We present a consistent theory for the dependence of the magnetic structure
in bulk samples on external static magnetic fields and corresponding exper
imental results. We applied the theory of micromagnetism to this crystal an
d calculated the Bloch wall thickness as a function of external magnetic fi
elds. The theoretical results agree well with the experimental data, so tha
t the Bloch wall thickness of a < 110 > 71 degrees nickel single crystal wa
s definitely determined with some hundred of nanometer.