We report on efficient spin polarized injection and transport in long $\left({10}^2\text{nm}\right)$ channels of ${\text{Alq}}_3$ organic semiconductor. We employ vertical spin valve devices with a direct interface between the bottom manganite electrode and ${\text{Alq}}_3$, while the top-electrode geometry consists of an insulating tunnel barrier placed between the “soft” organic semiconductor and the top Co electrode. This solution reduces the ubiquitous problem of the so-called ill-defined layer caused by metal penetration, which extends into the organic layer up to distances of about 50–100 nm and prevents the realization of devices with well-defined geometry. For our devices the thickness is defined with an accuracy of about 2.5 nm, which is near the ${\text{Alq}}_3$ molecular size. We demonstrate efficient spin injection at both interfaces in devices with 100- and 200-nm-thick channels. We solve one of the most controversial problems of organic spintronics: the temperature limitations for spin transport in ${\text{Alq}}_3$-based devices. We clarify this issue by achieving room-temperature spin valve operation through the improvement of spin injection properties of both ferromagnetic/${\text{Alq}}_3$ interfaces. In addition, we discuss the nature of the inverse sign of the spin valve effect in such devices proposing a mechanism for spin transport.

The magnetic behavior of the perpendicular exchange-spring bilayer and multilayer, constituted of a hard and a soft phase that are exchange-coupled on a nanometric scale, is analyzed by a one-dimensional micromagnetic model leading to a complete magnetic phase diagram in terms of layer thicknesses. The validity of the one-dimensional assumption for the perpendicular situation is demonstrated. The phase diagram provides information on the type of demagnetization processes and the critical fields at which nucleation and reversal take place, depending on the intrinsic properties of the chosen soft and hard materials. An analytical expression of the reversal field is deduced for relatively large thicknesses. Moreover, the effect of a reduced interlayer coupling is also taken into account, leading to slight modifications of both the magnetic phase diagram and the hysteresis loops. A series of $\mathrm{Fe}∕\mathrm{Fe}\mathrm{Pt}$ bilayers, prepared by sputtering, has been used to evaluate the predictions of the model, which has also been tested with the available literature data on $\mathrm{Fe}\mathrm{Rh}∕\mathrm{Fe}\mathrm{Pt}$ bilayers. Both systems have a particular relevance for potential applications in magnetic recording as well as magnetic microelectromechanical systems.

We have prepared perpendicular hard/soft bilayers made of a 10nm L10-FePt layer, which has been epitaxially grown on MgO(100) and a Fe layer with thicknesses of 2 and 3.5nm. The control of the interface morphology allows to modify the magnetic regime at fixed Fe thickness (from rigid magnet to exchange-spring magnet), due to the nanoscale structure effect on the hard/soft coupling and to tailor the hysteresis loop characteristics. Despite the small thickness of the soft layer, the coercivity is strongly reduced compared to the hard layer value, indicating that high anisotropy perpendicular systems with moderate coercivity can be easily obtained.