Hyperfine interaction studies of antiferromagnetic order in CuO

The hyperfine field, $H_{\mathrm{hf}}\mathrm{}\left(T\right)\mathrm{}$, in polycrystalline CuO has been studied by ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer-source spectroscopy (MS), ${\mu }_{+}$ spin rotation $\mu \mathrm{S}\mathrm{R}$, and ${}_{}{}^{100}{}_{}{}^{}\mathrm{Rh}$ perturbed angular correlation (PAC) over $4\mathrm{K}<T<\mathrm{}295\mathrm{}\mathrm{K}$. Antiferromagnetic order is observed below $T_N=226\mathrm{}\left(1\right)\mathrm{}$ K. MS and PAC each exhibit a single dominant site with no $K$-capture aftereffects while $\mu \mathrm{S}\mathrm{R}$ has five components. For $\mu \mathrm{S}\mathrm{R}$ and PAC $H_{\mathrm{hf}}\mathrm{}\left(T\right)\mathrm{}$ is well approximated by spin $S=\frac{1}{2}$ mean-field theory; for MS it is anomalous, indicating a significant difference in spin between Fe and Cu and/or moment coupling for Fe-Cu and Cu-Cu. There is no evidence for long-range dynamic correlations, as observed for ${\mathrm{La}}_2$Cu${\mathrm{O}}_4$.