An overview is given of the state of the art in spin electronics. The technical basis is reviewed and simple ideas of giant magnetoresistance discussed. The connection between spin electronics and mesomagnetism is explored. Three-terminal spinelectronic devices are introduced of various types including hot carrier and hybrid spin/semiconductor devices. Spin-tunnel devices are examined and single spin

The direct impact of the electronic structure on spin-polarized transport has been experimentally proven in high-quality Fe/MgO/Fe epitaxial magnetic tunnel junctions, with an extremely flat bottom Fe/MgO interface. The voltage variation of the conductance points out the signature of an interfacial resonance state located in the minority band of Fe(001). When coupled to a metallic bulk state, this spin-polarized interfacial state enhances the band matching at the interface and therefore increases strongly the conductivity in the antiparallel magnetization configuration. Consequently, the tunnel magnetoresistance is found to be positive below 0.2 V and negative above. On the other hand, when the interfacial state is either destroyed by roughness-related disorder or not coupled to the bulk, the magnetoresistance is almost independent on the bias voltage.

This review is intended as an introduction to mesomagnetism, with an emphasis on what the defining length scales and their origins are. It includes a brief introduction to the mathematics of domains and domain walls before examining the domain patterns and their stability in 1D and 2D confined magnetic structures. This is followed by an investigation of the effects of size and temperature on confined magnetic structures. Then, the relationship between mesomagnetism and the developing field of spin electronics is discussed. In particular, the various types of magnetoresistance, with an emphasis on the theory and applications of giant magnetoresistance and tunnelling magnetoresistance, are studied. Single electronics are briefly examined before concluding with an outlook on future developments in mesomagnetism.

We report on spin-polarized tunneling in fully epitaxial Fe/MgO/Fe/Co tunnel junctions. By increasing the thickness of the insulating layer (tMgO), we have strongly enhanced the tunnel magnetoresistance. Values up to ∼100% at 80 K (∼67% at room temperature) have been observed with tMgO=2.5 nm. This tunnel magnetoresistance ratio, which is much larger than the one predicted by the Jullière’s model, can be understood in the framework of ab initio calculations.

We compare the thermal variations of ESR, dc, and microwave resistivity of unoriented bulk single wall carbon nanotube samples. We conclude that the ''metallic'' high-T behavior (d/dTϾ 0͒ is an intrinsic property of the bulk material, and that the system remains metallic even at low temperature where d/dTϽ 0. The spin susceptibility is also independent of T, and a long mean free path implies transport predominantly along the tube axes in bulk material. ͓S0163-1829͑97͒08440-3͔