Realization of efficient tuning of the Fermi level in iron-based ferrimagnetic alloys

The Stoner criterion allows only three single elements possessing room-temperature (RT) ferromagnetism: cobalt (Co), nickel (Ni), and iron (Fe). Although these three elements have played central roles in magnetism-based materials, their large work function (4.5 similar to 5.2 eV) is becoming a non-negligible obstacle for realization of spin devices using nonmetallic materials with finite energy gaps, because injection of electron spins into these nonmetallic materials is strongly hampered due to the large Schottky barrier height. Hence, a novel ferromagnetic or ferrimagnetic material simultaneously possessing RT ferromagnetism or ferrimagnetism and high Fermi energy is strongly required. Here, we show that an Fe-based alloy, iron-gadolinium (FeGd), allows circumvention of the obstacle. Surprisingly, only 20% of Gd incorporation in Fe dramatically modulates the Fermi energy from -4.8 to -3.0 eV, which is the largest modulation in all metallic alloys reported thus far. The coexistence of ferrimagnetism and nonzero spin polarization at RT of FeGd supports its abundant potential for future applications in low-carrier-density materials such as monolayer, organic, and nondegenerate inorganic semiconductors.