Spectral line

Quantum mechanics

Magnetic circular dichroism

Raman spectroscopy

Ground state

Stacking

Antiferromagnetism

Materials science

Ferromagnetism

Nuclear magnetic resonance

Crystal structure

Molecule

Magnetism

Thermodynamics

Physics

Organic chemistry

Optics

Astronomy

van der Waals force

Monoclinic crystal system

Hydrostatic pressure

Condensed matter physics

Crystallography

Chemistry

Nature Materials

Stacking order can influence the physical properties of two-dimensional van der Waals materials1,2. Here we applied hydrostatic pressure up to 2 GPa to modify the stacking order in the van der Waals magnetic insulator CrI3. We observed an irreversible interlayer antiferromagnetic-to-ferromagnetic transition in atomically thin CrI3 by magnetic circular dichroism and electron tunnelling measurements. The effect was accompanied by a monoclinic-to-rhombohedral stacking-order change characterized by polarized Raman spectroscopy. Before the structural change, the interlayer antiferromagnetic coupling energy can be tuned up by nearly 100% with pressure. Our experiment reveals the interlayer ferromagnetic ground state, which is established in bulk CrI3 but not observed in native exfoliated thin films. The observed correlation between the magnetic ground state and the stacking order is in good agreement with first principles calculations3-8 and suggests a route towards nanoscale magnetic textures by moiré engineering3,9.

Pressure-controlled interlayer magnetism in atomically thin CrI3