  Dynamo models of stellar magnetic fields for partly and fully convective
stars are guided by observational constraints. Zeeman-Doppler imaging has
revealed a variety of magnetic field geometries and, for fully convective stars
in particular, a dichotomy: either strong, mostly axisymmetric, and
dipole-dominated or weak, non-axisymmetric, and multipole-dominated. This
dichotomy is explained by dynamo bistability or by long-term magnetic cycles,
but there is no definite conclusion on the matter. We analysed optical
spectropolarimetric data sets collected with ESPaDOnS and Narval between 2005
and 2016, and near-infrared SPIRou data obtained between 2019 and 2022 for
three active M dwarfs with masses between 0.1 and 0.6 MSun: EV Lac, DS Leo, and
CN Leo. We looked for changes in time series of longitudinal magnetic field,
width of unpolarised mean-line profiles, and large-scale field topology as
retrieved with principal component analysis and Zeeman-Doppler imaging. We
retrieved pulsating (EV Lac), stable (DS Leo), and sine-like (CN Leo) long-term
trends in longitudinal field. The width of near-infrared mean-line profiles
exhibits rotational modulation only for DS Leo, whereas in the optical it is
evident for both EV Lac and DS Leo. The line width variations are not
necessarily correlated to those of the longitudinal field, suggesting complex
relations between small- and large-scale field. We also recorded topological
changes: a reduced axisymmetry for EV Lac and a transition from toroidal- to
poloidal-dominated regime for DS Leo. For CN Leo, the topology remained dipolar
and axisymmetric, with only an oscillation in field strength. Our results show
a peculiar evolution of the magnetic field for each M dwarf, confirming that M
dwarfs with distinct masses and rotation periods can undergo magnetic long-term
variations, and suggesting a variety of cyclic behaviours of their magnetic
fields.
