Alejandro O. Leon

Opportunities for improving disaster management in Chile: a case study

Purpose – This paper seeks to propose measures to improve management of rainfall‐related disasters in Chile.Design/methodology/approach – This research was carried out as a case study in the semi‐arid region of Chile where above‐normal rainy events occur once or twice during some rainy seasons. Measures to improve management are suggested based on theory, field data, and community participation. The method was based on a review of both the scientific literature and the local media; and a semi‐structured survey that was applied to local parties, including the population affected by past disasters. Also, some participatory activities (i.e. workshops) were organized in order to include the community opinions.Findings – Results show that there have been significant advances during the last decade in Chile regarding disaster management. Yet, improvements need to be done at the local level in order to achieve a holistic, proactive and integrative management, including community participation and sharing respons...

Spin-transfer-driven nano-oscillators are equivalent to parametric resonators

The equivalence between different physical systems permits us to transfer knowledge between them and to characterize the universal nature of their dynamics. We demonstrate that a nanopillar driven by a spin-transfer torque is equivalent to a rotating magnetic plate, which permits us to consider the nanopillar as a macroscopic system under a time-modulated injection of energy, that is, a simple parametric resonator. This equivalence allows us to characterize the phases diagram and to predict magnetic states and dynamical behaviors, such as solitons, stationary textures, and oscillatory localized states, among others. Numerical simulations confirm these predictions.

Voltage Control of Rare-Earth Magnetic Moments at the Magnetic-Insulator–Metal Interface

The large spin orbit interaction in rare earth atoms implies a strong coupling between their charge and spin degrees of freedom. We formulate the coupling between voltage and the local magnetic moments of rare earth atoms with partially filled 4f shell at the interface between an insulator and a metal. The rare earth-mediated torques allow power-efficient control of spintronic devices by electric field-induced ferromagnetic resonance and magnetization switching.The large spin-orbit interaction in the lanthanides implies a strong coupling between their internal charge and spin degrees of freedom. We formulate the coupling between the voltage and the local magnetic moments of rare-earth atoms with a partially filled 4f shell at the interface between an insulator and a metal. The rare-earth-mediated torques allow the power-efficient control of spintronic devices by electric-field-induced ferromagnetic resonance and magnetization switching.

Oscillating decorated interfaces in parametrically driven systems

Macroscopic systems forced by the temporal modulation of their parameters exhibit complex interfaces between symmetric states. Here we investigate the origin of the transition from a flat to an oscillating decorated interface. Based on a model that describes a magnetic plane under the influence of an oscillating magnetic field and an extended Josephson junction under the influence of an alternating current, we derive a simple model that accounts for the interface dynamics. Analytically this model allows us to reveal that this transition is a parametric resonance between the frequencies of interface modes and the forcing. Numerical simulations of magnetic systems, extended Josephson junctions, and our simplified model show quite good agreement.

Parametric Phenomena in Magnetic Nanostripes

Systems with a time-modulated injection of energy self-organize into patterns and solitons. Magnetic systems forced by a direct spin-polarized current and a constant external field are equivalent to parametrically driven systems. This parametric equivalence implies that both systems are described by the same model, the parametrically driven, damped nonlinear Schrodinger equation, and that they exhibit the same parametric phenomena, which includes patterns and solitons. We review here recent literature on the topic, and we investigate the case of long and narrow magnets. This configuration reduces significantly the critical currents at which self-organization emerges, and it allows the formation of bound states of solitons.