  We have measured high-field magnetization and magnetoresistance of
polycrystalline samples of the A-site ordered perovskite CaCu3Ti4-xRuxO12 (x=0
- 4) utilizing a non-destructive pulsed magnet. We find that the magnetization
for x=0.5, 1.0 and 1.5 is nonlinear, and tends to saturate in high fields. This
is highly nontrivial because the magnetization for x=0 and 4 is linear in
external field up to the highest one. We have analyzed this field dependence
based on the thermodynamics of magnetic materials, and propose that the
external fields delocalize the holes on the Cu2+ ions in order to maximize the
entropy. This scenario is qualitatively consistent with a large
magnetoresistance of -70% observed at 4.2 K at 52 T for x=1.5.
