Large exchange bias field in a fully van der Waals heterostructure with perpendicular magnetic anisotropy*

New generation spintronics devices have attracted a lot of interest for their ultra-low power and high-speed applications. The discovery of 2D magnets boosted this field beyond the limitations drawn by standard materials in terms of scalability and engineering of multifunctional heterostructures.

Together with perpendicular magnetic anisotropy (PMA) that guarantees better performances in terms of scalability than in-plane (IP) systems, exchange bias (EB) plays a fundamental role in spin valves. It consists in the pinning of one of the two ferromagnetic (FM) layers by an adjacent antiferromagnetic (AFM) one, keeping the other one free. Exploiting 2D materials, while tunneling magnetic junctions with PMA were realized with Fe₃GeTe₂, EB was measured in IP systems only.

In this work, we fabricated heterostructures composed by an even number of layers of CrI₃ and few layers of CrBr₃. CrI₃ is an A-type AFM with spins aligned along the c axis with a metamagnetic transition around 750 mT, while CrBr₃ is a FM that shows PMA with a coercive field of 25 mT. Taking advantage of the different transitions that govern the dichroic spectra of the two materials, we disentangled the responses of the two flakes measuring a large EB of 15 mT that can be reached either by field cooling or initializing the AFM ground state of CrI₃ with a sufficiently large magnetic field. We succeeded to probe the effect down to the bilayer/bilayer limit.

These results open new possibilities to the realization of ultracompact and fully van der Waals spin valves with PMA and strong EB field, paving the way to next generation spintronics devices.