Electrically tunable moire magnetism in twisted double bilayers of chromium triiodide

Moire superlattices in van der Waals structures can be used to control the electronic properties of the material and can lead to emergent correlated and topological phenomena. Non-collinear states and domain structures have previously been observed in twisted van der Waals magnets, but the effective manipulation of the magnetic behaviour remains challenging. Here we report electrically tunable moire magnetism in twisted double bilayers-that is, a bilayer plus a bilayer with a twist angle between them-of layered antiferromagnet chromium triiodide. Using magneto-optical Kerr effect microscopy, we observe the coexistence of antiferromagnetic and ferromagnetic order with non-zero net magnetization-a hallmark of moire magnetism. Such a magnetic state extends over a wide range of twist angles (with transitions at around 0 & DEG; and above 20 & DEG;) and exhibits a non-monotonic temperature dependence. We also demonstrate voltage-assisted magnetic switching. The observed non-trivial magnetic states, as well as control via twist angle, temperature and electrical gating, are supported by a simulated phase diagram of moire magnetism. The magnetic state of twisted double bilayers of antiferromagnetic chromium triiodide can be controlled by electrical gating, twist angle and temperature.