A group of researchers from Hefei Institutes of Physical Science of the Chinese Academy of Sciences (CAS), Hefei University of Technology, South China University of Technology, and University of Science and Technology of China of CAS induced a room-temperature magnetic phase transition from ferromagnetism to antiferromagnetism by intercalating protons into van der Waals ferromagnet Cr_1.2Te₂ nanoflakes. The study was published in Physcial Review Letters and was selected as Editors' Suggestion.

Controlling the direction of magnetization in two-dimensional ferromagnets is vital for developing super-compact, non-volatile spintronic devices. In traditional spintronic devices, the direction of magnetization can usually be switched by a local magnetic field induced by current or by spin transfer torque. However, the high carrier density in van der Waals itinerant ferromagnets is hard to be tuned, which hinders the development of this area.

In this study, the researchers fabricated high-quality single crystals. They found that Cr_1.2Te₂ nanoflakes exfoliated from these crystals exhibited square-shape hysteresis loops at room-temperature, confirming their high practical value.

Further study found that at T=200 K, the magnetism in a 40 nm thick Cr_1.2Te₂ nanoflake exhibited a non-monotonic evolution against the gate voltage with the anomalous Hall resistivity first increasing and then decreasing. When the electron doping concentration n_e=3.8×10²¹cm^-3 at V_g=-14 V, the anomalous Hall resistivity disappeared, revealing a possible magnetic phase transition.

Theoretical analysis showed that the electron-type doping can be achieved in proton-intercalated Cr_1.2Te₂, and a magnetic phase transition from ferromagnetic (FM) to antiferromagnetic (AFM) can be realized with a critical doping concentration of around 10²¹cm^-3, which is consistent with the experimental observations.

This FM-to-AFM phase transition in a van der Waals magnet at room-temperature could lead to improved spintronic devices.