Thin films of ${\mathrm{HfO}}_2$ produced by pulsed-laser deposition on sapphire, yttria-stabilized zirconia, or silicon substrates show ferromagnetic magnetization curves with little hysteresis and extrapolated Curie temperatures far in excess of $400\mathrm{K}$. The moment does not scale with film thickness, but in terms of substrate area it is typically in the range $150–400{\mu }_{\mathrm{B}}{\mathrm{nm}}^{-2}$. The magnetization exhibits a remarkable anisotropy, which depends on texture and substrate orientation. Pure ${\mathrm{HfO}}_2$ powder develops a weak magnetic moment on heating in vacuum, which is eliminated on annealing in oxygen. Lattice defects are the likely source of the magnetism.

Thin films of $\mathrm{Sn}{\mathrm{O}}_2$ prepared by pulsed-laser deposition on R-cut sapphire substrates exhibit ferromagnetic properties at room temperature when they are doped with Cr, Mn, Fe, Co, or Ni, but not with other $3d$ cations. Extrapolated Curie temperatures are generally in excess of $500\mathrm{K}$. The moment of the films is roughly independent of doping level, from $0.1–15\mathrm{at.}\%$, with a value per unit substrate area of $200\pm 100{\mu }_{\mathrm{B}}{\mathrm{nm}}^{-2}$. When magnetization is expressed as a moment per $3d$ dopant ion, it varies from more than the spin-only value at low concentrations to less than $0.2{\mu }_{\mathrm{B}}$/ion near the percolation threshold. Greatest values are found for iron. The magnetization of the films is highly anisotropic with values when the field is applied perpendicular to the substrate more than double the in-plane values. There is little hysteresis except at high doping levels. The oxides are degenerate $n$-type semiconductors with a Hall mobility of $100{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ and $1.4\times {10}^{19}$ carriers ${\mathrm{cm}}^{-3}$ in a one-band model, but no anomalous Hall effect or magnetoresistance was observed at room temperature. The data are discussed in relation to (a) the donor impurity-band model of ferromagnetism in semiconductors and (b) the magnetic defect model.

The electronic properties of cobalt-doped $\mathrm{ZnO}$ were investigated through site-selective and element-sensitive x-ray-absorption spectroscopy in the vicinity of the Co $L_{2,3}$ edge, the oxygen $K$ edge, and at the Zn $L_3$ edge. The spectroscopic measurements of the ferromagnetic cobalt-doped $\mathrm{ZnO}$ films appear to have additional components in the O $K$ edge x-ray-absorption spectrum not observed in the undoped films. The observed features may derive from both hybridization with unoccupied Co $3d$ states and also from lattice defects such as oxygen vacancies. Only minor changes in the Zn $L_3$ edge spectra were observed. These observations are consistent with a polaron percolation model in which the ferromagnetic coupling is mediated by shallow donor electrons trapped in oxygen vacancies and couples the Co atoms substituted on Zn sites in the hexagonal wurtzite $\mathrm{ZnO}$ structure.

Thin films of 5% Co-doped ZnO with a range of Al codoping exhibit a band-edge shift, which varies with carrier concentration as $n^{2∕3}$ . Carrier effective mass is $0.26m_e$ and mobility is $\sim 10{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ . The doped films, which contain coherent Co clusters of $4–8\mathrm{nm}$ in size, exhibit a ferromagnetic moment of $0.3–1.0{\mu }_B$ per cobalt. The magnetism is progressively destroyed by Al doping due to a reduction in Co-cluster formation. Magnetoresistance appears below $30\mathrm{K}$ , but these materials cannot be regarded as dilute magnetic semiconductors.