Magnetic States of Iron Ions in Perovskite Bi_(0.75)Sr_(0.25)Fe_(0.95)Cr_(0.05)O_(3-y)

摘要

~(57)Fe hyperfine interactions are measured in cubic perovskite Bi_(0.75)Sr_(0.25)Fe_(0.95)Cr_(0.05)O_(3-y) by means of M?ssbauer spectroscopy in the temperature range of 95—800 K. The temperature of the magnetic phase transition (Neél point T_N) is measured T_N = 633 (5) K. The experimental spectra at T< T_N show a partially resolved magnetic hyperfine structure with broadened lines described satisfactorily by the superposition of four sextets. Hyperfine magnetic field Hn and isomeric δ and quadrupole ε shift values at room temperature show that all iron ions are in the trivalent state. Three sextets with the same isomer shifts （δ_j ≈δ_2≈0.38 mm/s) correspond to iron ions in an octahedral oxygen environment; the fourth sextet (δ_3 =0.20 mm/s), to iron ions in the square-pyramidal oxygen environment.