The Fe³⁺ and Co²⁺ NMR spectra for Ba_0.3Sr_1.7Co₂ (Fe_0.96Al_0.04)₁₂O₂₂ (BSCFAO) and Ba_0.3Sr_1.7Co₂Fe₁₂O₂₂ (BSCFO) were obtained in a zero magnetic field at a low temperature. We observed change in the enhancement effect of the NMR signals depending on the setting field, which was varied when applied along the b-axis and then turned off before the measurement was taken. The experimental results indicate that the magnetic structure changes from an alternating longitudinal cone to a transverse cone when the setting field is 250 mT. They also show that the spins of Co²⁺ ions together with those of Fe³⁺ ions constitute a part of the overall magnetic structure and that the substitution of Al³⁺ for Fe³⁺ weakens the magnetic anisotropy within the easy plane. From a comparison of the enhancement factors of the Fe³⁺ NMR obtained with the RF pulse applied along the a-axis and the c-axis, we realized that the magnetic easy plane anisotropy is approximately 16 times greater than the anisotropy within the easy plane. No changes of the NMR spectra were observed under an electric field of 1.2 MV/m.

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