  We present a more stringent upper limit on long-range axion-mediated forces
obtained by the QUAX-g$_p$g$_s$ experiment, located at the INFN - Laboratori
Nazionali di Legnaro. We investigate the possible coupling between the electron
spins of a paramagnetic GSO crystal and unpolarized nucleons of lead disks by
measuring variations of GSO magnetization with a dc-SQUID magnetometer. Such an
induced magnetization can be interpreted as the effect of a long-range spin
dependent interaction mediated by axions or Axion Like Particles (ALPs). The
corresponding coupling strength is proportional to the CP violating term
$g_p^eg_s^N$, i.e. the product of the pseudoscalar and scalar coupling
constants of electron and nucleon, respectively. Previous upper limits are
improved by one order of magnitude, namely $g_p^eg_s^N/(\hbar c) \le
4.3\times10^{-30}$ at 95% confidence level, in the interaction range $10^{-3}$
m $<\lambda_a<0.2$ m. We eventually discuss our plans to improve the
QUAX-g$_p$g$_s$ sensitivity by a few orders of magnitude, which will allow us
to investigate the $\vartheta\simeq 10^{-10}$ range of CP-violating parameter
and test some QCD axion models.
