Usal: Modelling magnetization dynamics in piezoelectric/magnetic devices

Host: University of Salamanca

Location: Salamanca, Spain

Supervisor: Luis Lopez-Diaz, Eduardo Martinez

Scientific project: The PhD project is focused on studying the effect of strain on the magnetic properties of different materials, nanostructures and devices. The work to be carried out is theoretical and computational, although it will be done in close collaboration with the network partners doing experimental work in this topic. As such, it will require visiting their labs to familiarize with the experiments techniques, help in the interpretation of the data and in the design of new devices.

A significant part of the effort will the devoted to the development and numerical implementation of a mesoscopic model that couples micromagnetics, elastodynamics and electrostatics self-consistently [1]. This will be carried out starting from some preliminar work done by the group in this direction and it will require extensive use of COMSOL Multiphysics for both code validation and some large scale electro-mechanical simulations. Once tested and optimized, the code will be used to investigate how voltage-induced strain can be used to manipulate domain walls efficiently in different ways: reversible pinning/depinning with voltage pulses, channelling their motion via strain gradients, transferring momentum with elastic waves, etc. The development of new magnetoresistive domain wall sensors based on some of these concepts will be explored.

On the other hand, the project also entails investigating the effect of strain on the magnetic properties of a variety of materials and heterostructures at a more fundamental level, namely how exchange, DMI or interface anisotropy are affected by strain. For such study, a multiscale modelling approach will be followed. On one hand, a discrete spin model [2] taking into account the crystal lattice structure and the magnetic moment arrangement at atomistic level, applicable to both ferromagnetic and antiferromagnetic ordering and including all relevant interactions, will be developed. On the other, the intrinsic material parameters for this model (atomistic magnetic moments, exchange matrix, anisotropy, etc.) will be obtained from ab-initio quantum-mechanical approaches based on density functional theory. The ultimate goal of this work will be to investigate efficient ways to reverse the magnetization of ferromagnetic and antiferromagnetic nanostructures with voltage or photo-induced picosecond strain pulses.

[1] C.-Y. Liang et al., J. App. Phys. 116, 123909 (2014).

[2] R. F. L. Evans et al., J. Phys.: Condens. Matter, 26, 103202 (2014).