Figure 1
Illustration: Alan Stonebraker

Figure 1: Multiferroics combine the properties of ferroelectrics and magnets. In the ideal case, the magnetization of a ferromagnet in a magnetic field displays the usual hysteresis (blue), and ferroelectrics have a similar response to an electric field (yellow). If we manage to create multiferroics that are simultaneously ferromagnetic and ferroelectric (green), then there is a magnetic response to an electric field, or, vice versa, the modification of polarization by magnetic field. And, in principle we have here the basis for making a 4-state logic state: (P+M+), (+-), (-+), (--).