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Domains and crystal defects in flux-grown gallium-substituted YIG single crystals
DOMAINS AND CRYSTAL D E F E C T S IN F L U X - G R O W N G A L L I U M - S U B S T I T U T E D YIG S I N G L E CRYSTALS C. MAZURI~-ESPEJO, M. S C H L E N K E R , * J. BARUCHEL, J. C. PEUZIN** and J. DAVAL** Laboratoire Louis Neel du CNRS, associe h I'USMG, 166 X, 38042 Grenoble-Cedex, France
Magnetic domains and crystal defects were investigated in a crystal of GaxY3Fes_~O]2. Strong interaction was observed between dissolution striations and the magnetization, leading to a characteristic domain configuration involving long range stress creating domain walls pinned to the striations.
The low saturation magnetization of galliumsubstituted yttrium iron garnet, (Ga) YIG, makes it a valuable material for microwave applications. The present study was undertaken in an effort to elucidate the origin of parasitic resonance modes sometimes encountered in spheres of GaxFes_xY3Ol2, with x ~ 1, impairing the device performance. The crystals were grown in closed crucibles in a PbO-PbF2-B203 flux slowly cooled from 1270 to 1000°C. Flux-grown crystals usually feature growth striations, delineating the natural faces at various stages of growth; their orientation is normal to the growth direction and remains constant within the volume (growth sector) generated by a single natural face. The results discussed in the present paper were obtained using a 100 ~m thick plate parallel to (011), hence containing four easy magnetization directions and mainly consisting of a growth sector where the growth direction, [211], was also parallel to the specimen surface. The sample was mechanically polished, but chemical etching in hot phosphoric acid proved necessary in addition in order to obtain X-ray topographs revealing crystal defects and simple ferrimagnetic domain structures [1]; the surface scratches which then became visible in optical examinations are completely invisible on X-ray topographs, and therefore seem to create no strain. Fig. 1 shows the magnetic domain pattern observed with the Faraday effect using slightly tilted illumination. Simple 180 ° domains with in-plane magnetization in the top region exhibit closure domains reminiscent of the edge of a crystal; the lower half of the picture reveals an alternation of bands nor*Also: Institut Laue-Langevin, 156 X, 38042 Grenoble-C~dex, France. **LETI, CENG, 85 X, 38041 Grenoble-C~dex, France.
1322
mal to the growth direction, changing direction at a growth sector boundary (fig. 2b), obviously involving out-of-plane magnetization directions, and of domains with magnetization in the surface and parallel to these bands. Such strong-contrast bands were found to reproduce consistently at the very same locations after being destroyed by a magnetic field. Close examinations in non-polarized light (fig. 2a) as well as X-ray transmission topographs (fig. 2c) indicate, at these locations, the presence of striations. The characteristic curved shape they take at the growth sector boundary (fig. 2a) makes it possible to identify them as dissolution striations [2-4] produced during the growth of the crystal by a temporary
Fig. 1. Magnetic domain pattern of the (011) plate.
Journal of Magnetism and Magnetic Materials 15 - ! 8 (1980) 1322-1324 ©North Holland
C. Mazur~-Espejo et al./ Domains and crystal defects in flux grown GaYIG
1323
C Fig, 2. (a) Dissolution striations observed in nonpolarized light and Co) the corresponding domain bands changing direction at the growth sector boundary. X-ray transmission topographs of the same region: (c) 088 reflection; (d) 444 reflection.
regression of growth followed by a fast catchingup, due to a large temperature fluctuation. It is to be noted that only some of the optically visible striations are decorated with out-of-plane domain bands; on X-ray topographs made in a magnetic field in order to eliminate domain-wall contrast and using a (444) reflection, on which ordinary growth striations in the [211] sector are practically invisible, they retain a rather strong contrast (fig. 2d), indicating they are associated with more complicated lattice distortions. Close observation of the strong-contrast domain bands using the Faraday effect leads, for the simpler type with noncorrugated walls, to the pattern of magnetization distribution shown in fig. 3,
giving a cross section parallel to a (117) plane. It may be noted that, at least in this schematic model, this domain structure is stray-field-free, but involves several walls that give rise to long-range stresses [5, 6]: this domain structure would therefore be unstable in a perfect crystal, and the central, stress-creating (211) wall is probably pinned to the striation largely through interactions with its strain field. A similar situation was encountered earlier in terbium iron garnet [7], although there the resulting domain structure involved stray-fields and was observed only in a magnetic field. In the present case, a dissolution striation forces the magnetization direction to be parallel to it
1324
C. Mazur~-Espejo et al./ Domains and crystal defects in flux grown GaY1G
011
@2)
/'
"~1~
2~1) y"',,,, ®
/
\
_
.
111 =
)
~ ~ 1 1 ~
o~v / I X
/ [11iF
[/'~I~\
/
/// ® ~211
Q . , ,400Hn~ Fig. 4. Reference directions and scale.
Fig. 3. Pattern of magnetization distribution for the simpler domain bands; (111) section.
outside the band-domains shown in fig. 3, thus causing the occurrence of closure domains at some distance as is seen in fig. 1. It therefore has, at least in the statical behaviour of the particularly simple geometry we have investigated, a very strong effect, comparable to that of a free surface. For reference directions and scale see fig. 4. The authors are happy to thank A. Mathiot and R. de Tournemine for their friendly cooperation, and F. Lefaucheux and M. C. Robert for an illuminating discussion.
References
[1] J. Basterfield, J. Appl. Phys. 39 (1968) 5521. [2] J. P. M. Damen and J. M. Robertson, J. Crystal Growth 16 (1972) 50. [3] R. Hergt, M. Wendt, P. Gornert and S. Bormann, Phys. Star. Sol. (a) 35 (1976) 347, [4] S. Gits-L~on, M. C. Robert and A. Zarka, Bull. Mineral 101 (1978) 399. [5] G. Rieder, Abb. Braunschw. Wiss. Ges. 11 (1959) 20. [6] M. Klernan and M. Schlenker, J. Appl. Phys. 43 (1972) 3184. [7] J. Linares-Galvez, M. Schlenker and A. Mathiot, Physica 86-88B (1977) 1327.
Magnetic domains and crystal defects were investigated in a crystal of GaxY3Fes_~O]2. Strong interaction was observed between dissolution striations and the magnetization, leading to a characteristic domain configuration involving long range stress creating domain walls pinned to the striations.
The low saturation magnetization of galliumsubstituted yttrium iron garnet, (Ga) YIG, makes it a valuable material for microwave applications. The present study was undertaken in an effort to elucidate the origin of parasitic resonance modes sometimes encountered in spheres of GaxFes_xY3Ol2, with x ~ 1, impairing the device performance. The crystals were grown in closed crucibles in a PbO-PbF2-B203 flux slowly cooled from 1270 to 1000°C. Flux-grown crystals usually feature growth striations, delineating the natural faces at various stages of growth; their orientation is normal to the growth direction and remains constant within the volume (growth sector) generated by a single natural face. The results discussed in the present paper were obtained using a 100 ~m thick plate parallel to (011), hence containing four easy magnetization directions and mainly consisting of a growth sector where the growth direction, [211], was also parallel to the specimen surface. The sample was mechanically polished, but chemical etching in hot phosphoric acid proved necessary in addition in order to obtain X-ray topographs revealing crystal defects and simple ferrimagnetic domain structures [1]; the surface scratches which then became visible in optical examinations are completely invisible on X-ray topographs, and therefore seem to create no strain. Fig. 1 shows the magnetic domain pattern observed with the Faraday effect using slightly tilted illumination. Simple 180 ° domains with in-plane magnetization in the top region exhibit closure domains reminiscent of the edge of a crystal; the lower half of the picture reveals an alternation of bands nor*Also: Institut Laue-Langevin, 156 X, 38042 Grenoble-C~dex, France. **LETI, CENG, 85 X, 38041 Grenoble-C~dex, France.
1322
mal to the growth direction, changing direction at a growth sector boundary (fig. 2b), obviously involving out-of-plane magnetization directions, and of domains with magnetization in the surface and parallel to these bands. Such strong-contrast bands were found to reproduce consistently at the very same locations after being destroyed by a magnetic field. Close examinations in non-polarized light (fig. 2a) as well as X-ray transmission topographs (fig. 2c) indicate, at these locations, the presence of striations. The characteristic curved shape they take at the growth sector boundary (fig. 2a) makes it possible to identify them as dissolution striations [2-4] produced during the growth of the crystal by a temporary
Fig. 1. Magnetic domain pattern of the (011) plate.
Journal of Magnetism and Magnetic Materials 15 - ! 8 (1980) 1322-1324 ©North Holland
C. Mazur~-Espejo et al./ Domains and crystal defects in flux grown GaYIG
1323
C Fig, 2. (a) Dissolution striations observed in nonpolarized light and Co) the corresponding domain bands changing direction at the growth sector boundary. X-ray transmission topographs of the same region: (c) 088 reflection; (d) 444 reflection.
regression of growth followed by a fast catchingup, due to a large temperature fluctuation. It is to be noted that only some of the optically visible striations are decorated with out-of-plane domain bands; on X-ray topographs made in a magnetic field in order to eliminate domain-wall contrast and using a (444) reflection, on which ordinary growth striations in the [211] sector are practically invisible, they retain a rather strong contrast (fig. 2d), indicating they are associated with more complicated lattice distortions. Close observation of the strong-contrast domain bands using the Faraday effect leads, for the simpler type with noncorrugated walls, to the pattern of magnetization distribution shown in fig. 3,
giving a cross section parallel to a (117) plane. It may be noted that, at least in this schematic model, this domain structure is stray-field-free, but involves several walls that give rise to long-range stresses [5, 6]: this domain structure would therefore be unstable in a perfect crystal, and the central, stress-creating (211) wall is probably pinned to the striation largely through interactions with its strain field. A similar situation was encountered earlier in terbium iron garnet [7], although there the resulting domain structure involved stray-fields and was observed only in a magnetic field. In the present case, a dissolution striation forces the magnetization direction to be parallel to it
1324
C. Mazur~-Espejo et al./ Domains and crystal defects in flux grown GaY1G
011
@2)
/'
"~1~
2~1) y"',,,, ®
/
\
_
.
111 =
)
~ ~ 1 1 ~
o~v / I X
/ [11iF
[/'~I~\
/
/// ® ~211
Q . , ,400Hn~ Fig. 4. Reference directions and scale.
Fig. 3. Pattern of magnetization distribution for the simpler domain bands; (111) section.
outside the band-domains shown in fig. 3, thus causing the occurrence of closure domains at some distance as is seen in fig. 1. It therefore has, at least in the statical behaviour of the particularly simple geometry we have investigated, a very strong effect, comparable to that of a free surface. For reference directions and scale see fig. 4. The authors are happy to thank A. Mathiot and R. de Tournemine for their friendly cooperation, and F. Lefaucheux and M. C. Robert for an illuminating discussion.
References
[1] J. Basterfield, J. Appl. Phys. 39 (1968) 5521. [2] J. P. M. Damen and J. M. Robertson, J. Crystal Growth 16 (1972) 50. [3] R. Hergt, M. Wendt, P. Gornert and S. Bormann, Phys. Star. Sol. (a) 35 (1976) 347, [4] S. Gits-L~on, M. C. Robert and A. Zarka, Bull. Mineral 101 (1978) 399. [5] G. Rieder, Abb. Braunschw. Wiss. Ges. 11 (1959) 20. [6] M. Klernan and M. Schlenker, J. Appl. Phys. 43 (1972) 3184. [7] J. Linares-Galvez, M. Schlenker and A. Mathiot, Physica 86-88B (1977) 1327.