Probing fast heating in magnetic tunnel junction structures with exchange bias

Heat diffusion in a magnetic tunnel junction (MTJ) having a ferromagnetic/antiferromagnetic free layer is investigated. The MTJ is heated by an electric current pulse of power P-HP, flowing through the junction in current perpendicular to the plane (CPP) geometry, via Joule heat dissipation in the tunnel barrier. According to a proposed one-dimensional (1D) model of heat diffusion, when an electric voltage is applied to the MTJ, the free layer experiences a transient temperature regime, characterized by an exponential increase of its temperature T-AF with a time constant tau(TR), followed by a steady temperature regime characterized by T-AF = T-RT + alpha P-HP, where T-RT is the room temperature and alpha is a constant. Magnetic transport measurements of exchange bias HEX acting on the free layer allow the determination of alpha and tau(TR). The experimental values of alpha and tau(TR) are in agreement with those calculated using the 1D model and an estimation of the MTJ thermodynamic parameters based on the Dulong-Petit and Widemann-Franz laws.