ferroelectric
/ FAIR-oh-ee-LEK-trik /
Most insulators only show polarization while you hold a field on them; turn the field off and they go neutral. A ferroelectric is different and stranger: it carries a built-in polarization all on its own, and you can flip the direction of that polarization with a strong enough field and it will stay flipped. It's like a switch that remembers which way you last threw it.
Inside a ferroelectric crystal, the atoms settle into a slightly off-center arrangement that leaves a permanent tug of charge in one direction — a spontaneous polarization. An applied field can push the atoms over into the mirror-image arrangement, reversing the polarization, and there they stay until pushed back. Heat it past a special temperature, the Curie point, and the off-center order melts away, leaving an ordinary dielectric.
This matters because that switchable, remembered polarization makes ferroelectrics ideal for memory chips, and their huge dielectric response makes them prized for capacitors and sensors. The name is the common confusion: 'ferro' comes from iron because the behavior echoes magnets, but ferroelectrics contain no iron and have nothing to do with magnetism — the analogy is to the flip-and-remember behavior, not the material.
In a ferroelectric memory chip, each tiny cell stores a one or a zero simply by which way its built-in polarization points. Reading or rewriting a bit means nudging that polarization to flip — and because it stays put when the power is cut, the chip remembers its data with no battery.
A ferroelectric memory cell stores a bit in the direction of its built-in polarization.
Despite the 'ferro' in its name, a ferroelectric contains no iron and is not magnetic — the word borrows the analogy with ferromagnets, whose magnetization can likewise be flipped and remembered.