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 H
c
of single domain particles is stress sensitive. Theory shows that stress alone leads to H
c
(stress) = 3λ
s
σ/I
s
in a uniaxial single domain particle, if the magnetization rotates coherently. λ
s
is the magnetostriction, σ the stress, and I
s
the magnetization. It is therefore possible to orient selectively the orientation of magnetic particles in an arbitrary volume element of volume L
³
- at position
\overrightarrow{r}
in a sample, since by the proper superposition of ultrasonic pulses with pulse width
L
a higher stress state can be generated at
\overrightarrow{r}
than in any other section of the sample. This set of pulses will reduce H
c
from the unstressed state to H'
c
< H
c
. An applied field H with H'
c
c
will line up dipoles parallel to
H
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 L
³
, since this leads to an induced voltage in the coil surrounding the sample.