Polycrystalline ${\mathrm{Cu}}_{1-x}{\mathrm{Mn}}_x\mathrm{O}$ has been fabricated by the standard solid-state reaction method in the concentration range $0⩽x⩽0.05$. Ferromagnetic characteristics are observed except for the $x⩽0.002$ samples. X-ray diffraction spectra show a pure CuO phase when $x⩽0.0125$ and the appearance of a secondary phase ${\mathrm{Mn}}_2{\mathrm{O}}_3$ when $x⩾0.03$. Analyses of the x-ray photoelectron spectroscopy, the unit cell volume, and magnetism indicate that manganese in the form of ${\mathrm{Mn}}^{2+}$ is incorporated into CuO for the $x⩽0.0125$ samples. The susceptibility of ${\mathrm{Cu}}_{1-x}{\mathrm{Mn}}_x\mathrm{O}$ $(0.004⩽x⩽0.0125)$ can be well fitted by the modified Curie-Weiss law above the Curie temperature. To improve the magnetism, we additionally doped a third element aluminum in ${\mathrm{Cu}}_{1-x}{\mathrm{Mn}}_x\mathrm{O}$ $(x=0.004,0.0075)$ and observed an enhancement of the ferromagnetism. In order to investigate the role of holes in ferromagnetic coupling, lithium was also doped in the sample using the sol-gel method, and a suppression of ferromagnetism was observed (ferromagnetism completely disappears when $y⩾0.03$ in ${\mathrm{Cu}}_{0.9925-y}{\mathrm{Mn}}_{0.0075}{\mathrm{Li}}_y\mathrm{O}$). The observed ferromagnetism in Mn-doped CuO is discussed on the basis of the formation of bound magnetic polarons.

• Received 24 July 2006

DOI:https://doi.org/10.1103/PhysRevB.75.174444