  Throughout a complete Electron Spin Resonance (ESR) and magnetization study
of La0.5Ca0.5MnO3, we discuss about the nature of the complex phase-segregated
state established in this compound below T~210 K. Between TN<T<TC, the ESR
spectra shows two lines characteristic of two different magnetic phases. From
the resonance field (Hr) derived for each line we argue that the
incommensurate-charge-ordering phase (ICO) which coexists with
ferromagnetic-metallic (FMM) clusters in this temperature interval, is mainly
paramagnetic and not antiferromagnetic. The FMM/ICO ratio can be tuned with a
relatively small field, which suggests that the internal energy associated with
those phases is very similar. Below TN, there is an appreciable FM contribution
to the magnetization and the ESR spectra indicates the presence of FM clusters
in an antiferromagnetic matrix (canted). Our results show that ESR could be a
very useful tool to investigate the nature of the phase-separated state now
believed to play a fundamental role in the physics of mixed valent manganites.
