Proposal for a magnetic-film memory accessed by combined photon and electron beams

A magnetic-film memory accessed by combined photon and electron beams is proposed. The electron beam is used to heat a selected bit, which results in lowering the switching threshold so that information can be written selectively into that bit by means of an external magnetic field. Reading is accomplished by simultaneously illuminating a bit with an electron and a photon beam. Then a thermally modulated magnetic-optical signal is generated by intensity modulation of the electron beam. This arrangement is advantageous since a high-resolution photon beam and photon deflector are not required. The frequency response for thermally modulating a 1-μm bit is calculated to be ∼500 MHz; the necessary temperature dependence of the magneto-optical coefficient and the coercive force can be obtained by using composite films made from layers having different Curie points. Various magneto-optical configurations are readily devised which yield the value of a bit (one or zero) in terms of the phase (0 or π) between the magneto-optical signal and the electron-beam intensity modulation. The shot noise limited signal-to-noise ratio (SNR) is determined by heating of a bit from the photon beam. It is calculated that for a low-loss magnetooptical material such as EuO a 1-μm bit can be read in 1 μs when illuminated with a 1000-μm photon beam. The base-line temperature rise due to heating from the photon beam can be kept small by using narrow pulses of light (width
\sim10^{-11}
second), as, for example, from a mode-locked laser.