We investigated the
spin properties of the terbium phthalocyanine
(TbPc) species adsorbed on the superconductor NbSe
2
surface
using scanning tunneling microscopy and spectroscopy. TbPc
2
is a molecule in a class of single-molecule magnets (SMMs), and
the use of superconductor electrodes attracts attention for the application
to the devices using the spin degree of freedom. TbPc is a building
block of TbPc
2
and can reveal the spin component’s
behavior. In the experiment, TbPc species were placed on the surface
of the superconductor NbSe
2
. We measured Yu–Shiba–Rusinov
(YSR) states caused by the interaction between the superconducting
state and magnetic impurity and inelastic tunneling spectroscopy (IETS)
for the spin excitation, below 1 K. We also measured the Kondo state
formed by the magnetic singlet formation. We detected the radical
spin at the ligand position of the TbPc by the presence of the Kondo
peak and demonstrated that the radical spin forms the YSR feature.
In addition, the exchange interaction energy (
E
ex
) between the spins of the radical ligand (Pc) and the center
4f metal atom (Tb
3+
) is determined by using the IETS technique.
E
ex
is a critical parameter that determines the
blocking temperature, below which the sample behaves as an SMM. IETS
results show that the statistical distribution of
E
ex
has peaked at 1.3, 1.6, and 1.9 meV. The energy range
is comparable to the recent theoretical calculation result. In addition,
we show that the energy variation is correlated with the bonding configuration
of TbPc.