This work investigates the tunnel junction heating process for micrometer and submicrometer size junctions to be used in a thermally assisted magnetic random access memories write scheme. The time evolution of the heating process was obtained from experimental measurements and numerical thermal simulations. Simulation results show an initial temperature regime at very short pulse widths associated with the intrinsic heating of the junction (adiabatic regime). In this regime, for the same power density, the temperature increase is independent of the junction area. In the studied geometry, for pulse widths around 1 ns and higher an additional heating occurs in the electrical leads (diffusion regime). The write power density is in this case lower for large junction areas. The use of thermal barriers is an effective mean to decrease the power density required for writing and to eliminate its junction area dependence.
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