Since several years, rare-earth nitrides have been focused by experimental and theoretical groups. Especially, gadolinium nitride (GdN) thin films were subject of recent investigations [1]. GdN is ferromagnetic with a Curie temperature lying between 60 and 70 K. The electronic properties of the material are still controversially discussed. While theoretical models vary from semimetallic to semiconducting or even half-metallic, there is still a lack of reliable experimental data. Up to now, the investigated GdN films were polycrystalline with a preferred crystallite orientation. Recently, epitaxial GdN films were presented that were deposited on MgO(100) substrates by ion-beam assisted molecular-beam epitaxy (IBA-MBE) [2].
Aim of this study is to investigate the influence of the substrate temperature on the orientation and the crystalline quality of GdN films prepared on MgO(100) by IBA-MBE. The GdN films were deposited by evaporation of Gd using a high-temperature effusion cell and by simultaneously irradiating the Gd vapor, condensing on the heated MgO substrate (temperature between 150 and 750 °C), by nitrogen ions possessing a maximum kinetic energy of 25 eV. The growth of the GdN films was monitored in situ by reflection high-energy electron diffraction. Highly resolved x-ray diffraction was used to investigate the orientation and the crystalline quality of the films. Furthermore, x-ray texture goniometry was performed to characterize the texture of the films. In order to prove the films to be ferromagnetic, measurements with a superconducting quantum interference device were conducted.
The results show that the orientation of the films changes from {100} epitaxial to {111} preferred oriented for substrate temperatures below 200°C. The crystalline quality of the films, as estimated by x-ray diffraction rocking curves, exhibits a broad minimum between 450 and 600°C. Representative magnetic measurements show a Curie temperature of ~ 70 K. The presented results are discussed with respect to the influence of the preparation parameters on the GdN film properties.
[1] F. Leuenberger, A. Parge, W. Felsch, K. Fauth, M. Hessler, Phys. Rev. B 72 (2005) 014427
[2] J.W. Gerlach, J. Mennig, B. Rauschenbach, Appl. Phys. Lett. 90 (2007) 061919 |