ferroic

Ferroic is an umbrella term for materials that possess a spontaneous ordering of a property that can be reversed or reoriented by an external field. The core idea is that the ordered state forms domains with different orientations, and switching between these orientations produces characteristic hysteresis in the material’s response. The most common ferroic orders are ferromagnetism, ferroelectricity, and ferroelasticity; materials can also exhibit more than one order, known as multiferroicity.

Ferromagnetic materials display spontaneous magnetization below the Curie temperature. In zero field, magnetic domains align in various directions to minimize energy, but an external magnetic field can reorient these domains. The macroscopic magnetization shows remanence when the field is removed and coercivity when the field is reversed. Ferromagnetism underpins many memory and sensing technologies, including magnets and magnetic random-access memory.

Ferroelectric materials have spontaneous electric polarization below their Curie temperature. Polarization can be reversed by applying an electric field, and a remnant polarization remains after the field is removed, giving rise to a P–E hysteresis loop. Ferroelectrics are used in nonvolatile memory capacitors, actuators, and sensors. Common examples include lead zirconate titanate (PZT) and barium titanate.

Ferroelastic materials exhibit spontaneous strain that can be reoriented by mechanical stress. Domain switching in ferroelastics can produce shape changes and is important in certain actuators and piezoelectric devices. Ferroelastic behavior often accompanies ferroelectricity in many materials, enhancing coupled responses.

Multiferroics describe materials that exhibit two or more ferroic orders simultaneously, enabling coupling between, for example, magnetic and electric properties, with potential applications in novel sensors and memory devices.