Nuclear magnetic resonance study of the magnetic line phases in SrCoO _x (2.5 ≤  ×  ≤ 3)

A ⁵⁹Co spin-echo nuclear magnetic resonance (NMR) study, along with complimentary magnetization and x-ray diffraction characterization, is reported for three of the four magnetic line phases which occur in the hole-doped perovskite system SrCoO _x , 2.5 ≤  x  ≤ 3. The magnetic line phases are the single-valence state end-member compounds SrCoO_2.5 and SrCoO₃, as well as the mixed-valence state compound SrCoO_2.88. In this work, the Co valence was varied by changing the oxygen stoichiometry through electrochemical oxidation/reduction. Antiferromagnetic SrCoO_2.5, with trivalent Co³⁺ (3d⁶), is characterized by a single strong, relatively narrow, ⁵⁹Co NMR peak centered at 314 MHz. The 314 MHz peak frequency can be explained using a typical 3d hyperfine coupling constant and the Co moment value ≈3 μ _B obtained from neutron diffraction measurements. Ferromagnetic SrCoO₃ with tetravalent Co⁴⁺ (3d⁵), is characterized by a single strong, relatively narrow, ⁵⁹Co NMR peak centered at 93 MHz. However, the 93 MHz peak frequency is considerably smaller than expected from the 2.1 μ _B Co moment values obtained from the saturation magnetization indicating a significant orbital contribution. Ferromagnetic and mixed-valent (Co³⁺/Co⁴⁺) SrCoO_2.88 is characterized by three broad ⁵⁹Co peaks, centered at 47, 134, and 280 MHz, consistent with previous reports. Based on the NMR results from the end-member compounds, the 280 MHz peak is most likely due to Co³⁺ and not Co⁴⁺ as previously reported. (paper)