Spin Structure Change in Co-Substituted BiFeO₃

Development of Bismuth Ferrite as a Piezoelectric and Multiferroic Material by Cobalt Substitution

“…The spectrum at 300 K was well fitted by one component with a Zeeman sextet with a symmetric height and an IS of 0.385 mm s −1 , QS of −0.216 mm s −1 , and B hf of 47.6 T. The symmetric spectrum is indicative of the collinear spin structure . The values of IS, QS, and B hf were comparable with those of the bulk sample, as mentioned in Section . The area intensity ratio of the six lines was close to 3:4:1:1:4:3.…”

“…The change in the ratio of the collinear phase nearly agreed with the change in M r . This result clearly demonstrates the coexistence of the collinear phase and cycloidal phase below 300 K. The reason the spectra evidently looked symmetric even at 150 K was probably because the volume fraction of the cycloidal phase in the x = 0.10 thin film was expected to be only ≈0.5, and the degree of asymmetry in the cycloidal phase was basically small as seen for bulk BiFe 0.9 Co 0.1 O 3 . It should also be noted that anharmonicity in the cycloidal modulation, which is taken into account to describe the Mössbauer spectra of BiFeO 3 thin films and nanoparticles, was not considered explicitly in this analysis.…”

“…We discovered a temperature‐induced spin structure change from a cycloidal to a collinear one in bulk BiFe 0.8 Co 0.2 O 3 , as mentioned in the introduction of Section . To clarify the nature of this spin structure change, the composition dependence of the magnetic properties was studied in detail . The temperature dependence of the magnetic susceptibility of BiFe 1− x Co x O 3 ( x = 0.05, 0.10, 0.15, and 0.20) is shown in Figure a.…”

“…e) Temperature dependence of the fraction of the collinear phase estimated from the Mössbauer spectra and that of the magnetic susceptibility. Adapted with permission . Copyright 2016, The Physical Society of Japan.…”

“…The present result also suggests the appearance of the cycloidal phase in the thin‐film sample at lower temperatures, as was indicated by the temperature dependence of magnetization. To analyze the spin structure of the low‐temperature phase, we used a similar approximate model with two representative components (positive and negative QSs with a 2:1 ratio in absolute value) as was applied for the analysis of the bulk BiFe 0.9 Co 0.1 O 3 . The only difference was that we added the constraint that the intensity ratio of the first component with negative QS was 3:4:1:1:4:3, which represents the in‐plane spin component of the cycloidal phase and the collinear phase.…”