New stable state of bubbles containing Bloch lines

A new kind of bubble having two stable states for a bias field H
B
has been found in thin garnet films. The bubble becomes smaller with increasing H
B
and disappears abruptly at some critical field
H_{C1}
. However, it does not collapse at
H_{C1}
. When H
B
is lowered, it comes into sight suddenly at another critical field
H_{C2}
. This means that for H
B
between
H_{C1}
and
H_{C2}
the bubble has two stable states, one for a large bubble and the other for an unobservably small bubble. This has been well explained in terms of the stability of bubbles containing a definite number of Bloch lines.