  The magnetic properties of polycrystaline La0.5Ba0.5CoO2.5+d (d = 0.44 and
0.485) where investigated using muon spin relaxation and bulk magnetization
experiments. Below a Curie temperature of T_C = 160 K and 180 K, respectively,
a magnetic phase with a macroscopic ferromagnetic moment forms. muSR proves
that the full volume inhomogeneously orders at T_C but that there is
microscopically a phase separation into phase volumes possessing a fully static
and a slow magnetic dynamic behavior. A peak in the dynamic relaxation rate 35
K respectively 55 K below the Curie temperature indicates the freezing of spin
components. The spin fluctuations are thermally activated with a typical
Jahn-Teller like phonon energy of E_a = 340 K. Together with co-operative
Jahn-Teller distortions appearing below the spin freezing temperature, this
points to a strong magneto elastic coupling as the cause for the magnetic
fluctuations and the spin freezing.
