  Here, we present a study of the influence of microstructure on the magnetic
properties of polycrystalline samples of the La1.5Sr0.5CoMnO6 double
perovskite, with primary attention to the spontaneous exchange bias effect, a
fascinating recently discovered phenomena for which some materials exhibit
unidirectional magnetic anisotropy after being cooled in zero magnetic fields.
By sintering La1.5Sr0.5CoMnO6 at different temperatures, we obtained samples
with distinct average grain sizes, ranging from 1.54 to 6.65 mu_m. A detailed
investigation of the material's structural, morphologic, electronic, and
magnetic properties using X-ray powder diffraction, powder neutron diffraction,
X-ray absorption near edge structure spectroscopy, scanning electron
microscopy, and AC and DC magnetometry has revealed a systematic enhancement of
the exchange bias effect with increasing the average grain size. This evolution
is discussed in terms of changes in the material's porosity and grain
morphology and its influence on the exchange couplings at the magnetic
interfaces.
