Small-voltage multiferroic control of two-dimensional magnetic insulators

Magnetic insulators, which have long-range magnetic order and are electrically insulating, allow spin propagation without electron motion and could be used to create dissipationless magnetoelectric and magneto-optical devices. Atomically thin two-dimensional (2D) magnetic insulators could, in particular, be used to fabricate compact devices. However, the efficient electrical control of 2D magnetic insulators remains a challenge due to difficulties in electrostatically doping such insulators and the inability of external electric fields to modify their crystal fields. Here we report the electrical control of the 2D magnetic insulator chromium germanium telluride (Cr₂Ge₂Te₆) using a thin ferroelectric polymer. We show that ±5 V across the Cr₂Ge₂Te₆/polymer heterostructures can open and close the magnetic hysteresis loop. The magnetic modulation is non-volatile, and is observed in bilayer, trilayer and four-layer Cr₂Ge₂Te₆, but not in thicker eight-layer Cr₂Ge₂Te₆, which indicates the importance of the interfacial multiferroic effect. The heterostructure multiferroics also enable direct electrical toggling between two magnetization states.