multiferroic
/ MUL-tee-fair-OH-ik /
Some materials are ferroelectric — they carry a switchable built-in electric polarization. Others are ferromagnetic — they carry a switchable built-in magnetism, like a fridge magnet. A multiferroic is the rare material that manages to be both at the same time, holding a built-in electric lean and a built-in magnetic lean together in one crystal.
What makes multiferroics genuinely exciting is not just that the two properties coexist, but that they can talk to each other. In the most prized ones, applying an electric field can nudge the magnetism, and applying a magnetic field can nudge the electric polarization — a cross-coupling called the magnetoelectric effect. This link arises because the same off-center atoms or tilted bonds that set the polarization also steer how neighboring magnetic atoms align.
This matters because it dangles a tempting prize: memory and logic devices you could write electrically — cheap and low-power — yet read magnetically, blending the best of both worlds. The honest caveat is that good multiferroics are scarce: the atomic conditions that favor ferroelectricity tend to oppose magnetism, so most known multiferroics work only at very low temperatures or have weak coupling. It is a vibrant research frontier, not yet an everyday technology.
Bismuth ferrite is the workhorse multiferroic studied today: it is both ferroelectric and magnetically ordered at room temperature, and researchers have shown that flipping its electric polarization with a voltage can rotate its magnetic pattern — exactly the electric-controls-magnetism trick the field is chasing.
In bismuth ferrite, a voltage that flips the electric polarization can also turn its magnetism.
Coexisting electric and magnetic order is the bare definition; the truly useful prize is strong magnetoelectric coupling between them, which remains hard to achieve at room temperature.