  In order to investigate the relation between magnetic structures and the
signatures of heating in plage regions, we observed a plage region with the He
I 1083.0 nm and Si I 1082.7 nm lines on 2018 October 3 using the integral field
unit mode of the GREGOR Infrared Spectrograph (GRIS) installed at the GREGOR
telescope. During the GRIS observation, the Interface Region Imaging
Spectrograph (IRIS) obtained spectra of the ultraviolet Mg II doublet emitted
from the same region. In the periphery of the plage region, within the limited
field of view seen by GRIS, we find that the Mg II radiative flux increases
with the magnetic field in the chromosphere with a factor of proportionality of
2.38 \times 10^4 erg cm^{-2} s^{-1} G^{-1}. The positive correlation implies
that magnetic flux tubes can be heated by Alfv'en wave turbulence or by
collisions between ions and neutral atoms relating to Alfv'en waves. Within the
plage region itself, the radiative flux was large between patches of strong
magnetic field strength in the photosphere, or at the edges of magnetic
patches. On the other hand, we do not find any significant spatial correlation
between the enhanced radiative flux and the chromospheric magnetic field
strength or the electric current. In addition to the Alfv'en wave turbulence or
collisions between ions and neutral atoms relating to Alfv'en waves, other
heating mechanisms related to magnetic field perturbations produced by
interactions of magnetic flux tubes could be at work in the plage chromosphere.
