Magnetic ordering induced giant optical property change in tetragonal BiFeO3

Abstract

Magnetic ordering could have significant influence on band structures, spin-dependent transport, and other important properties of materials. Its measurement, especially for the case of antiferromagnetic (AFM) ordering, however, is generally difficult to be achieved. Here we demonstrate the feasibility of magnetic ordering detection using a noncontact and nondestructive optical method. Taking the tetragonal BiFeO3 (BFO) as an example and combining density functional theory calculations with tight-binding models, we find that when BFO changes from C1-type to G-type AFM phase, the top of valance band shifts from the Z point to Γ point, which makes the original direct band gap become indirect. This can be explained by Slater-Koster parameters using the Harrison approach. The impact of magnetic ordering on band dispersion dramatically changes the optical properties. For the linear ones, the energy shift of the optical band gap could be as large as 0.4 eV. As for the nonlinear ones, the change is even larger. The second-harmonic generation coefficient d33 of G-AFM becomes more than 13 times smaller than that of C1-AFM case. Finally, we propose a practical way to distinguish the two AFM phases of BFO using the optical method, which is of great importance in next-generation information storage technologies.

Surface reconstructions and related local properties of a BiFeO3 thin film

“…The results of our calculations show that BFO still stabilizes in a G-type antiferromagnetic structure in both the type I and the type II surface. This is expected, considering the fact that the magnetic G-type to C-type order transition for BFO films occurs at a c / a ratio of ~1.19 as a result of an increase in compressive lattice strain37. The calculated Fe magnetic moment in the ground state decreases from ~3.8 μ B in the strained film matrix to ~3.0 μ B in the skin unit cell layer for the type I surface.…”

Magnetoelectricity of CoFe2O4 and tetragonal phase BiFeO3 nanocomposites prepared by pulsed laser deposition

“…The more highly aligned ferroelectric polarization in the T-phase BFO may result in better spin alignment in the CFO phase via strain, leading to the enhancement of the magnetization 34 . An exchange coupling should also be considered, where the reorientation of ferroelectric polarization affects the antiferromagnetic spin distribution inside the BFO phase, which could influence the femimagnetic spin arrangement in the CFO 11,24,35 . Similar enhancements were observed when applying a −9V tip bias, for the [001] and ferroelectric polarizations of the T-phase BFO are actually equivalent.…”

“…The T-phase of BFO exhibits unique property characteristics, relative to the R-phase. For example, the antiferromagnetic order in the T-phase changes from G-type (R-phase) to C-type, while the ferroelectric polarization direction rotates from [111] (R-phase) to [001] 21–24 . Here, CFO/T-phase BFO nanocomposites were fabricated on (001) LAO substrates by pulsed laser deposition (PLD), and its ME properties were compared with that of CFO/R-phase BFO ones on (001) SrTiO 3 (STO) substrates.…”

Concepts of the half-valley-metal and quantum anomalous valley Hall effect

“…To assess the dynamical stability of the H-FeCl 2 monolayer under different strains, we calculate their phonon dispersion by using the Quantum-ESPRESSO 50 code. For the optical property calculation, we adopt our own code OPTICPACK, which has been successfully used in various systems 51,52 . To describe the strong-correlated effect of Fe-3d electrons, the Dudarev's approach of the LSDA + U scheme is adopted 53 , in which only the effective U (U eff ) based on the difference between the on-site Coulomb interaction parameter (U) and exchange parameters (J) is meaningful.…”