Photonic Ferromagnets: Leveraging Chemistry to Develop New Van der Waals Ferromagnets with Strongly Coupled Spin and Optical Functionalities

Materials with strongly coupled electronic, magnetic, and optical properties are highly desirable for application in next-generation spin-based devices. Magnetic van der Waals materials have been demonstrated to be attractive candidates for archetypal spin-based electronics, but such ferromagnets are often non-emissive or show only broad, nondescript luminescence. Moreover, their chemical parameter space is often largely unexplored. This presentation will describe the use of composition to develop new van der Waals materials that both are ferromagnetically ordered <i>and</i> show unique optical properties, with strong coupling between the two. In one example, we show that deliberate doping with optical impurities can transform the broad luminescence of the prototypical 2D ferromagnet, CrI₃, into sharp <i>f-f</i> luminescence of the lanthanide impurity, sensitized by the CrI₃host. We show that the impurity spin is pinned to the ferromagnetism of the CrI₃ lattice, reflecting strong dopant-host exchange coupling and providing sensitive magnetic control over lanthanide emission polarization at exceptionally low fields. In another example, we have developed solution routes to growth of ferromagnetic 2D perovskites with complex compositions. These materials show strongly temperature-dependent absorption whose intensity reflects coupling to thermally populated 2D magnons. We also show that the air stability of these compounds can be increased dramatically through composition tuning. These demonstrations illustrate the ability to leverage the chemical tunability of layered 2D materials to access new and unusual magneto-optical functionalities.