Current-driven non-linear magnetodynamics in magnetic nano-devices

Spintronis is an emerging electronic technology that is built on interconnections between the electron’s electric charge and its quantum-mechanical spin. The interconnections allow altering the electrical transport properties of magnetic nano-devices by changing the magnetic configuration, and vice versa. It opens up a possibility of denser and faster magnetic memory and logic devices. In this work, we conducted electronic transport studies using nanco-scale point-contacts in CoSiBFeNb, exchange-biased spin valves, and the antiferromagnetic Mott insulator Sr2IrO4 and Sr3Ir2O7. Magnetic domain switching and evidence of spin-transfer torque in CoSiBFeNb were observed. Furthermore, by simultaneously measuring the rectification signal and microwave absorption, we were able to directly compare electrical detection of ferromagnetic resonance and conventional absorption measurements. We found a good agreement between the methods and showed that here the point-contact acts as a nano-scale bolometer, monitoring the absorption of microwave current. Measurements in exchange-biased spin valves showed that parametric resonance can be excited next to ferromagnetic resonance. These non-linear excitations are driven by spin-transfer torque and due to the field-like component shift with applied dc bias. Parametric resonance can potentially be used as a new and faster method to switch the magnetization in magnetic memory and logic devices. Last, we studied electrical transport in Sr2IrO4 and Sr3Ir2O7. Both compounds revealed a decrease in activation energy with increasing dc bias, which was well fitted by a field-effect model and explained by small lattice distortions. Moreover, a small resistive switching due to the transition between meta-stable states at a critical current was observed. High-frequency measurements in Sr3Ir2O7 showed a resonance-like peak structure in the rectification signal as a function of dc bias at sufficiently high microwave power. We attribute these features to magnonics that can be excited in Sr3Ir2O7 when the lattice is distorted in an ac electric field. Our results show that transition metal oxides such as Sr2IrO4 and Sr3Ir2O7 are a new class of materials that allow for modifying band structures via dc and ac currents in spintronic applications.