Magnetic tunnels junctions for all-oxide spin valves devices

Surface Recombination in Ultra-Fast Carrier Dynamics of Perovskite Oxide La0.7Sr0.3MnO3 Thin Films

Aspects of the optoelectronic performance of thin-film ferromagnetic materials are evaluated for application in ultrafast devices. Dynamics of photocarriers and their associated spin polarization are measured using transient reflectivity (TR) measurements in cross linear and circular polarization configurations for La_0.7Sr_0.3MnO₃ films with a range of thicknesses. Three spin-related recombination mechanisms have been observed for thicker films (thickness of d ≥ 20 nm) at different time regimes (τ), which are attributed to the electron-phonon recombination (τ < 1 ps), phonon-assisted spin-lattice recombination (τ ∼ 100 ps), and thermal diffusion and radiative recombination (τ > 1 ns). Density functional theory (DFT+U) based first-principles calculations provide information about the nature of the optical transitions and their probabilities for the majority and the minority spin channels. These transitions are partly responsible for the aforementioned recombination mechanisms, identified through the comparison of linear and circular TR measurements. The same sets of measurements for thinner films (4.4 nm ≤ d < 20 nm) revealed an additional relaxation dynamic (τ ∼ 10 ps), which is attributed to the enhanced surface recombination of charge carriers. Our DFT+U calculations further corroborate this observation, indicating an increase in the surface density of states with decreasing film thickness which results in higher amplitude and smaller time constant for surface recombination as the film thickness decreases.

Bidimensional perovskite systems for spintronic applications

The half-metallic behavior of the perovskite Sr₂FeMoO₆ (SFMO) suggests that this material could be used in spintronic applications. Indeed, SFMO could be an attractive material for multiple applications due to the possibility that its electronic properties could be changed by modifying its spatial confinement or the relative contents of its constituent transition metals. However, there are no reports of theoretical studies on the properties of confined SFMOs with different transition metal contents. In this work, we studied the electronic properties of SFMO slabs using spin-polarized first-principles density functional theory along with the Hubbard-corrected local density approximation and a supercell scheme. We modeled three insulated SFMO slabs with Fe:Mo atomic ratios of 1:1, 1:0, and 0:1; all with free surfaces parallel to the (001) crystal plane. The results show that the half-metallicity of the SFMO is lost upon confinement and the material becomes a conductor, regardless of the ratio of Fe to Mo. It was also observed that the magnetic moment of the slab is strongly influenced by the oxygen atoms. These results could prove useful in attempts to apply SFMOs in fields other than spintronics. Graphical abstract Losing the metallic behaviour: density of states changes, around the Fermi level, due to the Fe/Mo ratio for bidimensional perovskite systems.