Detection of Hysteretic Magnetism of Manganese Phthalocyanine in a Vertical Tunnel Heterojunction

We have studied the magnetism of manganese phthalocyanine (MnPc) in EGaIn/MnPc/Pt heterojunctions where sublimated crystalline MnPc films as thin as 1 nm are sandwiched between non-magnetic bottom-layer Pt and top-layer soft-landing eutectic GaIn (EGaIn) electrodes. Using tunneling magnetoresistance measurements under external magnetic field sweeps, we observed resistance peaks at the temperature-dependent coercive fields of MnPc. The hysteretic behavior indicates a ferromagnetic coupling between MnPc molecules with a magnetic easy axis perpendicular to the substrate surface. As the temperature is decreased to 2K, well below Tc, the superconductivity transition temperature of the EGaIn electrode, the magnetoresistance shows pronounced features that are consistent with the appearance of laminar and tubular topology associated with the intermediate state of the superconducting EGaIn [1]. A similar behavior was observed in TbPc₂ molecules deposited on superconducting Pb(111) surfaces [2]. Our work illustrates the interaction of crystalline magnetic molecules (MnPc) with the superconducting phases of adjacent electrodes and promises spintronic or spin qubit device applications.

[1] Prozorov, R. Equilibrium topology of the intermediate state in type-I superconductors of different shapes. Phys. Rev. Lett. 98, 257001 (2007).

[2] Serrano, G., Poggini, L., Cucinotta, G. et al. Magnetic molecules as local sensors of topological hysteresis of superconductors. Nat. Commun. 13, 3838 (2022).