Semiconducting ground state of $\mathrm{GdN}$ thin films

We report the growth of $\mathrm{GdN}$ thin films and a study of their structure and magnetic and conducting properties. It is demonstrated that they are semiconducting at ambient temperature with nitrogen vacancies the dominant dopant. The films are ferromagnetic below $68\mathrm{K}$, and a significant narrowing of the band gap is signaled by more than a doubling of its conductivity. The conductivity in the low-temperature ferromagnetic state remains typical of a doped semiconductor, supporting the view that this material is semiconducting in its ground state and that no metal-insulator transition occurs at the Curie temperature.

Figure 1

XRD of $\mathrm{GdN}$ capped with ${\mathrm{MgF}}_2$ taken at grazing incidence. Unlabeled peaks derive from the ${\mathrm{MgF}}_2$ capping layer.

Figure 2

Magnetic response of a $200\mathrm{nm}$ thick $\mathrm{GdN}$ film capped with $\mathrm{GaN}$. The main window shows the magnetic moment per Gd ion in a field of $0.05\mathrm{T}$ and the inset is a trace of the magnetization vs applied field at a temperature of $5\mathrm{K}$. The coercive field of around $220\mathrm{Oe}$ is too small for the hysteresis to be visible on this scale.

Figure 3

The conductance of $\mathrm{GdN}$ as a function of the pressure of ${\mathrm{N}}_2$ during deposition, recorded during a growth under a continuously diminishing pressure.

Figure 4

Temperature-dependent resistivity of a $200\mathrm{nm}$ thick $\mathrm{GdN}$ film. The pronounced peak at $68\mathrm{K}$ corresponds to the measured Curie temperature of the film. The inset shows the low-temperature behavior of the resistivity.

Figure 5

Optical reflection and transmission for $\mathrm{GdN}$ capped with $\mathrm{GaN}$. The strong absorption onset between 1.5 and $2\mathrm{eV}$ supports the semiconducting model for the film’s room-temperature conductivity.