Spin-dependent electronic transport through multiferroic Co/PbTiO$_{3}$/Co tunnel junctions is studied theoretically. Conductances calculated within the Landauer-Buttiker formalism yield both a large tunnel magnetoresistance (TMR) and a large tunnel
electroresistance (TER). On top of this, we establish a four-conductance state. The conductances depend crucially on the details of the electronic structure at the interfaces. In particular, the spin polarization of the tunneling electronic states is affected by the hybridization of orbitals and the associated charge transfer at both interfaces. Digital doping of the PbTiO$_{3}$ barrier with Zr impurities at the TiO$_{2}$/Co$_{2}$ interface significantly enhances the TMR@. In addition, it removes the metalization of the barrier.
We investigated theoretically electronic and magnetic properties of the perovskite material SrCoO$_{3-delta}$ with $deltaleq 0.15$ using a projector-augmented plane-wave method and a Greens function method. This material is known from various experim
ents to be ferromagnetic with a Curie temperature of 260$,$K to 305$,$K and a magnetic moment of 1.5${,mu_text{B}}$ to 3.0${,mu_text{B}}$. Applying the magnetic force theorem as it is formulated within Greens function method, we calculated for SrCoO$_{3-delta}$ the magnetic exchange parameters and estimated the Curie temperature. Including correlation effects by an effective $U$ parameter within the GGA$+U$ approach and verifying this by hybrid functional calculations, we obtained the Curie temperatures in dependence of the oxygen deficiency close to the experimental values.
Two years after the prediction of a giant spin Hall effect for the dilute Cu(Bi) alloy [Gradhand et al., Phys. Rev. B 81, 245109 (2010)], a comparably strong effect was measured in thin films of Cu(Bi) alloys by Niimi et al. [Phys. Rev. Lett. 109, 15
6602 (2012)]. Both theory and experiment consider the skew-scattering mechanism to be responsible, however they obtain opposite sign for the spin Hall angle. Based on a detailed analysis of existing theoretical results, we explore differences between theory and experiment.
