  It was recently discovered that for a boundary system in the presence of a
background magnetic field, the quantum fluctuation of the vacuum would create a
non-uniform magnetization density for the vacuum and a magnetization current is
induced in the vacuum. It was also shown that this "magnetic Casimir effect" of
the vacuum is closely related to another quantum effect of the vacuum, the Weyl
anomaly. Furthermore, the phenomena can be understood in terms of the
holography of the boundary system. In this paper, we generalize this four
dimensional effect to six dimensions. We use the AdS/BCFT holography to show
that in the presence of a 3-form magnetic field strength $H$,a string current
is induced in a six dimensional boundary conformal field theory. This allows us
to determine the gauge field contribution to the Weyl anomaly in six
dimensional conformal field theory in a $H$-flux background. For the (2,0)
superconformal field theory of $N$ M5-branes, the current has a magnitude
proportional to $N^3$ for large $N$. This suggests that the degree of freedoms
scales as $N^3$ in the (2,0) superconformal theory of $N$ multiple M5-branes.
The prediction we have for the Weyl anomaly is a new criteria that the (2,0)
theory should satisfy.
