Large Magnetoresistance in a Si-Based Double-Tunnel Junction with Purely Organic Radical Molecules

Organic radicals have shown promise for tunable and low-cost spintronic devices. However, integrating the radicals with a Si metal-oxide-semiconductor (MOS) structure remains a challenge. Here, we incorporate stable (4-(((2,5-bis(2-(phenyl)ethynyl)phenyl)carbonyl)(methyl)amino)-2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl (TEMPO-OPE) radicals in a Si-MOS-based double-tunnel junction and demonstrate a huge positive magnetoresistance of up to 400% at a magnetic field of 7 T and a temperature of 3 K. This goes along with a significant reduction of the differential conductance peak corresponding to the highest occupied molecular orbital (HOMO) of TEMPO-OPE under external magnetic fields. First-principles calculations suggest that the singly occupied molecular orbital can mix with the HOMO of TEMPO-OPE. This could lead to suppression of the HOMO conductance peak under magnetic fields and, thus, provide a possible origin of the large magnetoresistance. These findings suggest a path toward incorporating magnetic molecular functionalities into conventional Si devices, leading to large-scale integration of molecular spintronic devices.