Magnetoelectric interfaces and spin transport Burton, J. D.; Tsymbal, E. Y.
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
10/2012, Letnik:
370, Številka:
1977
Journal Article
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Engineered heterostructures designed for electric control of magnetic properties, the so-called magnetoelectric interfaces, present a novel route towards using the spin degree of freedom in ...electronic devices. Here, we review how a subset of such interfaces, namely ferromagnet-ferroelectric heterostructures, display electronically mediated control of magnetism and, in particular, emphasis is placed on how these effects manifest themselves as detectable spin-dependent transport phenomena. Examples of these effects are given for a variety of material systems on the basis of ferroelectric oxides, manganese and ruthenium magnetic complex oxides and elemental ferromagnetic metals. Results from both theory and experiment are discussed.
Resonant tunneling via localized states in the barrier can invert magnetoresistance in magnetic tunnel junctions. Experiments performed on electrodeposited Ni/NiO/Co nanojunctions of area smaller ...than 0.01 microm(2) show that both positive and negative values of magnetoresistance are possible. Calculations based on Landauer-Büttiker theory explain this behavior in terms of disorder-driven statistical variations in magnetoresistance with a finite probability of inversion due to resonant tunneling.
Based on first-principles calculations, we demonstrate the impact of the electric polarization on electron transport in ferroelectric tunnel junctions (FTJs). Using a Pt/BaTiO3/Pt FTJ as a model ...system, we show that the polarization of the BaTiO3 barrier leads to a substantial drop in the tunneling conductance due to changes in the electronic structure driven by ferroelectric displacements. We find a sizable change in the transmission probability across the Pt/BaTiO3 interface with polarization reversal, a signature of the electroresistance effect. These results reveal exciting prospects that FTJs offer as resistive switches in nanoscale electronic devices.
First-principles density functional calculations demonstrate that a spin-polarized two-dimensional conducting state can be realized at the interface between two nonmagnetic band insulators. The (001) ...surface of the diamagnetic insulator FeS(2) (pyrite) supports a localized surface state deriving from Fe d orbitals near the conduction band minimum. The deposition of a few unit cells of the polar perovskite oxide LaAlO(3) leads to electron transfer into these surface bands, thereby creating a conducting interface. The occupation of these narrow bands leads to an exchange splitting between the spin subbands, yielding a highly spin-polarized conducting state distinct from the rest of the nonmagnetic, insulating bulk. Such an interface presents intriguing possibilities for spintronics applications.
The discovery of a high-mobility two-dimensional electron gas (2DEG) in wurtzite ZnO/Zn(Mg)O heterostructures is promising for applications due to the high mobility of the carriers. In this paper, we ...study the formation and properties of the 2DEG at ZnO/Zn(Mg)O interfaces using first-principles calculations based on hybrid density functional theory. The 2DEG arises from the polarization discontinuity at the interface between the two materials. The uncompensated bound charge at the interface gives rise to an electric field in the bulk of ZnO which confines free carriers close to the interface. We find that the type of the confined carriers is determined by the interface termination, while the amount of charge and the confinement width could be controlled by the Mg doping and the device dimensions.
Interfaces play a critical role in nanoscale ferroelectricity. We perform a first-principles study of ultrathin KNbO3 ferroelectric films placed between two metal electrodes, either SrRuO3 or Pt. We ...show that bonding at the ferroelectric−metal interfaces imposes severe constraints on the displacement of atoms, destroying the bulk tetragonal soft mode. If the interface bonding is sufficiently strong, the ground-state represents a ferroelectric domain with an interface domain wall, driven by the intrinsic oppositely oriented dipole moments at the two interfaces. The critical thickness for the net polarization of the KNbO3 film is predicted to be about 1 nm for Pt and 1.8 nm for SrRuO3 electrodes.
Spin-orbit coupling (SOC), the interaction between the electron spin and the orbital angular momentum, can unlock rich phenomena at interfaces, in particular interconverting spin and charge currents. ...Conventional heavy metals have been extensively explored due to their strong SOC of conduction electrons. However, spin-orbit effects in classes of materials such as epitaxial 5
-electron transition-metal complex oxides, which also host strong SOC, remain largely unreported. In addition to strong SOC, these complex oxides can also provide the additional tuning knob of epitaxy to control the electronic structure and the engineering of spin-to-charge conversion by crystalline symmetry. Here, we demonstrate room-temperature generation of spin-orbit torque on a ferromagnet with extremely high efficiency via the spin-Hall effect in epitaxial metastable perovskite SrIrO
We first predict a large intrinsic spin-Hall conductivity in orthorhombic bulk SrIrO
arising from the Berry curvature in the electronic band structure. By manipulating the intricate interplay between SOC and crystalline symmetry, we control the spin-Hall torque ratio by engineering the tilt of the corner-sharing oxygen octahedra in perovskite SrIrO
through epitaxial strain. This allows the presence of an anisotropic spin-Hall effect due to a characteristic structural anisotropy in SrIrO
with orthorhombic symmetry. Our experimental findings demonstrate the heteroepitaxial symmetry design approach to engineer spin-orbit effects. We therefore anticipate that these epitaxial 5
transition-metal oxide thin films can be an ideal building block for low-power spintronics.
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