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Substituted rare earth garnet substrate crystals and LPE films for magnetooptic applications
Journal of Crystal Growth 42 (1977) 343—344 © North-Holland Publishing Company
SUBSTITUTED RARE EARTH GARNET SUBSTRATE CRYSTALS AND LPE FILMS FOR MAGNETOOPTIC APPLICATIONS M. KESTIGIAN, W.R. BEKEBREDE and A.B. SMITH Sperry Research Center, Sudbury, Massachusetts 01776, USA
Novel substituted transparent rare earth garnet substrates with lattice parameters as large as 12.569 A were grown from the direct melt by the Czochralski technique. These single crystals were fabricated, polished and used as substrates in the LPE deposition of magnetic garnet thin films. The use of these large unit cell parameters has resulted in obtaining magnetooptic iron garnet films containing the light (larger radii) rare earths and bismuth. Faraday rotation measurements made on representative samples at 0.6337 ~m showed Faraday rotations as high as —25.2 X l0~deg/cm.
1. Introduction
ted for the gallium in the octahedral site of 3G [3,4]. A unit cell of a0 = 12.50 A was obtained from single crystals grown from a melt with a gallium-to-scandium ratio 4 : 1. When the gallium-to-scandium ratio was adjusted to 3 : 2 in the melt, single crystals with a unit cell parameter of 12.569 A were obtained. Thus, on the concentration scandium that isdepending incorporated within these limits,ofany a 0 between 12.569 and 12.383 A is achievable. Lattice parameters larger than that of 3G were obtained also by the incorporation of calcium in the dodecahedral position with a concomitant incorporation of zirconium to preserve charge neutrality [5]. A garnet unit cell with a0 = 12.478 A was reached conveniently by this approach. This lattice parameter was attamed from a melt which contained a 15% CaZrO3 addition. Single crystals of the above materials were grown from the direct melt by the Czochralski method. The apparatus used in these crystal growth experiments has been described previously [6]. The wafers fabricated from these crystals were colorless and transparent. Samarium gallium garnet single crystals with a lattice parameter of 12.432 A were also grown for use as substrates, but the use of SmGaG was restricted because it has absorption bands in the visible region. A summary of nonmagnetic garnets used as substrate materials is given in table 1. Uquid-phase epitaxial depositions were carried out using polished (11 1)-oriented substrate slices. The
Rare earth iron garnets have been used in several magnetooptic devices [1]. These devices have been largely restricted to operation in the 1 to 5 pm wavelength region because it is at these wavelengths that the absorption coefficient is low thedescribes ratio of 0F to a is ahigh. Thisand paper Faraday rotation the preparation and evaluation of substituted rare earth garnet LPE films which have improved Faraday rotation in the visible wavelength region.
2. Single crystal growth and liquid phase epitaxy Commercially available gadolinium gallium garnet (3G) substrate wafers can be used for the deposition of magnetic garnet films whose lattice parameters are matched to that of 3G. However, the incorporation of larger ionic radii rare earth cations and increased concentrations of bismuth in the magnetic garnet thin films, together with the desirability of maintaining approximate film—substrate lattice match, demand formulation and preparation of nonmagnetic garnet substrates with lattice parameters greater than that of 3G (12.383 A) [2]. We report here the growth of bismuth-containing garnet thin films on such substrates. In our experiments, the increased lattice constant was achieved by means of several different modiuications to 3G. In one approach, scandium was substitu343
344
M. Kestigian et al.
/ Substituted rare earth garnet substrate crystals
Table
1 Substrate materials for LPE deposition of magnetooptic thin films a
0(A)
Gadolinium gallium garnet (3G) 3G + 5% CaZrO3 a 3G + 10% CaZrO3 a 3G + 15% CaZrO3 a Gd3Sc1Ga4O12 a Gd3Sc2Ga3O12 a
Sm3Ga5O12
3. Property measurements Film thickness was obtained by interferometric methods. Lattice match-mismatch between substrate and film was measured by X-ray diffraction. Faraday rotation experiments were performed at 0.6337 pm. Representative results are presented in table 3. The Faraday rotation for YIG is included in this table for
12.383 12.404 12.436 12.478 12.500 12.569 12.432
comparison. It can be observed readily that the compositions which contain the larger rare earth cations, together with bismuth, exhibit the highest Faraday rotation values.
a Melt composition
Table 2 LPE melt
Acknowledgements composition used to prepare (PrGdBi)3Fe5O12 Mole %
__________________________________________________ Gd203 0.50 Pr203 0.22 Fe203 10.59 Bi203 26.41 PbO 54.68 B203 7.60
The authors wish to thank F.A. Bradlee for assistance with substrate fabrication, F.G. Garabedian for single crystal growth and LPE experiments and W. Goller for magnetic evaluation measurements. References Scott and (1976) 292.
[1] G.B.
fabrication and polishing procedures employed were very similar to those used to prepare substrates for the deposition of bubble memory thin films and have been described previously [7]. The LPE magnetic thin films were grown at constant temperature from a supersaturated solution. The film growth temperature was 10 to 200 below the saturation temperature. A typical bismuth LPE melt composition is given in table 2. Gd3Sc2Ga3O12 substrates were used and lattice-matched films resulted.
D.E. Lacklison, IEEE Trans. MAG-12
[2] J.M. Robertson, P.K. Larsen and P.F. Bongers, IEEE Trans. MAG-il (1975) 1112. [3] C.D. Brandle and R.L. Barns, J. Crystal Growth 20 (1973) 1. [4] K. Chow, G.A. Keig and A.M. Hawley, J. Crystal Growth 23 (1974) 58. [5] D. Mateika, J. Herrnring, R. Rath and Ch. Rusche, J. Crystal Growth 30(1975)311. [6] F.G. Garabedian, M. Kestigian, P.C. von Thuna and M.L. Cohen, Am. Ceram. Soc. Bull. 55 (1976) 726. [7] M. Kestigian and W.R. Bekebrede, presented at the Third Am. Conf. on Crystal Growth, Stanford, California, 1975.
Table 3 Faraday rotation at 0.6337 ~m for various magnetooptic LPE films Film composition
(GdBi)3(GaFe)5012 (LuBi)3Fe5O12 (YbPrBi)3Fe5O12 (GdPrBi)3(GaFe)5012 Y3Fe5O12
Substrate
3G+ 15%CaZrO3 3G 3G+ l5%CaZrO3 Gd3Sc2Ga3O12 3G
Film unit cell parameter (A) 12.478 12.361 12.440 12.558 12.376
(deg/cm X 10~) —3.75 —8.8 9.9 —25.2 +1.25
SUBSTITUTED RARE EARTH GARNET SUBSTRATE CRYSTALS AND LPE FILMS FOR MAGNETOOPTIC APPLICATIONS M. KESTIGIAN, W.R. BEKEBREDE and A.B. SMITH Sperry Research Center, Sudbury, Massachusetts 01776, USA
Novel substituted transparent rare earth garnet substrates with lattice parameters as large as 12.569 A were grown from the direct melt by the Czochralski technique. These single crystals were fabricated, polished and used as substrates in the LPE deposition of magnetic garnet thin films. The use of these large unit cell parameters has resulted in obtaining magnetooptic iron garnet films containing the light (larger radii) rare earths and bismuth. Faraday rotation measurements made on representative samples at 0.6337 ~m showed Faraday rotations as high as —25.2 X l0~deg/cm.
1. Introduction
ted for the gallium in the octahedral site of 3G [3,4]. A unit cell of a0 = 12.50 A was obtained from single crystals grown from a melt with a gallium-to-scandium ratio 4 : 1. When the gallium-to-scandium ratio was adjusted to 3 : 2 in the melt, single crystals with a unit cell parameter of 12.569 A were obtained. Thus, on the concentration scandium that isdepending incorporated within these limits,ofany a 0 between 12.569 and 12.383 A is achievable. Lattice parameters larger than that of 3G were obtained also by the incorporation of calcium in the dodecahedral position with a concomitant incorporation of zirconium to preserve charge neutrality [5]. A garnet unit cell with a0 = 12.478 A was reached conveniently by this approach. This lattice parameter was attamed from a melt which contained a 15% CaZrO3 addition. Single crystals of the above materials were grown from the direct melt by the Czochralski method. The apparatus used in these crystal growth experiments has been described previously [6]. The wafers fabricated from these crystals were colorless and transparent. Samarium gallium garnet single crystals with a lattice parameter of 12.432 A were also grown for use as substrates, but the use of SmGaG was restricted because it has absorption bands in the visible region. A summary of nonmagnetic garnets used as substrate materials is given in table 1. Uquid-phase epitaxial depositions were carried out using polished (11 1)-oriented substrate slices. The
Rare earth iron garnets have been used in several magnetooptic devices [1]. These devices have been largely restricted to operation in the 1 to 5 pm wavelength region because it is at these wavelengths that the absorption coefficient is low thedescribes ratio of 0F to a is ahigh. Thisand paper Faraday rotation the preparation and evaluation of substituted rare earth garnet LPE films which have improved Faraday rotation in the visible wavelength region.
2. Single crystal growth and liquid phase epitaxy Commercially available gadolinium gallium garnet (3G) substrate wafers can be used for the deposition of magnetic garnet films whose lattice parameters are matched to that of 3G. However, the incorporation of larger ionic radii rare earth cations and increased concentrations of bismuth in the magnetic garnet thin films, together with the desirability of maintaining approximate film—substrate lattice match, demand formulation and preparation of nonmagnetic garnet substrates with lattice parameters greater than that of 3G (12.383 A) [2]. We report here the growth of bismuth-containing garnet thin films on such substrates. In our experiments, the increased lattice constant was achieved by means of several different modiuications to 3G. In one approach, scandium was substitu343
344
M. Kestigian et al.
/ Substituted rare earth garnet substrate crystals
Table
1 Substrate materials for LPE deposition of magnetooptic thin films a
0(A)
Gadolinium gallium garnet (3G) 3G + 5% CaZrO3 a 3G + 10% CaZrO3 a 3G + 15% CaZrO3 a Gd3Sc1Ga4O12 a Gd3Sc2Ga3O12 a
Sm3Ga5O12
3. Property measurements Film thickness was obtained by interferometric methods. Lattice match-mismatch between substrate and film was measured by X-ray diffraction. Faraday rotation experiments were performed at 0.6337 pm. Representative results are presented in table 3. The Faraday rotation for YIG is included in this table for
12.383 12.404 12.436 12.478 12.500 12.569 12.432
comparison. It can be observed readily that the compositions which contain the larger rare earth cations, together with bismuth, exhibit the highest Faraday rotation values.
a Melt composition
Table 2 LPE melt
Acknowledgements composition used to prepare (PrGdBi)3Fe5O12 Mole %
__________________________________________________ Gd203 0.50 Pr203 0.22 Fe203 10.59 Bi203 26.41 PbO 54.68 B203 7.60
The authors wish to thank F.A. Bradlee for assistance with substrate fabrication, F.G. Garabedian for single crystal growth and LPE experiments and W. Goller for magnetic evaluation measurements. References Scott and (1976) 292.
[1] G.B.
fabrication and polishing procedures employed were very similar to those used to prepare substrates for the deposition of bubble memory thin films and have been described previously [7]. The LPE magnetic thin films were grown at constant temperature from a supersaturated solution. The film growth temperature was 10 to 200 below the saturation temperature. A typical bismuth LPE melt composition is given in table 2. Gd3Sc2Ga3O12 substrates were used and lattice-matched films resulted.
D.E. Lacklison, IEEE Trans. MAG-12
[2] J.M. Robertson, P.K. Larsen and P.F. Bongers, IEEE Trans. MAG-il (1975) 1112. [3] C.D. Brandle and R.L. Barns, J. Crystal Growth 20 (1973) 1. [4] K. Chow, G.A. Keig and A.M. Hawley, J. Crystal Growth 23 (1974) 58. [5] D. Mateika, J. Herrnring, R. Rath and Ch. Rusche, J. Crystal Growth 30(1975)311. [6] F.G. Garabedian, M. Kestigian, P.C. von Thuna and M.L. Cohen, Am. Ceram. Soc. Bull. 55 (1976) 726. [7] M. Kestigian and W.R. Bekebrede, presented at the Third Am. Conf. on Crystal Growth, Stanford, California, 1975.
Table 3 Faraday rotation at 0.6337 ~m for various magnetooptic LPE films Film composition
(GdBi)3(GaFe)5012 (LuBi)3Fe5O12 (YbPrBi)3Fe5O12 (GdPrBi)3(GaFe)5012 Y3Fe5O12
Substrate
3G+ 15%CaZrO3 3G 3G+ l5%CaZrO3 Gd3Sc2Ga3O12 3G
Film unit cell parameter (A) 12.478 12.361 12.440 12.558 12.376
(deg/cm X 10~) —3.75 —8.8 9.9 —25.2 +1.25