Design parameters of a 3-dimensional ultrasonic pulse controlled memory device with single domain coherently magnetized cobalt, iron and nickel particles in a non-magnetic matrix

The coercive field Hcof single domain particles is stress sensitive. Theory shows that stress alone leads to Hc(stress) = 3λsσ/Isin a uniaxial single domain particle, if the magnetization rotates coherently. λsis the magnetostriction, σ the stress, and Isthe magnetization. It is therefore possible to orient selectively the orientation of magnetic particles in an arbitrary volume element of volume L³- at position in a sample, since by the proper superposition of ultrasonic pulses with pulse width a higher stress state can be generated at than in any other section of the sample. This set of pulses will reduce Hcfrom the unstressed state to H\´c< Hc. An applied field H with H\´c<H <Hcwill line up dipoles parallel to only in this volume elemet. One can "write" into the memory. Since this "line up" leads to a signal in coil surrounding the sample, one can also "read" if the dipole orientation changes in the volume L³, since this leads to an induced voltage in the coil surrounding the sample.