A magnetoresistive tunnel-junction (MTJ) memory element includes a magnetic reference layer (RL), a magnetic free layer (FL), a tunneling barrier layer, which extends between the magnetic RL and the magnetic FL, and a diffusion-blocking layer (DBL), which extends on the magnetic FL. The includes at least one material selected from a group consisting of bismuth (Bi), antimony (Sb), osmium (Os), rhenium (Re), tin (Sn), rhodium (Rh), indium (In), and cadmium (Cd). An oxide capping layer is also provided on the DBL. The oxide layer may include at least one of strontium (Sr), scandium (Sc), beryllium (Be), calcium (Ca), yttrium (Y), zirconium (Zr), and hafnium (Hf).