Vortex dynamics in magnetic tunnel junctions as the basis of a novel modulation and demodulation transmission scheme

Abstract

The magnetisation dynamics associated with the free layer of a magnetic tunnel junction (MTJ) have been intensely studied over recent years, giving rise to the idea of a spin-torque nano-oscillator (STNO). Whilst these devices have been shown to have clear technological advantages in terms of tunability, agility, scalability and integration. However, the very advantages that make STNOs exciting in terms of tunability make them unlikely to be integrated with conventional wireless communication paradigms, which operate over very narrow frequency bands. In order for STNOs to have a role to play in data transfer, a new paradigm for the data transmission scheme must be envisaged. In this presentation we focus on using the magnetization dynamics of a vortex-based MTJ specifically as a wideband radio-frequency detector. We will present a thorough investigation of the novel dynamic behaviour in such systems, where the in-plane magnetic field induced by an integrated field line induces the constant nucleation and expulsion of the vortex core. Furthermore, we will show how this behaviour can lead to a strong MTJ resistance dependence on the incoming radio-frequency power and frequency, a behaviour which is well recreated with micromagnetic simulations. The frequency and power dependence of the vortex-based MTJs makes them exciting candidates as wide-band analogue dynamic sensors, which are particularly well suited to the demodulation of information encoded by STNOs. In conclusion we present an STNO-based modulation and demodulation scheme, which can encoded and alphabet of M characters, which has the potential for highly efficient data transfer for use in on-chip communications and autonomous sensor networks.