Inelastic Electron Tunneling Spectroscopy in a Magnetic Molecule Vertical Heterojunction

We have studied the inelastic electron tunneling spectroscopy (IETS) in EGaIn/H₂Pc/MnPc/NCO heterojunctions where sublimated manganese phthalocyanine (MnPc) films as thin as 1 nm (3 layers) are sandwiched between ferrimagnetic bottom-layer NiCo₂O₄ (NCO) and top-layer soft-landing eutectic GaIn (EGaIn) electrodes, and the 1 nm hydrogen phthalocyanine (H₂Pc) is used for the protection layer of MnPc. Through differential conductance measurements dI/dV, we observed conductance jumps at well defined threshold bias voltages, V_th, which indicates the energy exchange between the spins of magnetic molecules and the tunneling electrons. We also investigated the effects of magnetic field and temperature on the heterojunctions and found that they both have large influence on the V_th while the value of dI/dV of each conductance jump remains the same. We attribute the magnetic field dependence to the interaction between MnPc and our ferrimagnetic substrate NCO and attribute the temperature dependence to the correlation effect between tunneling electrons and molecular spins, as reported in a previous STM work [1]. Our work is important for electrical detection of spin qubits in magnetic molecules.

[1] Loth, S., von Bergmann, K., Ternes, M. et al. Controlling the state of quantum spins with electric currents. Nature Phys 6, 340–344 (2010). https://doi.org/10.1038/nphys1616.