New research by researchers from the universities in Linköping and Eindhoven have for the first time successfully shown that hypothetical 'particles' that were proposed by Franz Preisach in 1935 actually exist. The scientist's research paper show why ferroelectric materials act as they do.
Ferroelectricity is closely associated with ferromagnetism. Common ferromagnetic materials include iron, cobalt, and nickel. In these materials, the electrons act as small magnets called dipoles with a north and south pole.
Ferroelectric materials have application in hard disks
In a ferroelectric, the dipoles are not magnetic but electric and have a positive and negative pole. These poles are random unless a sufficiently strong field is applied, then the dipoles align with that field.
That field is known as the coercive or critical field. Ferroic materials retain their alignment even when the field is removed; the material is permanently polarized.
To change this alignment, a field at least as strong as the original must be applied in the opposite direction. This phenomenon is known as hysteresis or the idea that a material behaves in accordance with what has happened to it before.
Franz Preisach's model a mystery despite being 80 years old
This property makes these materials perfect for rewritable memory such as being used in hard disks. Despite a model for ferroelectricity and ferromagnetism being developed by the German researcher Franz Preisach as early as 1935.
Scientists have not fully understood the purely mathematical model laid out by Preisach. The model describes ferroic materials as a collection of small independent modules called hysterons.
But scientists have questioned what these are, and the big question of why do ferroelectric materials act as they do? Incredibly the solution has been found by Professor Martijn Kemerink's research group (Complex Materials and Devices at LiU), in collaboration with researchers at the University of Eindhoven.
Collaboratively the researchers studied two organic ferroelectric model systems and found the explanation. It seems that answer sits in the way the molecules of ferroelectric materials relate to each other, they lie on top of each other to form stacks around a nanometre wide and several nanometres long.
"We could prove that these stacks actually are the sought-after hysterons. The trick is that they have different sizes and strongly interact with each other since they are so closely packed. Apart from its own unique size, each stack, therefore ´feels a different environment of other stacks, which explains the Preisach distribution," says Martijn Kemerink.
The insights provided by this latest research can expand the understanding and use of ferroelectric materials both for conventional and multi-bit data storage applications. The research was published in Nature Communications.