multiferroics

Multiferroics are materials that exhibit more than one primary ferroic order parameter in the same phase, most commonly ferroelectricity and (anti)ferromagnetism. The coexistence of spontaneous electric polarization and magnetic order enables a coupling between magnetic and electric properties, known as the magnetoelectric effect. This coupling can allow control of magnetism with an electric field or polarization with a magnetic field, offering potential for low-power electronics and novel spintronic devices.

Multiferroics are often categorized as Type I or Type II. Type I multiferroics have separate origins for ferroelectricity and magnetism, typically displaying large electric polarization but weaker coupling between orders and higher transition temperatures. Type II multiferroics have ferroelectricity induced by magnetic order, providing stronger magnetoelectric coupling but usually smaller polarization and lower ordering temperatures.

Mechanisms and materials vary across families. Lone-pair activity on Bi3+ can stabilize polar distortions, as in BiFeO3, a well-studied room-temperature multiferroic. Magnetic order can induce polarization through mechanisms such as exchange striction or the inverse Dzyaloshinskii–Moriya interaction, producing spin-driven ferroelectricity in compounds including TbMnO3 and MnWO4. Structural families commonly include perovskite oxides, hexagonal manganites, and spinels; single-phase multiferroics compete with composite systems that combine separate ferroelectric and magnetic phases.

Applications proposed for multiferroics include magnetoelectric sensors, non-volatile memories, and energy-efficient spintronic devices. Achieving robust room-temperature multiferroicity with strong coupling remains challenging due to competing interactions, leakage currents, and synthesis constraints. Ongoing research explores new materials, thin-film engineering, and heterostructures to enhance coupling and practical performance.

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