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The rare-earth nitrides are ferromagnetic semiconductors with promise for spintronic devices. Their most common dopants are nitrogen vacancies (VN), with a small enough energy of formation that they exist at of order 1% in epitaxial films. Here we report preliminary investigations of their effect on the magnetic states of two of them in the series, GdN and EuN. In the former we find an enhanced Curie temperature at very high VN concentration, and the Eu 2 þ ions associated with V N in the latter show strong exchange with their Eu 3 þ neighbours that might form the basis of a diluted magnetic semiconductor.

We report measurements of the optical response of polycrystalline DyN thin films. The frequency-dependent complex refractive index in the near IR-visible-near UV was determined by fitting reflection/transmission spectra. In conjunction with resistivity measurements, these identify DyN as a semiconductor with an optical energy gap of 1.2 eV. When doped with nitrogen vacancies it shows free carrier absorption and a blue-shifted gap associated with the Moss-Burstein effect. The refractive index of 2.0 ± 0.1 depends only weakly on energy. Far infrared reflectivity data show a polar phonon of frequency 280 cm−1 and a dielectric strength of Δe=20.

We report ${M}_{4,5}$- and ${L}_{2,3}$-edge x-ray magnetic circular dichroism (XMCD) studies of the ion-specific magnetic polarization on Eu in europium mononitride. The absorption spectra at both edges show a main signal originating from Eu${}^{3+}$ with a well-separated small ($~2%$) contribution from a Eu${}^{2+}$ valence state that we propose is associated with a small concentration of N vacancies. Magnetic polarization is observed in both $4f$ and $5d$ orbitals and for both valence states. The temperature and field dependence of the ${M}_{4,5}$-edge XMCD signal shows a van Vleck signature from Eu${}^{3+}$ (main EuN contribution) and a Brillouin paramagnetic signal from the small concentration of Eu${}^{2+}$ ions. In addition, the ${L}_{2,3}$ edge shows that the Eu${}^{3+}$ ions have $5d$ orbitals that are polarized both by intra-ion $f\ensuremath{-}d$ exchange and by inter-ionic $d$-$d$ exchange from neighboring Eu${}^{2+}$ ions. There is no evidence of magnetic order among the Eu ions at temperatures as low as 10 K.