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Register a new userElectric-field switching magnetization and spin transfer in ultrathin BiFeO3 film
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Hong-Jian Feng
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First-principles density-functional theory calculations show switching magnetization by 90 degree can be achieved in ultrathin BFO film by applying external electric-field. Up-spin carriers appear to the surface with positive field while down-spin ones to the negative field surface, arising from the redistribution of Fe-t2g orbital. The half-metallic behavior of Fe-3d states in the surface of R phase film makes it a promising candidate for AFM/FM bilayer heterostructure possessing electric-field tunable FM magnetization reversal and opens a new way towards designing spintronic multiferroics. The interface exchange-bias effect in this BFO/FM bilayer is mainly driven by the Fe-t2g orbital reconstruction, as well as spin transferring and rearrangement.
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First-principals calculations show that up-spin and down-spin carriers are accumulating adjacent to opposite surfaces of BiFeO3(BFO) film with applying external bias. The spin carriers are equal in magnitude and opposite in direction, and down-spin carriers move to the direction opposing the external electric field while up-spin ones along the field direction. This novel spin transfer properties make BFO film an intriguing candidate for application in spin capacitor and BFO-based multiferroic field-effect device.
We report the observation of field-induced magnetization of BiFeO3 (BFO) in an ultrathin BFO/La0.7Sr0.3MnO3 (LSMO) superlattice using polarized neutron reflectivity (PNR). Our PNR results indicate parallel alignment of magnetization across BFO/LSMO interfaces. The study showed an increase in average magnetization on increasing applied magnetic field at 10K. We observed a saturation magnetization of 110 pm 15 kA/m (~0.8 {mu}B/Fe) for ultrathin BFO layer (~2 unit cell) sandwiched between ultrathin LSMO layers (~ 2 unit cell), which is much higher than the canted moment (0.03 {mu}B/Fe) in the bulk BFO. The macroscopic VSM results on superlattice clearly indicate superparamagnetic behavior typically observed in nanoparticles of manganites.
Electric field effect on magnetism is an appealing technique for manipulating the magnetization at a low cost of energy. Here, we show that the local magnetization of the ultra-thin Co film can be switched by just applying a gate electric field without an assist of any external magnetic field or current flow. The local magnetization switching is explained by the nucleation and annihilation of the magnetic domain through the domain wall motion induced by the electric field. Our results lead to external field free and ultra-low energy spintronic applications.
Growing demands for the voltage-driven spintronic applications with ultralow-power consumption have led to new interest in exploring the voltage-induced magnetization switching in ferromagnetic metals. In this study, we observed a large perpendicular magnetic anisotropy change in Au(001) / ultrathin Fe80Co20(001) / MgO(001) / Polyimide / ITO junctions, and succeeded in realizing a clear switching of magnetic easy axis between in-plane and perpendicular directions. Furthermore, employing a perpendicularly magnetized film, voltage-induced magnetization switching in the perpendicular direction under the assistance of magnetic fields was demonstrated. These pioneering results may open a new window of electric-field controlled spintronics devices.
Using density functional theory (DFT), we study how the stability of individual magnetic skyrmions in an ultrathin transition-metal film can be controlled via the external electric fields. For applied electric fields of $mathcal{E}$= $pm 0.5$ V/{AA}, we find changes from 8 to 30$%$ of the Heisenberg exchange, the Dzyaloshinskii-Moriya interaction, the magnetocrystalline anisotropy energy, and the higher-order exchange interactions. Based on atomistic spin simulations using the DFT parameters, we find that the energy barriers for electric field assisted skyrmion writing and deleting can vary by up to a factor of three more than the variations of the interactions. This unexpected result originates from the electric field induced shifts of the critical magnetic field, marking the onset of the field-polarized phase, which exhibits metastable skyrmions. The shift leads to an electric field dependent change of the skyrmion radius at a fixed magnetic field and explains the enhanced energy barrier variations.
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