Spin-polarized tunnelling, magnetoresistance and interfacial effects in ferromagnetic junctions

The pioneering studies of spin-polarized tunnelling by Meservey and Tedrow in the early 1970s showed that the conduction electrons in ferromagnetic (F M) metals are spin polarized and that the spin is conserved in the tunnelli ng process. Only recently (1995) improved material fabrication techniques h ave permitted realization of the Julliere quantitative model, showing that tunnelling in ferromagnet/insulalor/ferromagnet (FM/I/FM) junctions should lead to a large junction magnetoresistance (JMR); JMR values greater than 3 0% have been achieved at room temperature. This recent success has led to s everal fundamental questions regarding the phenomenon of spin tunnelling an d also the development of JMR devices. In this paper, experimental results, such as the dependence on bias, temperature and barrier characteristics of FM/I/FM tunnelling are reviewed briefly. The influence of inelastic tunnel ling processes, metal at the interface and material properties on the JMR i s discussed. The future direction from both the physics and the application s viewpoints, is also covered.