  Faraday tomography observations with the Low Frequency Array (LOFAR) have
unveiled a remarkable network of structures in polarized synchrotron emission
at high Galactic latitudes. The observed correlation between LOFAR structures,
dust polarization, and HI emission suggests a connection to the neutral
interstellar medium (ISM). We investigated this relationship by estimating the
rotation measure (RM) of the warm neutral (partially ionized) medium (WNM) in
the local ISM. Our work combines UV spectroscopy from FUSE and dust
polarization observations from \Planck\ with LOFAR data. We derived electron
column densities from UV absorption spectra toward nine background stars,
within the field of published data from the LOFAR two-meter sky survey. The
associated RMs were estimated using a local magnetic field model fitted to the
dust polarization data of \Planck. A comparison with Faraday spectra at the
position of the stars suggests that LOFAR structures delineate a slab of
magnetized WNM and synchrotron emission, located ahead of the bulk of the warm
ionized medium. This conclusion establishes an astrophysical framework for
exploring the link between Faraday structures and the dynamics of the
magnetized multiphase ISM. It will be possible to test it on a larger sample of
stars when maps from the full northern sky survey of LOFAR become available.
