Magnetic tunnel junctions (MTJs) are the fundamental storage elements in magnetic random access memory. A MTJ consists of two ferromagnetic (FM) layers separated by an ultrathin insulating layer, with a thickness of a few nanometers. The tunneling current in MTJ depends on the relative orientation of magnetizations of the two FM layers, which can be changed by an applied magnetic field. Nowadays, MTJs are based mostly on transition-metal FM electrodes and Al2O3 barriers. These can be fabricated with reproducible characteristics and with tunnel∗ corresponding author; e-mail: marco. fanciulli@ mdm. infm. it