Nuclear Magnetic Resonances of Mo⁹⁵, Mo⁹⁷ and Fe⁵⁷ in Ba₂(FeMo)O₆, Sr₂(FeMo)O₆ and Ca₂(FeMo)O₆

Abstract

Nuclear magnetic resonances of Mo⁹⁵, Mo⁹⁷ and Fe⁵⁷ in Ba₂(FeMo)O₆, Sr₂(FeMo)O₆ and Ca₂(FeMo)O₆ with ordered perovskite structure were studied in their ferrimagnetic state by spin echo method. The Mo⁹⁵ and Mo⁹⁷ spin echo signals at 4.2°K were observed between 33.0 MHz to 65.6 MHz, 30.5 MHz to 81.2 MHz and 31.5 MHz to 79.6 MHz, respectively. The Mo⁹⁵ spin echo peak frequencies of these compounds (54.4 MHz, 67.6 MHz and 63.4 MHz, respectively) are higher in the compound with higher ferrimagnetic Néel temperature. In Ba₂(FeMo)O₆, the Mo⁹⁵ spin echo peak shifts to higher frequencies with increasing external static magnetic field. The measured hyperfine fields of the Mo⁵⁺ ions in these compounds are far smaller than the value of the orbital hyperfine field which is expected when the magnitude of the effective orbital angular momentum is 1. The Fe⁵⁷ spin echo signal in Ba₂(FeMo)O₆ at 4.2°K was found at 79 MHz.