In this article, we report on recent irradiation experiments on magnetic tunnel junctions (MTJ) using either light (C, O) or heavy (Ni) ion beams with energies in the range of 10 MeV/A. For all ions, albeit with different fluence thresholds, the tunnel magnetoresistance decreases irreversibly with increasing ion fluence, with conversely little or no impact on overall resistance. This can only be explained by a modification of the alumina barrier stoechiometry, rather than by interdiffusion. Measurements on irradiated so-called “spin-mirrors” sheet films show that AlOx/metal interface is altered by radiations. Finally, it is shown that MTJs are not a fortiori insensible to swift heavy ion bombardment.

International audienc

The temperature required to set the exchange bias of a ferro∕antiferromagnetic (F∕AF) storage bilayer as a function of the heating pulse width was studied on magnetic tunnel junctions (MTJs) of thermally assisted magnetic random access memories. Heating is produced by a pulse of electric current flowing through the junction. For sufficiently long heating pulse (>20ns), a quasiequilibrium temperature profile is reached in the MTJ. In this stationary regime, a relationship between the temperature of the storage layer and the power of the pulse was established by using an Arrhenius–Néel model of thermal relaxation. The introduction of thermal barriers between the junction tunnel barrier and the electrodes allows a significant reduction of the power required to achieve a given temperature rise of the storage layer. When the heating pulse duration is reduced from 1sto2ns, the heating power required for setting the F∕AF storage bilayer increases by about 80%. This experimental observation is quantitatively interpreted by combining the Arrhenius–Néel model with thermodynamic simulations of heat diffusion with source term given by the experimentally known heating power dissipated in the tunnel barrier by Joule effect.