Exchange interactions in rare earth iron garnets

The exchange magnetic fields at Eu ions inside various rare earth iron garnets were estimated from measurements of the splittings of the 103-keV Mössbauer line of ¹⁵³Eu. Mössbauer sources of the composition (M_0.975 ¹⁵³Sm_0.025) ₃Fe₅O₁₂ were prepared with radioactive Sm ₂O₃ and an absorber of Eu₂O₃ was used. The splittings for diamagnetic Lu and Y were the same although the atomic cell sizes of YIG and LuIG differ by ∼1%. This indicates that the rare-earth iron-exchange interaction in the garnets is not very sensitive to the cell sizes of the garnets. For Gd the splitting was (8.0±1.5)% smaller than for Lu or Y, showing that the exchange field (at the Eu ions) produced by the Gd ions is about 8% of the field produced by the Fe ions. The Eu ³⁺-rare-earth exchange interactions were found to be approximately proportional to 〈S〉 = (g_J-1) 〈J〉.