Multilayers and Perovskites Rewrite Rules of Resistance

10 years ago, Peter Grünberg of the Jülich Research Center in Germany discovered a metallic structure that did not seem to obey the ubiquitous Ohm's law. He constructed a sandwich of two iron layers separated by a thin film of chromium and found that at constant voltage he could vary the current through it simply by applying a magnetic field. The resistance of the structure was no longer a constant. Even greater changes of resistance in magnetic fields were soon found in complex oxides called manganese perovskites, closely related to high-temperature superconductors. These phenomena offer tantalizing prospects for applications such as reading heads in hard disk drives and digital videotape recorders and commercial devices are coming soon.