By Fan Wu, Nicolas Ubrig and Alberto Morpurgo, UNIGE
The discovery of 2D magnets discloses the possibility to combine semiconducting and magnetic functionalities in a broad platform of atomically thin crystals. Most 2D magnets investigated so far, however, exhibit poor –or very anomalous– semiconducting properties, because the width of their electronic bands is extremely narrow (~100 meV). Narrow bandwidths are detrimental for the electrical conduction in semiconductors as they easily result in electron localization, precluding the realization of field-effect transistors. Indeed, in the 2D magnetic semiconductors investigated so far, transistor action was either entirely absent, or extremely poor.
Our work identifies CrPS4 as a 2D magnetic semiconductor with an electronic bandwidth much larger than that of other similar materials . The conduction bandwidth approaches 1 eV and we demonstrate that field-effect transistors based on this material allow gate-tunable transport to be measured down to cryogenic temperature (T = 2 K), well below the magnetic transition temperature TN = 36 K. The devices exhibit a very large, gate-tunable magnetoconductance (reaching 5000%) and allow to map experimentally the magnetic phase diagram of CrPS4 which hosts multiple phase transitions. The most important result of our work is the ability to control the magnetic state electrostatically in few nanometer thick crystals.
Our results identify CrPS4 as an extremely interesting 2D magnet for future investigations. For instance, a single atomic layer of CrPS4 should allow the realization of gate-tunable half-metals, which have been predicted theoretically but not been observed so far. Our work demonstrates that finding 2D magnetic semiconductors with a large electronic bandwidth is a key goal to fully exploit the interplay between magnetic and semiconducting functionality.