Autferroicity: Concept, Candidates, and Applications
Magnetism and electric polarity are fundamental physical phenomena whose coupling gives rise to magnetoelectric (ME) effects. Multiferroics, materials hosting simultaneous ferroelectric and magnetic orders, offer cross-control mechanisms but face inherent incompatibility due to the d0 rule versus partially filled d/f orbitals. Improper ferroelectricity, as in h-YMnO3, circumvents this but yields weak polarization (<10 μC/cm2). Type-I multiferroics like BiFeO3 exhibit strong polarization (~100 μC/cm2) but weak ME coupling. This paper introduces autferroicity, a novel ferroic state where ferroelectric and magnetic orders are mutually exclusive, leveraging their repulsive coupling to achieve field-selective switching and strong ME response. Autferroics encode logic states in the identity of the active ferroic phase, enabling high-contrast, low-crosstalk nonvolatile memory. Their bistable energy landscape, reshaped by strong ME coupling, facilitates true random number generation (TRNG) with reduced energy barriers and higher switching frequencies. Practical realization demands advances in synthesis and phase control. Autferroicity offers a paradigm shift, exploiting ferroic exclusivity rather than coexistence, promising robust bistability and intrinsically strong ME coupling for next-generation devices.