We studied zero-field Mn-55 and La-139 nuclear magnetic resonance (NMR) in
La0.5Ca0.5MnO3. The Mn-55 and La-139 NMR intensities, resonance frequencies
, and spin-spin relaxation times showed thermal hystereses upon cooling and
warming. The analysis of the result shows that there are two distinct phas
e regions below T-C: a stable metallic ferromagnetic (FM) region and a regi
on where metallic FM and insulating antiferromagnetic phases compete. The t
wo metallic FM phases are distinguished by mobile e(g) electron density. Th
e e(g) electron density of the stable FM phase is 0.5, but that of the FM p
hase:in the competition region is lower than that. [S0163-1829(99)04945-0].