Ca3−xSrxCo4O9 with different compositions (x=0, 0.15, 0.3, and 0.45) were synthesized from stoichiometric mixtures of Co3O4, CaCO3, and SrCO3, and their unit-cell parameters were determined. The powders were mixed with silicon standard powder, and XRD patterns were collected and analyzed using TOPAS. The compounds were determined to be monoclinic with space group of P2. Unit-cell parameters changed from a=4.8329(3) Å, b=4.5727(1) Å, c=10.8360(4) Å, and β=98.093(7)° when x=0, to a=4.8432(1) Å, b=4.6100(3) Å, c=10.8668(3) Å, and β=98.110(5)° when x=0.3. An unidentified second phase was observed when x=0.45.

Ferromagnetic Cu-doped GaN film was grown on a GaN-buffered sapphire (0001) substrate by a hybrid physical-chemical-vapor-deposition method (HPCVD). The GaCuN film (Cu: 3.6 at.%) has a highly c-axis-oriented hexagonal wurtzite crystal structure, which is similar to GaN buffer but without any secondary phases such as metallic Cu, CuxNy, and CuxGay compounds. Two weak near-band edge (NBE) emissions at 3.38 eV and donor-acceptor-pair (DAP) transition at 3.2 eV with a typical strong broad yellow emission were observed in photoluminescence spectra for GaN buffer. In contrast, the yellow emission was completely quenched in GaCuN film because Ga vacancies causing the observed yellow emission in undoped GaN were substituted by Cu atoms. In addition, GaCuN film exhibits a blue shift of NBE emission, which could be explained with the +2 oxidation state of Cu ions, replacing +3 Ga ions resulting in band gap increment. The valance sate of Cu in GaCuN film was also confirmed by x-ray photoelectron spectroscopy (XPS) analysis. The GaCuN film shows ferromagnetic ordering and possesses a residual magnetization of 0.12 emu/cm3 and a coercive field of 264 Oe at room temperature. The unpaired spins in Cu2+ ions (d9) are most likely to be responsible for the observed ferromagnetism in GaCuN.

TbMnO3 exists in an orthorhombic phase in nature. Recently, we successfully grew TbMnO3 thin films in the hexagonal phase using epitaxial stabilization techniques. In this article, we will show the details of the deposition conditions that allow us to fabricate the hexagonal TbMnO3 films on Pt–Al2O3(0001) substrates. The artificial hexagonal phase can be easily formed above 850 °C, irrespective of the oxygen partial pressure. The hexagonal TbMnO3 films showed ferroelectric properties, which are significantly enhanced compared to those of the orthorhombic TbMnO3 bulk phase. We find interesting anomalies in the magnetic and magnetodielectric properties of the TbMnO3 films at around 45 K, which should be related with the Mn3+ spin reorientation. We also find spin-glass-like behaviors in the magnetic susceptibility, which could be attributed to the geometric frustration of antiferromagnetically coupled Mn spins with an edge-sharing triangular lattice. This work shows details of the growth and properties of hexagonal TbMnO3 films.