Toward next generation magnetic data storage devices
As the physical limits of size-reduction are approached and given that the maximum amount of storage capacity on disk drives is limited by the size of the magnetic particles on the surface of the disk, a phenomenon called ballistic magnetoresistance (BMR) has been gaining interest. BMR refers to a quantum-mechanical effect related to an electron’s intrinsic angular momentum or spin that effectively turns the electron into a tiny compass needle. An increase or decrease in electrical resistance in an applied magnetic field provides a sensing device with dimensions similar to those of the magnetic particles on a disk. Although the field is blooming, numerous contradictions and experimental difficulties exist and scepticism remains. European researchers initiated the ‘Ballistic magnetoresistance in thin film nanocontacts’ (BMR) project to develop state-of-the-art nano-fabrication techniques, to employ them together with thin film deposition to produce thin film nanoconstrictions (essentially wave guides for the electrons) and to study BMR behaviour in these various nanocontacts. Researchers successfully used focused ion beam (FIB) nano-fabrication to produce current-in-plane (CIP) and current-perpendicular-to-plane (CPP) thin film nanoconstrictions and characterised nano-scale spin transport in these devices. Analysis of extensive experimental data could not confirm the existence of BMR in these devices. Rather, experimentally obtained magnetoresistance data related to constriction size contradicted BMR predictions based on current BMR theory. BMR results provide an important contribution to nano-fabrication techniques that could lead to a new generation of transistor devices. In addition, researchers extended experimental data required to test BMR theories and fostered a better understanding and exploitation of quantum-mechanical phenomena. Continued research should open the way to new data storage and spintronic devices and computers, with important implications for the European economy.