Nuclear magnetic resonance study of the magnetic line phases in SrCoOx (2.5 ≤ x ≤ 3)

A Co-59 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 SrCoOx, 2.5 <= x <= 3. The magnetic line phases are the single-valence state end-member compounds SrCoO2.5 and SrCoO3, as well as the mixed-valence state compound SrCoO2.88. In this work, the Co valence was varied by changing the oxygen stoichiometry through electrochemical oxidation/reduction. Antiferromagnetic SrCoO2.5, with trivalent Co3+ (3d(6)), is characterized by a single strong, relatively narrow, Co-59 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 approximate to 3 mu(B) obtained from neutron diffraction measurements. Ferromagnetic SrCoO3 with tetravalent Co4+ (3d(5)), is characterized by a single strong, relatively narrow, Co-59 NMR peak centered at 93 MHz. However, the 93 MHz peak frequency is considerably smaller than expected from the 2.1 mu(B) Co moment values obtained from the saturation magnetization indicating a significant orbital contribution. Ferromagnetic and mixed-valent (Co3+/Co4+) SrCoO2.88 is characterized by three broad Co-59 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.