Structure and magnetic properties of pure and Gd-doped HfO2 thin films

Pure HfO2 and Gd-doped HfO2 thin films have been grown on different single crystal substrates silicon, R-Al2O3, and LaAlO3 by pulsed laser deposition. X-ray diffraction XRD patterns show that the pure HfO2 thin films are of single monoclinic phase. Gd-doped HfO2 films have the same XRD pattern except that their diffraction peaks have a shift toward lower angles, which indicates that Gd dissolves in HfO2. Transmission electron microscopy images show a columnar growth of the films. Very weak ferromagnetism is observed in pure and Gd-doped HfO2 films on different substrates at 300 and 5 K, which is attributed to either impure target materials or signals from the substrates. The magnetic properties do not change significantly with postdeposition annealing of the HfO2 films. In addition to the films, HfO2 powders were annealed in pure hydrogen flow, and a ferromagnetic signal was not observed.