  High energy resolution spectroscopic studies of quantum magnets have proven
to be extremely valuable in directly accessing magnetodynamics quantities, such
as energy barriers, magnetic interactions, lifetime of excited states and
fluctuations at the most fundamental level. Here, we explore the existence of a
new flavor of low-energy spin-excitations for quantum spins coupled to an
electron bath. In sharp contrast to the usual tunneling signature of two steps
symmetrically centered around the Fermi level, we find a single step in the
conductance. Combining time-dependent and many-body perturbation theories,
magnetic field-dependent tunneling spectra are explained to be the result of an
interplay between weak magnetic anisotropy energy, magnetic interactions and
Stoner-like electron-hole excitations that are strongly dependent on the
magnetic states of the studied nanostructures. We additionally map the
evolution of the conductance peak in artificial nanostructures crafted
atom-by-atom, which show clear evidence of spin-coupled behavior. The results
are rationalized in terms of a non-collinear magnetic ground state and the
dominance of ferro- and antiferromagnetic interactions. The atomically crafted
nanomagnets offer an appealing model for the exploration of electrically pumped
spin systems.
