University of Arkansas physicists Ivan I. Naumov, Laurent M. Bellaiche, Sergey A Prosandeev, Inna V Ponomareva and Igor A. Kornev reported in 2004 a new phase in tiny nanodisks and nanorods that potentially may enable researchers to increase memory storage by more than one thousand fold. The discovery earned U.S. Patent 7,593,250 in September 2009. The minimum size, i.e., the diameter, of the nanodisks that display bi-stable toroid moments is demonstrated to be 2.8 nanometers (nm). Using the vortex states as discovered in this invention, the ultimate storage density of this approach reaches 80 Terabits per square inch. The storage density achieved by the nanodisks far exceeds the current storage capability of 1 GBits per square inch using magnetic recording. This value is five orders of magnitude higher than that using the conventional approach by use of macroscopic polarization.
The invention, assigned to the Board of Trustees of the University of Arkansas, increases the data storage capability of non-volatile ferroelectric random access memory (NFERAM) using the newly discovered multiple degenerate states formed by ordered toroid moments in low dimensional nanoscale ferroelectric structures. For instance, at low temperature, ferroelectric nanodisks of lead zirconium titanate (PZT) exhibit two robust bi-stable states with clockwise or counterclockwise concentric vortex rings, and these states with opposite toroid moments can be used as the logic states to store "0" and "1" in memory devices. This approach is drastically different from--and superior to--the conventional approach where macroscopic polarization is used. In fact, macroscopic polarization does not exist in the nanodisks and thus cannot be utilized for the purpose of memory devices.
Storing data using toroid moments offers superiority over using the usual polarization in many respects. The multi-stable states of different toroid moments in researchers approach can be conveniently switched by time-dependent magnetic fields. The latter does not require electrode contact which is challenging to make in nanoscale devices. The scientists also found that the toroid moments can be switched by application of inhomogeneous electric fields
In addition to its use in NFERAMs, the discovery of ferroelectricity in nanoparticles may be used for piezoelectric sensors, efficient actuators, nano-scale dielectric capacitors for energy storage, and nano-scale ultrasounds for medical use.
Ferroelectric materials possess spontaneous dipoles, or charge separations, that allow them to create the images seen in medical ultrasound and naval sonar, and also are used to convert signals to sound in cell phones and other audio devices. How these dipoles behave when the material is on the nanoscale is not well known.