Determination of The Spin Contributed Knight Shift in Na₀.₃₅ Co O₂ · 1.3 H₂ O

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The spin contributed Knight shift ⁵⁹Kₛ of ⁵⁹Co in the triangular lattice superconductor, Na₀.₃₅CoO₂ · 1.3H₂O, has been estimated by NMR experiments in an oriented 2-dimensional powder sample. The Knight shift in the paramagnetic state was estimated by δν/(γₙHᵢ) vs. (γₙHᵢ)⁻² plot at various temperatures. A Knight shift vs. magnetic susceptibility diagram revealed that at least 0.3 % for Kₓ and 0.1 % for Ky are attributed to the spin contribution. Below Tc, δν/(γₙHᵢ) vs. (γₙHᵢ)⁻² plot does not give unique Knight shift because of the diamagnetic effect and/or the other ones. We concluded that the invariant behavior at about 7 T (between Hc₁ and Hc₂) below Tc possibly indicates the nature of the spin-triplet superconductivity.