Multiferroics and magnetoelectric coupling

3 problems

• Direct electrical measurement of polarization in monolayer NiI2

  Partially resolved

  Type-II multiferroics are materials whose spiral spin order itself creates electric polarization. A single atomic layer of NiI2 has been shown to host the spin spiral, but its electric polarization has not been measured directly.

• A single-phase room-temperature multiferroic with strong magnetoelectric coupling

  Open

  BiFeO3 is magnetic and ferroelectric at room temperature but has almost no net magnetization, while materials with strong coupling between the two orders work only at low temperature. No single material yet combines both at room temperature.

• Minimum energy for electric-field reversal of magnetization

  Open

  A magnetoelectric memory bit would compete with transistors only if an electric field can flip its magnetization with very little energy. How small that energy can be in principle, given that the bit must stay stable against heat, is not known.