Structural and magnetic properties of Cr2O3\mathrm{Cr_{2}O_{3}} at high pressure

The structural and magnetic properties of Cr$_{2}$O$_{3}$ have been studied by means of X-ray and neutron powder diffraction at high pressures up to 35 GPa. The lattice compression of the rhombohedral crystal structure of R $\bar{3}$c symmetry is slightly anisotropic with anomaly in the pressure behavior of the c/a parameters ratio at P $\approx$ 20 GPa of presumably magnetic nature. The oxygen octahedra around chromium ions become more symmetric with close values of shared and unshared bonds under high pressure. The antiferromagnetic structure of Cr$_{2}$O$_{3}$ remains stable in the studied pressure range up to 35 GPa. The pressure coefficient of the Neel temperature, (1/T$_N$)(dT$_N$/dP) = + 0.0091 GPa$^1$, is significantly less in comparison with perovskite-like compounds containing Cr$^{3+}$ and Mn$^{4+}$ ions of similar electronic configuration

Anomalous lattice compression and magnetic ordering in CuO at high pressures: A structural study and first-principles calculations

The structural and magnetic properties of multiferroic CuO have been studied by means of neutron and x-raypowder diffraction at pressures up to 11 and 38 GPa, respectively, and by first-principles theoretical calculations.Anomalous lattice compression is observed, with enlargement of the lattice parameter a, reaching a maximum at P = 13 GPa, followed by its reduction at higher pressures. The lattice distortion of the monoclinic structure at highpressures is accompanied by a progressive change of the oxygen coordination around Cu atoms from the squarefourfold towards the octahedral sixfold coordination. The pressure-induced evolution of the structural propertiesand electronic structure of CuO was successfully elucidated in the framework of full-electronic density functionaltheory calculations with range-separated HSE06, and meta–generalized gradient approximation hybrid M06functionals. The antiferromagnetic (AFM) ground state with a propagation vector q = (0.5,0, − 0.5) remainsstable in the studied pressure range. From the obtained structural parameters, the pressure dependencies of theprincipal superexchange magnetic interactions were analyzed, and the pressure behavior of the N´eel temperatureas well as the magnetic transition temperature from the intermediate incommensurate AFM multiferroic stateto the commensurate AFM ground state were evaluated. The estimated upper limit of the N´eel temperature atP = 38 GPa is about 260 K, not supporting the previously predicted existence of the multiferroic phase at roomtemperature and high pressure

Pressure-Induced Modifications of the Magnetic Order in the Spin-Chain Compound Ca\u3csub\u3e3\u3c/sub\u3eCo\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e6\u3c/sub\u3e

The structural and magnetic properties of the Ca3Co2O6 spin-chain compound have been studied by means of neutron and x-ray powder diffraction at pressures up to 6.8 and 32 GPa, respectively. A suppression of the initial spin-density wave state (TN = 25 K) and stabilization of the collinear commensurate antiferromagnetic (AFM) state at high pressures (TNC = 26 K at P = 2.1 GPa) were observed. The pressure behavior of the competing intra- and interchain magnetic interactions was analyzed on the basis of obtained structural data and their role in the formation of the magnetic phase diagram is discussed. The pressure behavior of the Néel temperature of the commensurate AFM phase was evaluated within the mean field theory approach and a good agreement with the experimental value dTNC/dP = 0.65 K/GPa was obtained

Structural, magnetic and vibrational properties of multiferroic GaFeO3GaFeO_{3} at high pressure

The crystal, magnetic structure and vibrational spectra of multiferroic GaFeO$_3$ have been studied by means of neutron, X-ray powder diffraction and Raman spectroscopy at pressures up to 6.2 and 42 GPa, respectively. A presence of Fe/Ga antisite disorder leads to a formation of the ferrimagnetic ground state with the Néel temperature T$_N$ = 292 K at ambient pressure. Upon compression, the magnetic ground state symmetry remains the same and the Néel temperature increases with a pressure coefficient (1/T$_N$)(dT$_N$/dP) = 0.011(1) GPa$^{−1}$. Application of high pressure above 21 GPa leads to a gradual structural phase transition from the polar orthorhombic Pc2$_1$n phase to nonpolar orthorhombic Pbnm phase. It is accompanied by anomalies in the pressure behaviour of several Raman modes. Pressure dependencies of lattice parameters and Raman modes frequencies in the observed structural phases were obtained

Effect of Plasma Oxygen Content on the Size and Content of Silicon Nanoclusters in Amorphous SiOx Films Obtained with Plasma-Enhanced Chemical Vapor Deposition

The influence of Ar + SiH4 + O2 plasma formulation on the phase composition and optical properties of amorphous SiOx films with silicon nanoclusters obtained using PECVD with DC discharge modulation was studied. Using a unique technique of ultrasoft X-ray emission spectroscopy, it was found that at a 0.15 mol.% plasma oxygen content, amorphous silicon a-Si films are formed. At a high oxygen content (≥21.5 mol.%), nanocomposite films based on SiOx silicon suboxide containing silicon nanoclusters ncl-Si are formed. It was found that the suboxide matrix consists of a mixture of SiO1.3 and SiO2 phases, and the average oxidation state x in the SiOx suboxide matrix is ~1.5. An increase in the concentration of O2 in the reactor atmosphere from 21.5 to 23 mol.% leads to a decrease in ncl-Si content from 40 to 15% and an increase in the average oxidation state x of SiOx from 1.5 to 1.9. In this case, the suboxide matrix consists of two phases of silicon dioxide SiO2 and non-stoichiometric silicon oxide SiO1.7. Thus, according to the experimental data obtained using USXES, the phase composition of these films in pure form differs in their representation in both random coupling and random mixture models. A decrease in the ncl-Si content of SiOx films is accompanied by a decrease in their sizes from ~3 to ~2 nm and a shift in the photoluminescence band from 1.9 eV to 2.3 eV, respectively