Number 126 (Story #4), April 28, 1993 by Phillip F. Schewe and Ben Stein A BIPOLAR SPIN SWITCH , a transistor-like device developed by Mark Johnson of Bellcore, consists of a sandwich of metal---not semiconductor---films, two outer ferromagnetic films with a paramagnetic gold film in between. This device operates as a closed or open switch depending on whether the magnetizations of the magnetic layers are parallel or anti-parallel. According to Johnson, his switch would benefit from further miniaturization; the device's gain increases with decreasing size, and even with nanometer proportions, the all-metal structure would have plenty of electrons to work with. (Science, 16 April 1993.)