn doping, or a hole from Fe⁴⁺ ions in the case of Ca doping to Fe³⁺ ions in the vicinity. This is accompanied by n‐type electrical conductivity for crystals containing Fe²⁺ introduced by Si, Sn, Ge, and by p‐type conductivity for those containing Fe⁴⁺ produced by Ca doping. We find that pure rare‐earth iron garnets contain small amounts (0.004 atom/formula) of Fe⁴⁺ producing undesirable optical absorption, and this can be eliminated by small additions of tetravalent Si, Sn, or Ge.