Thermostrictive Recording on Permalloy Films

Where the magnetostrictive coefficient is of the order of 10
⁻⁶
or greater, recording may be accomplished on uniaxial Permalloy films by the application of a local stress in coincidence with a biasing field. Here, the stress is introduced into the film as a result of a temperature gradient produced by an incident laser or electron beam. The mechanism of recording is studied and a model developed in agreement with the mechanism. Several modes of recording are discussed, with the advantages and disadvantages of each. Extrapolating the model to a large capacity memory of 10
⁷
bits per square inch with 8 micron diameter spots on a Permalloy film having a magnetostrictive coefficient of 10
⁻⁵
, a 20°C temperature rise will be experienced with 2 × 10
⁻¹⁰
joules of energy in the beam. The beam power required is 10
⁻³
watts at 10% efficiency and a one megacycle information rate.