On–Off Magnetism of Ferromagnetic Metals via Electrochemical Driven Band Filling

Ferromagnetic metals, distinguished by high Curie temperatures and magnetization, are crucial in voltage-controlled magnetism for potential room-temperature applications in low-power multifunctional devices. Despite numerous attempts based on various mechanisms, achieving ideal magnetic modulation in metals remains challenging. This work proposes a new mechanism to control bulk metal magnetism by modulating valence electron filling in spin-polarized bands, leveraging the Slater–Pauling rule in alloys. Fully reversible on–off switching of ferromagnetism is realized in a 70 nm thick Sn–Co alloy film, with a modulation amplitude approaching 40 emu g^–1 within 1.5 V. Operando magnetometry demonstrates superior magnetic modulation with nonvolatility, robust durability with rapid response. Furthermore, this strategy exploits band filling by a nonmagnetic metal’s valence electrons during alloying, showcasing universality confirmed by significant magnetic switching in Sb–Co and Sn–Fe alloys. These results introduce a novel magnetic modulation method in bulk metals and, crucially, suggest a versatile and straightforward design paradigm for magnetic manipulation.