Alejandro Jara

Angular dependence of superconductivity in superconductor/spin-valve heterostructures

We report measurements of the superconducting transition temperature, Tc, in CoO/Co/Cu/Co/Nb multilayers as a function of the angle α between the magnetic moments of the Co layers. Our measurements reveal that Tc(α) is a nonmonotonic function, with a minimum near α=π/2. Numerical self-consistent solutions of the Bogoliubov-de Gennes equations quantitatively and accurately describe the behavior of Tc as a function of α and layer thicknesses in these superconductor/spin-valve heterostructures. We show that experimental data and theoretical evidence agree in relating Tc(α) to enhanced penetration of the triplet component of the condensate into the Co/Cu/Co spin valve in the maximally noncollinear magnetic configuration.

Spin caloritronic nano-oscillator

Energy loss due to ohmic heating is a major bottleneck limiting down-scaling and speed of nano-electronic devices, and harvesting ohmic heat for signal processing is a major challenge in modern electronics. Here, we demonstrate that thermal gradients arising from ohmic heating can be utilized for excitation of coherent auto-oscillations of magnetization and for generation of tunable microwave signals. The heat-driven dynamics is observed in Y3Fe5O12/Pt bilayer nanowires where ohmic heating of the Pt layer results in injection of pure spin current into the Y3Fe5O12 layer. This leads to excitation of auto-oscillations of the Y3Fe5O12 magnetization and generation of coherent microwave radiation. Our work paves the way towards spin caloritronic devices for microwave and magnonic applications.Harvesting ohmic heat for signal processing is one of major challenges in modern electronics and spin caloritronics, but not yet well accomplished. Here the authors demonstrate a spin torque oscillator device driven by pure spin current arising from thermal gradient across an Y3Fe5O12/Pt interface.

Highly Textured IrMn 3 (111) Thin Films Grown by Magnetron Sputtering

Non-collinear spin ground states in metallic antiferromagnets can give rise to anomalous Hall effect, which enables magnetic state readout in antiferromagnetic spintronic devices. Here we report growth of highly textured films of a non-collinear antiferromagnet IrMn3 on MgO(111) substrates by magnetron sputtering. The films consist of epitaxial (111) twin domains rotated by 60 degrees within the film plane. The films exhibit partial L12 ordering that supports the non-collinear T1 spin structure predicted to give rise to anomalous Hall effect. An MgO buffer layer evaporated onto the substrate increases the L12 order parameter from 0.4 to 0.75 but destroys the (111) crystallographic texture.