The defect

the behavior of dynamic and damping motion of domain walls (D.Ws) in some magnetooptic materials have been studied and summarized

e.g. in books

[1

2]

. We noted the Gilbert damping coefficient is an order of 10

-6

and the D.Ws can be moved under the low frequency field of the amplitude value lower 140A/m in the magnetooptic thin film (BiTm)

3

(FeGa)

5

O

12

[3

4]

. In the present paper we report the morphology of D.Ws around the defect in the thin film (BiTm)

3

(FeGa)

5

O

12

under various applied field. The morphology of D.Ws was taken from the home-made polari-microscope-CCD-computer system. From the morphology we can see that:There are two kinds of defect shown in figures

one is like a dark bar in the morphology and the dark bar can not change under applied fields of present experiment

we named it as "hard defect"

it is a intrinsic contaminant; another is a special area located in the convergence of three kinds of D.Ws.

we named it as "configuration". Under the dc field which value is less than 200A/m

the configuration has not been changed almost. Under the ac field which frequency is 1Hz or 10Hz

the configuration is like ellipses sometimes. Under the uniform magnetic field sweeping (d

H

/d

t

=83.6A/m) with ac field (10Hz

the amplitude 140A/m)

the configuration has been changed and the new D.Ws. (made approximately an angle of 120 degree with the parallel D.Ws.

shown in Fig.3(b)) will be presented besides the ellipses configuration sometimes. The configurations in the various applied fields can be discussed as follows. We suppose the orientation of the configuration of three kinds D.Ws. is like the Fig.4 (a) under dc field; the direction of composition motion of the three kinds of D.Ws. is a single one (to the right-down in present experiment). Under ac field

there are opposite amplitude of applied field and the phase difference of moving D.Ws.

it will make the three kinds D.Ws. to separate (or attract)

the area of non-domain walls will be presented. We can see that the photographs shown in Fig.2(a)

(b)

Fig.3(a) have white area at the convergence of the three kinds D.Ws. and the photography shown in Fig.3(b) has a new D.Ws. (made an angle of 120 degree with the parallel D.Ws.).In summary

(1)there is a convergent area of three direction D.Ws.

this area must have a defect

and can be changed to become a white area caused by vanished D.Ws.; (2) around the white area the D.Ws. it can be shaped like ellipses when the applied field is the ac. low frequency field; (3) the new D.Ws. will be presented when the applied field is the uniform magnetic field sweeping with ac field.