Spontaneous ferroelectricity in strained low-temperature monoclinic Fe3O4: A first-principles study

Abstract

As a single phase multiferroic material, Fe 3 O 4 exhibits spontaneous ferroelectric polarization below 38 K. However, the nature of ferroelectricity in Fe 3 O 4 and external disturbance like strain on it remain ambiguous. Here, the spontaneous ferroelectric polarization of low-temperature monoclinic Fe 3 O 4 was investigated by first-principles calculations. The pseudo-centrosymmetric FeB42-FeB43 pair has a different valence state. The noncentrosymmetric charge distribution results in the ferroelectric polarization. The initial ferroelectric polarization direction is in the minus direction of x and z axes. The ferroelectricity along y axis is limited due to the symmetry of Cc space group. Both the ionic displacement and charge separation at FeB42-FeB43 pair are affected by strain, which further influences the spontaneous ferroelectric polarization of monoclinic Fe 3 O 4 . The ferroelectric polarization along z axis shows an increase of 45.3% as the strain changes from 6% to -6%.

Atomic-Scale Mechanism of Grain Boundary Effects on the Magnetic and Transport Properties of Fe3O4 Bicrystal Films

“…A 1 × 3 × 1 k -point grid centered at Γ point was set. The on-site Coulomb interaction parameter U = 4.5 eV and on-site exchange interaction parameter J = 0.89 eV were used for Fe ions as in previous works. ,− During the structure optimizations, only the positions of O ions are optimized, while the Fe ions are fixed. The structure optimizations stop after the total energy change becomes less than 10 –5 eV and the Hellman–Feynman force of the optimized structure becomes less than 10 –2 eV/Å.…”

“…Magnetite (Fe 3 O 4 ) is regarded as a candidate in spintronic devices, which attracts much attention due to its magnetic and electronic properties including ferrimagnetism and half-metallicity. − In epitaxial Fe 3 O 4 films, the stacking fault generates widely distributed antiphase boundaries (APBs), where Fe A -O-Fe A and Fe B –O–Fe B are antiferromagnetic coupled. − Such abnormal magnetic interaction enlarging the magnitude of MR in Fe 3 O 4 films suggests the sensitivity of physical properties in Fe 3 O 4 to the local lattice structure. ,− What is more, as the temperature decreases to about 120 K ( T V ), Fe 3 O 4 undergoes Verwey transition. − The metastable lattice structure and magnetic properties of Fe 3 O 4 in the vicinity of T V are susceptible to lattice strain, stoichiometry, and thickness. ,, When considering the introduction of GB, the producing effects of the unique lattice structure at GBs on the electronic structure, transport, magnetic properties and Verwey transition in Fe 3 O 4 bicrystal films are not reported yet.…”

Negative differential resistance and magnetotransport in Fe3O4/SiO2/Si heterostructures

“…The electric field inhomogeneity in the space charge region generates a positive MR. 39,40 With the decrease in temperature, the increased carriers' mobility aggravates the spatial distribution of the space charge region, which results in a decrease in MR. Figure 4(c 41,42 and so MR may come from the spin accumulation in the space charge region of p-Si. 43,44 Due to the nonmagnetic essence of p-Si, the accumulated spin-polarized carriers align to the applied magnetic field.…”