Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userInelastic neutron scattering studies of YFeO$_3$
132
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Spin waves in the the rare earth orthorferrite YFeO$_3$ have been studied by inelastic neutron scattering and analyzed with a full four-sublattice model including contributions from both the weak ferromagnetic and hidden antiferromagnetic orders. Antiferromagnetic (AFM) exchange interactions of $J_1 = -4.23 pm 0.08$ (nearest-neighbors only) or $J_1 = -4.77 pm 0.08$ meV and $J_2 = -0.21 pm 0.04$ meV lead to excellent fits for most branches at both low and high energies. An additional branch associated with the hidden antiferromagnetic order was observed. This work paves the way for studies of other materials in this class containing spin reorientation transitions and magnetic rare earth ions.
rate research
Read More
By the single crystal inelastic neutron scattering the orthoferrite HoFeO3 was studied. We show that the spin dynamics of the Fe subsystem does not change through the spin-reorientation transitions. The observed spectrum of magnetic excitations was analyzed in the frames of linear spin-wave theory. Within this approach the antiferromagnetic exchange interactions of nearest neighbors and next nearest neighbors were obtained for Fe subsystem. Parameters of Dzyaloshinskii-Moriya interactions at Fe subsystem were refined. The temperature dependence of the gap in Fe spin-wave spectrum indicates the temperature evolution of the anisotropy parameters. The estimations for the values of Fe-Ho and Ho-Ho exchange interaction were made as well.
The structure and dynamical properties of the Fe$_3$Si/GaAs(001) interface are investigated by density functional theory and nuclear inelastic scattering measurements. The stability of four different atomic configurations of the Fe$_3$Si/GaAs multilayers is analyzed by calculating the formation energies and phonon dispersion curves. The differences in charge density, magnetization, and electronic density of states between the configurations are examined. Our calculations unveil that magnetic moments of the Fe atoms tend to align in a plane parallel to the interface, along the [110] direction of the Fe$_3$Si crystallographic unit cell. In some configurations, the spin polarization of interface layers is larger than that of bulk Fe$_3$Si. The effect of the interface on element-specific and layer-resolved phonon density of states is discussed. The Fe-partial phonon density of states measured for the Fe$_3$Si layer thickness of three monolayers is compared with theoretical results obtained for each interface atomic configuration. The best agreement is found for one of the configurations with a mixed Fe-Si interface layer, which reproduces the anomalous enhancement of the phonon density of states below 10 meV
Sodium niobate (NaNbO3) exhibits most complex sequence of structural phase transitions in perovskite family and therefore provides as excellent model system for understanding the mechanism of structural phase transitions. We report temperature dependence of inelastic neutron scattering measurements of phonon densities of states in sodium niobate. The measurements are carried out in various crystallographic phases of this material at various temperatures from 300 K to 1048 K. The phonon spectra exhibit peaks centered around 19, 37, 51, 70 and 105 meV. Interestingly, the peak around 70 meV shifts significantly towards lower energy with increasing temperature, while the other peaks do not exhibit an appreciable change. The phonon spectra at 783 K show prominent change and become more diffusive as compared to those at 303 K. In order to better analyze these features, we have performed first principles lattice dynamics calculations based on the density functional theory. The computed phonon density of states is found to be in good agreement with the experimental data. Based on our calculation we are able to assign the characteristic Raman modes in the antiferroelectric phase to the A1g symmetry, which are due to the folding of the T (w=95 cm-1) and delta(w=129 cm-1) points of the cubic Brillouin zone.
Lattice dynamics and high pressure phase transitions in AWO4 (A = Ba, Sr, Ca and Pb) have been investigated using inelastic neutron scattering experiments, ab-initio density functional theory calculations and extensive molecular dynamics simulations. The vibrational modes that are internal to WO4 tetrahedra occur at the highest energies consistent with the relative stability of WO4 tetrahedra. The neutron data and the ab-initio calculations are found to be in excellent agreement. The neutron and structural data are used to develop and validate an interatomic potential model. The model is used for classical molecular dynamics simulations to study their response to high pressure. We have calculated the enthalpies of the scheelite and fergusonite phases as a function of pressure, which confirms that the scheelite to fergusonite transition is second order in nature. With increase in pressure, there is a gradual change in the AO8 polyhedra, while there is no apparent change in the WO4 tetrahedra. We found that that all the four tungstates amorphize at high pressure. This is in good agreement with available experimental observations which show amorphization at around 45 GPa in BaWO4 and 40 GPa in CaWO4. On amorphization, there is an abrupt increase in the coordination of the W atom while the bisdisphenoids around A atom are considerably distorted. The pair correlation functions of the various atom pairs corroborate these observations. Our observations aid in predicting the pressure of amorphization in SrWO4 and PbWO4, which have not been experimentally reported.
YFeO$_3$ thin films are a recent addition to the family of multiferroic orthoferrites where Ytextsubscript{Fe} antisite defects and strain have been shown to introduce polar displacements while retaining magnetic properties. Complete control of the multiferroic properties, however, necessitates knowledge of the defects present and their potential role in modifying behavior. Here, we report the structure and chemistry of antiphase boundaries in multiferroic YFeO$_3$ thin films using aberration corrected scanning transmission electron microscopy combined with atomic resolution energy dispersive X-ray spectroscopy. We find that Fetextsubscript{Y} antisites, which are not stable in the film bulk, periodically arrange along antiphase boundaries due to changes in the local environment. Using density functional theory, we show that the antiphase boundaries are polar and bi-stable, where the presence of Fetextsubscript{Y} antisites significantly decreases the switching barrier. These results highlight how planar defects, such as antiphase boundaries, can stabilize point defects that would otherwise not be expected to form within the structure.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
