<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">Cu</mml:mi></mml:mrow><mml:mprescripts/><mml:mrow/><mml:mrow><mml:mn>63</mml:mn></mml:mrow><mml:mrow/><mml:mrow/></mml:mmultiscripts></mml:mrow></mml:math>NMR shift and linewidth anomalies in the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="italic">T</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="italic">c</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>=60 K phase of Y-Ba-Cu-O

$^{63}\mathrm{Cu}$ NMR shifts and spectra are presented for both Cu(1) and Cu(2) sites in a specimen of ${\mathrm{YBa}}_{\mathit{z}}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.64}$ (${\mathit{T}}_{\mathit{c}}$\ensuremath{\sim}60 K). For H along the c axis, the Cu(2) shift is not distinguishable from that reported for ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7.0}$. For H in the a-b plane, the spin component of Cu(2) shift declines sharply as T\ensuremath{\rightarrow}${\mathit{T}}_{\mathit{c}}$. The Cu(1) shift behaves similarly, showing also a dramatic broadening at low temperatures in clearly nonmetallic behavior. Combined with anomalous ${\mathit{T}}_{1}$ data reported earlier for the 60-K phase of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathit{x}}$, these results are shown to be consistent with strong and monotonically increasing antiferromagnetic correlations as T is decreased.

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