Tuning and sensing spin interactions in Co-porphyrin/Au with NH3 and NO2 binding

Controlling spin interactions in magnetic-molecules/metal is essential for spintronic applications. Recent studies showed that using small molecule coordination, one could switch off the spin interactions between magnetic-molecules and metal substrates. However, this control should not be limited to the two-state switching. The strength of spin interaction can be reduced, but not ``off'' by the proper selection of small molecules. To demonstrate this, we considered two contrasting systems, $\mathrm{N}{\mathrm{H}}<sub>3</sub>$ and $\mathrm{N}{\mathrm{O}}<sub>2</sub>$ coordinated to Co-porphyrin/Au(111). In our scanning tunneling microscopy and spectroscopy (STM and STS), Kondo resonance was preserved with weakened spin coupling after $\mathrm{N}{\mathrm{H}}<sub>3</sub>$ coordination. However, it disappeared after $\mathrm{N}{\mathrm{O}}<sub>2</sub>$ coordination, implying ``off'' spin coupling. These observations are explained with our density functional theory calculation results. This study shows that small molecule coordination to magnetic-molecules/metal is a powerful way to control spin interactions at the single-molecule level.