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The University of Southampton

Research project: Joule Heating in Nanowires

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Driven by interest in the proposed Race Track Memory Device there is a lot of research in the motion and pinning of magnetic domain walls in nano wires.

A possible realisation of the Race Track Memory Device is the use of domain walls in magnetic nanowires which are moved by electric currents. However, currently available materials require very large current densities (of the order of 10^12 A/m^2) to drive the domain walls in and this raises the question of the temperature increase in these wires due to the ohmic losses of the current.

It is important to know that the temperature stays below the Curie temperature for the study of magnetic domain wall motion as the ferromagnetism breaks down for greater temperatures and this will affect the interpretation of measured results. It is also a practical challenge to conduct these experiments without accidentally melting or evaporating (i.e. destroying) the sample due to excessive Joule heating from the current, and for use in devices the robustness of this technology will be paramount.

In this project, we compute the increase in temperature of permalloy (Py) nano wires due to high current density. We use multi-physics finite element simulations for detailed spatially and temporally resolved calculations. We study effect of different substrate materials (Si, Si3N4, Diamond) which carry away the heat. We investigate the effect of (2d) substrate membrane versus solid (3d) wafer substrates.

We compare detailed simulation results with an analytical approximative model [2] for 3d substrates. We provide new equation for an estimate of critical time up to which the model by You et al is valid in 3d substrate (equation 5) in [3]. We derive a new equation to compute temperature in nanowire as function of time in 2d substrate (equation 7) in [3].

Some example results are shown in the images, and also available at [4]. Finally, we make electronic tools available to help other groups to compute the analytical expressions using the specific material and geometry parameters in their experiments and devices [4].

[1] Racetrack memory 

[2] Joule heating in nanowires

Related research groups

Computational Engineering and Design
on 3d diamond substrate
Nanowire geometry
after 10^-6 seconds
Temperature profile
see fig 5 in [3]
Heating rate
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