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Submitted on 1 Jan 1988
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THE STRUCTURE OF A DIFFUSE DOMAIN WALL
IN A BUBBLE GARNET FILM
R. Kosinski
To cite this version:
JOURNAL DE PHYSIQUE
Colloque C8, Supplkment au no 12, Tome 49, dkcembre 1988
R. A. Kosinski
Institute of Physics, Warsaw Techn. University, 00-662 Warsaw, Poland
Abstract. - The structure of a diffise domain wall was investigated numerically for a case of a sample investigaed earlier experimentally by Vural and Humphrey. A number of horizontal Bloch lines occuring simultaneously in the wall, some of them with a large angular span, explain the increase of the effective wall width. Theoretical results agrees very well with the experimental observations.
A diffuse domain wall, was observed firstly by
Zimmer et al. [I] and investigated next by ma* au- thors 12-51. It was found that the wall width A raises with the wall velocity v and depends on value and the orientation of an external in-plane field. In the case of an in-plane field perpendicular t o the wall surface (H,) greater values of A occur than in the case of a parallel in-plane field
(Hz)
[I-41. This phenomenon was ex- plained by a distorsion of the wall surface [I, 2, 41. In the present work numerical computations of the wall motion are performed for the the case of material pa- rameters of the sample used in experiment by Vural and Humphrey (sample 2-16-44) [2], giving the struc- ture of the wall observed experimentally. A descrip-tion of the wall motion was based on the Slonczewski's equation of motion [6] (the form of this equations i s the same as in Eqs. (2, 3) of Ref. [7]. The full implicit numerical sheme with the force free boundary condi- tions was used 171. The calculations were performed for the constant step of the drive field Hz = 135 Oe (with the rise time equal t o 15 ns and the length equal to 400 ns) and the values of the in-plane fields were: Hy = 200 Oe in the case a and
H,
= 200 Oe in the case b as in reference [2] (Fig. 3).As it results from the earlier works on the domain wall dynamics in the presence of an in-plane fields [8, 2, 71 when Hz exceeds the critical value H,,,;t the horizontal Bloch lines (HBLs) appear in the wall and the nonlinear relation v (Hz) occurs 14, 71. It was found in our computations that the value of H,,,;t for the sample 2-16-44 investigated in [2] equals 1.8 Oe. Thus, the value H, = 135 Oe used in experiment [2] corre- sponds t o the nonlinear range of the wall motion and a number of HBLs is supposed t o appear during the wall motion.
standard wall width parameters). The experimental results obtained by Vural and Humphrey [2] for the case a are marked by the vertical lines which show the spread of theese results (experimental results for the case b are not available in Ref. [2]). It can be seen that, in the case a the wall width
A
/
A0 obtained numer-ically increases during the wall motion, what agrees very well with the experiment [2]. Such an increase is due t o the wall structure occuring in the moving wall. Curve (a) in figure 2 shows the wall profile 11, ( z ) at a certain point of time (t = 200 ns) (11,
-
is the az-imuthal angle of the magnetization vector at the Bloch surface of the wall). At this point of time two HBLs are present in the wall: one line with the angular span equal approximately 8 a is lying near the upper sur- face of the film (z = h
/
2) and the second line, which have the dominant influence on the observed width of the wall, with the angular span equal approximately 150 T . A strong tilting of the Bloch surface of the wallaccompanies to such a structure (curve a in Fig. 2b). The structure of the wall obtained for the case b ex- plains why the distinct increase of the wall width is not observed in the experiment for such an orientation of in-plane fields (cuves b in Figs. 2a, b show a typical wall structure for this case at t = 200 ns). In this case the angular span of HBLs is much lower than in the previous case (see curve b in Fig. 2a), moreover, the sense of rotation of magnetization is opposite in each two neighbour lines. The shape of the Bloch surface of the wall corresponding t o such a structure indicates a large deformations, however, such a large tilting as in the previous case do not occur (see curve b in Fig. 2b). Such a structure is typical for the case of H, fields. Some discrepancies between experimental and nu- merical results are cased by the very simple model of the stray fields used in computations 191.
The calculated changes of the average, reduced wall It may be concluded that a large widths of the do- width A
/
A0 (t) during the wall motion are showed in main wall observed in the walls moving in the pres- figure 1 by circles (case a) and crosses (case b), where ence of an in-plane fields perpendicular to the wall are an averaging of A over the film thickness is made, cor- caused by the tilting of the. wall surface accompanying responding t o the experimental situations (A0 is the t o HBLs with large angular spans occuring in the wall.his
work was supported by The Institute of Physics of The Polish Academy of Sciences, Warsaw, Poland.JOURN-4L DE PHYSIQUE
Fig. 1.
-
Averaged wall width/
A as a function of time for perpendicular field Hy (circles) and parallel field H,(crosses) obtained numerically. Experimental results for Hy are shown by vertical lines.
Fig. 2. - (a) the distribution of t h e azimuthal angle of magnetization $ ( z )
,
(b) t h e shape of the Bloch surface of the wallq (2) for t = 200 ns. Curves a: Ha = 0, H y = 200 Oe, curves b: Hz = 200 Oe, H y = 0. 4 - is the instantaneous average wall position.
Acknowledgment
The Author wish t o t h a n k prof. dr A. Sukiennicki for helpfull discussions and the critical reading of the manuscript.
[I] Zimmer, G. J., Morris, T. M., Vural, K. and Humphrey, F. B., Appl. Phys. Lett. 25 (1974) 750.
[2] Vural, K. and Humphrey, F. B., J. Appl. Phys. 51 (1980) 549.
[3] Suzuki, S., Gal, L. and Maekawa, S., Jpn J. Appl. Phys. 19 (1980) 627.
141 Fuji, T., Kumosaki, K. and Inoune, M., J. Appl. Phys. 52 (1981) 2350.
[5] Kleparski, V. G. and Pinter, I., Phys. Status So- lidi 67 (1981) K29.
[6] Slonczewski, J. C., Int. J. Magn. 2 (1972) 85. [7] Kosinski, R. A. and Engemann, J., J. Magn.
Magn. Mater. 50 (1985) 229.
181 De Leeuv, F. H., IEEE Trans. Magn. MAG-9 (1973) 614.
