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{r}in a sample, since by the proper superposition of ultrasonic pulses with pulse widthLa higher stress state can be generated at{r}than in any other section of the sample. This set of pulses will reduce Hcfrom the unstressed state to H'cc. An applied field H with H'ccwill line up dipoles parallel toHonly 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.