Physicists for several years have been predicting a new age of semiconductor devices that operate by subtle changes in the orientation of electron spins. Known as "spintronics," the field relies on an intricate knowledge of the magnetic properties of materials and of how magnetic moments can be manipulated.Now, scientists at the California Institute of Technology have developed a novel method of measuring the resistance of "domain walls," which are the nanoscale boundaries separating areas of a magnetized material that possess different magnetic alignments, or a "twist" of magnetic spins.