5 research outputs found
Origin of Multiferroism of <i>β</i>-NaFeO<sub>2</sub>
The multiferroic β-NaFeO2 is theoretically investigated for the first time using a microscopic model and Green’s function technique. A small room-temperature ferromagnetism is observed, which could be explained by canting of the antiferromagnetic sublattices. The ferromagnetic behaviour can be applied to applications in spintronic devices. We have investigated the temperature and magnetic field dependence of the spontaneous polarization Ps, as calculated from the transverse Ising model and the spin-assisted polarization ΔP due to magnetostriction and antisymmetric Dzyaloshinsky–Moriya interactions. The influence of external magnetic fields along the y and z axis is discussed. This is indirect evidence for the multiferroic behaviour of NaFeO2. The temperature dependence of the relative dielectric permittivity is calculated
Size and Ion-Doping Effects on Magnetic, Optical, and Phonon Properties of CuAlO<sub>2</sub> Nanoparticles
The magnetic, optical, and phonon properties of ion-doped CuAlO2 nanoparticles on the Cu or Al site are theoretically investigated. The room temperature ferromagnetism in CuAlO2 nanoparticles can be due to the surface, size, and doping effects. The magnetization increases with the decreasing nanoparticle size. The different radii of the transition metal ion and the host Cu ion lead to compressive strain, to the enhancment of the exchange interaction constants, and to increased magnetization Ms and Curie temperature TC. By substitution with Mn or Cr on the Al site, tensile strain, a decrease in Ms, and an increase in dopants are observed. The size and ion-doping influence on the band-gap energy is also discussed. The phonon energy ω decreases, whereas the phonon damping γ increases with increasing temperature and decreasing NP size. They show a kink around TC ∼ 400 K. The behavior of ω and γ for different ion dopings is observed
Origin of Multiferroism in VOX<sub>2</sub> (X = Cl, Br, I) Monolayers
Based on the proposed microscopic model, we investigate the multiferroic characteristics of VOX2 (X = Cl, Br, I) monolayers using a Green’s function method. The dependence of the microscopic parameters of the ferroelectric system (pseudo-spin arrangement and flipping rate) on the magnitude and sign of the exchange magnetic interaction along the b-axis and the value of the Dzyaloshinskii–Moria vector have been investigated and qualitatively explained. The possibility of observing a spin-reorientation transition with a change in the character of spin ordering from antiferromagnetic to ferromagnetic is investigated. It is found that the antisymmetric magnetoelectric interaction may be responsible for the spin-reorientation transition without a change in the ordering of magnetic moments. Changing the sign of the exchange magnetic interaction along the b-axis leads to ferromagnetic ordering without observing a spin-reorientation transition. The dependence of isotropic and antisymmetric magnetic interactions on the microscopic parameters of the ferroelectric system is qualitatively explained. A mechanism for the occurrence of the spin-reorientation transition is presented based on the proposed microscopic model. The obtained results qualitatively coincide with Density Functional Theory calculations
Magnetic, Electric and Optical Properties of Ion Doped CuCr2O4 Nanoparticles
The magnetic, electric and optical properties of pure and ion doped CuCr2O4 - bulk and nanoparticles are investigated theoretically. The magnetization Ms and the band gap Eg decrease with increasing particle size. By Co ion doping Ms and the polarization P show a maximum whereas by Pr ion doping they decrease with increasing the doping concentration. The dielectric constant decreases with enhancing Pr dopants. It is shown that the difference between the doping and host ions radii leads to appearing of a compressive or tensile strain and to different exchange interaction constants in the doped state. Eg decreases by Co doping, whereas it increases by Pr doping
Magnetic, Electric and Optical Properties of Ion Doped CuCr<sub>2</sub>O<sub>4</sub> Nanoparticles
The magnetic, electric and optical properties of pure and ion doped CuCr2O4 - bulk and nanoparticles are investigated theoretically. The magnetization Ms and the band gap Eg decrease with increasing particle size. By Co ion doping Ms and the polarization P show a maximum whereas by Pr ion doping they decrease with increasing the doping concentration. The dielectric constant decreases with enhancing Pr dopants. It is shown that the difference between the doping and host ions radii leads to appearing of a compressive or tensile strain and to different exchange interaction constants in the doped state. Eg decreases by Co doping, whereas it increases by Pr doping