Temperature dependent magnetic properties of the 1.2μm bubble diametercompositions (La,Sm,Lu,Tm)3(Fe,Ga)5O1 2 and (La,Sm,Lu,Tm,Ca)3(Fe,Ge)5O1 2D. M. Gualtieri and P. F. Tumelty Citation: Journal of Applied Physics 55, 2545 (1984); doi: 10.1063/1.333723 View online: http://dx.doi.org/10.1063/1.333723 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/55/6?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Temperaturedependent magnetic properties of (Y,Sm,Lu,Tm,Ca)3(Fe,Ge)5O12 epitaxial garnet films J. Appl. Phys. 50, 7824 (1979); 10.1063/1.326779 Growth and magnetic properties of the (Y, Sm, Lu, Ca)3(Ga, Ge, Fe)5O12 garnet films for bubblememoryapplications J. Appl. Phys. 50, 3588 (1979); 10.1063/1.326305 (YSmLu)3(FeGa)5O12 for 1 to 3 μmdiameter bubble devices J. Appl. Phys. 49, 1873 (1978); 10.1063/1.324843 LuSm)3Fe5−x Ga x O12 garnet films for small bubble diameters AIP Conf. Proc. 29, 105 (1976); 10.1063/1.30537 (EuTm)3(FeGa)5O12 garnet films with onemicron diameter magnetic bubbles AIP Conf. Proc. 24, 582 (1975); 10.1063/1.30180

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

69.166.47.134 On: Wed, 17 Dec 2014 05:48:13

Temperature dependent magnetic properties of the 1.2-,um bubble diameter compositions (La,Sm,Lu,Tmh(Fe,Ga)s012 and (La,Sm,Lu,Tm,Cah(Fe,Ge)s012

D. M. Gualtieri and P. F. Tumelty Allied Corporation, Morristown, New Jersey 07960

Magnetic garnet films of composition (La,Sm,Lu,Tmb(Fe,Ga)S012 and (La,Sm,Lu,Tm,Cab (Fe,Ge)S012 were grown on (111 )-oriented substrates of Gd3GaS012 to meet a typical as-grown room-temperature specification for a device utilizing bubbles of 1.2-,um nominal diameter: 0.90-1.30,um thickness, 1.00-1.4O,um stripe width, 300-350 Oe collapse field, lS00-22oo Oe anisotropy field, Q> 2.S, film/substrate lattice constant mismatch < 0.3 pm, and the magnitude of the temperature coefficient of the bubble collapse field measured at 50 DC between 0.21 % and 0.23% DC-I. Films were grown at about 960 DC from a PbO/Bz0 3 flux using the isothermal dipping technique with rotation. Growth rate was adjusted in the range 0.40-0.95 ,urn min - I to attain a desired characteristic length of 0.130-0.145 ,urn. The role of Tm is to reduce the magnetization at a given Curie temperature, which allows films to be grown at a Curie temperature of 470 K and a magnetization of 6S0 G for the Ga-substituted composition, and a Curie temperature of 493 K and a magnetization of 660 G for the (Ca,Ge)-substituted composition. Film properties were measured over a temperature range of - 20 to + 100 DC by optical and FMR techniques. The temperature coefficient of the anisotropy field is nearly constant from - 20 to + 100 DC and has a value of about - 0.7% DC-I in both compositions.

PACS numbers: 75.70.Kw, 75.50.Gg, S1.15.Lm

INTRODUCTION

Small-bubble garnets must have higher magnetization and larger magnetic anisotropy than their larger bubble counterparts. I Higher magnetization is easily obtained by reducing the substitution of nonmagnetic ions for tetrahe­dral iron in a given composition. Magnetic anistropy, which arises in compositions such as (Y,Sm,Lu,Cab(Fe,Ge)sOI2 from the growth-induced pairing oflarge (Sm) and small (Lu) rare-earth ions on the dodecahedral garnet sites, can be in­creased by increasing the concentrations of these ions. Mag­netic anisotropy is proportional to the product of the Sm and Lu concentrations, Z but Sm damps magnetic bubble move­ment. Lu does not, so that increasing the concentration ofLu while keeping the Sm concentration constant and adding a large, nondamping ion to maintain lattice constant will re­sult in a high anisotropy-high mobility composition.

This line of reasoning led3 to the development at Bell Laboratories of two significant small bubble compositions grown on substrates of (111 )Gd3GasOlz; namely, LIlo.z SIIlo.6 Lul.6 CIlo.6 Fe4.4 GeO.6 0IZ which supports 1.1-,um­diam magnetic bubbles, and LIlo.6SIIlo.3Luz.1 Fe4 .1 GIlo.9012 which supports 1.3-,um-diam magnetic bubbles. Although the room-temperature properties of such compositions are suitable for bubble memory devices, the temperature coeffi­cient of the bubble-collapse field abc is too large to allow device operation over an extended temperature range if con­ventional barium ferrite biasing magnets are used. The Ga­substituted composition in particular would be expected to have a very large value of abc since its Curie temperature T c is low (430 K).

Giess, Kobliska, and Cardone4 investigated similar film compositions grown on (111) Nd3GaS0 12 which had smaller values of the characteristic length parameter I, but Q gener­ally less than 2.5. The high Curie temperatures of their com­positions could potentially give low values of abc at bubble diameters less than 1 ,urn.

Davies, Galli, and SuitsS reduced abc ofthe 3-,um com­position (Y,Sm,Lu,Cab(Fe,Ge)sOI2 by substituting a mag­netic rare earth ion Tm for Lu. Thulium substitution for Y in a similar 1. 75-,um bubble diameter composition was found to reduce abc while maintaining high anisotropy.6 Similarly, Yamaguchi, Uchishiba, and Suzuki7 and Ishida and Tanigu­chiS have substituted Er and Gd into such compositions to reduce abc by large amounts, but often at the expense of linearity of the bubble-collapse field temperature profile. Such substitution of magnetic rare-earth ions reduces the net magnetization of the garnet at a given Curie temperature, so that higher Curie temperature materials can be produced which have the required magnetization to support a given bubble diameter. The net effect of the substitution is to push the steep dM / dT region near Tc to higher temperatures and generally flatten the bubble-collapse field temperature pro­file above room temperature.

The compositions chosen for this study employ Tm substitution for Lu and La in (La,Sm,Lu)s(Fe,Ga)S012 and (La,Sm,Lu,Cab(Fe,Ge)sOI2 to produce films which are suit­able for devices using 1.2-,um-diam magnetic bubbles. Table I lists a specification for such a material. All films were

TABLE I. Specification for a 1.2-f.Lm bubble-diameter material.

Thickness (f.Lm)

Stripe width (f.Lm)

Collapse field (Oe)

Anisotropy field (Oe)

Quality factor

Temperature coefficient of the bubble-collapse field (% °C~ I at 50 0q

Film/substrate lattice constant mismatch (corrected for strain)

0.90<h< 1.30

I.oo<w< 1.40

3OO<Ho<350

18oo<H. <2200

Q>2.8

0.21;;;. labc 1<0.23

l.dal <0.30 pm

2545 J. Appl. Phys. 55 (6),15 March 1984 0021-8979/84/062545-03$02.40 @ 1984 American Institute of Physics 2545

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

69.166.47.134 On: Wed, 17 Dec 2014 05:48:13

TABLE II. Melt compositions used in the growth of the films in Table III.

Melt A B C D

R, = Fe20 3/R2OJ 14 12 15 IS R2 = Fe20 3/Ga,O, IS 14 R2 = 2Fe20 3/GeO, 9.8 10.0 R, = PbO/2B2O , 7.4 5.0 7.4 7.4 R4 = Solute Conc. 0.23 0.24 0.24 0.24 R5 = CaO/IGe02 + CaO) 0.45 0.45 La20 3/R,O, 0.28 0.27 0.10 0.18 Sm2OJ/R,O, 0.17 0.19 0.24 0.22 Lu2O,/R,O, 0.18 0.23 0.56 0.40 Tm2O,/R2O, 0.37 0.31 0.10 0.20

grown on I-in. (2.54 cm) diameter (111) Gd3Gas012 sub­strates using the isothermal dipping technique9 with a unidi­rectional rotation rate of 200 rev min - I.

GALLIUM COMPOSITIONS

Two melt compositions (A and B) for the growth of films of (La,Sm,Lu,Tmb(Fe,Ga)sOI2 appear in Table II. These melts are specified by the parametric convention es­tablished in Ref. 10. La20 3 has a smaller heat of mixing with the flux that the other rare-earth oxides, and as a result the R I parameter is smaller than that for conventional garnet melts. 11

Optimum room temperature properties, as shown in Table III (films AI, A2, Bl, and B2), were obtained at a growth rate of about 0.9 j.tm min - I. Curie temperatures of about 470 K give an exchange constant of about 2.7 X 10-7

erg/ cm. 12 A characteristic length of 0.137 j.tm would allow the best utilization of the permitted values of film thickness at a Q of 3.0. 13

Compositional analysis was done for a film grown from melt "A." Wavelength-dispersive analysis was accom­plished with a JEOL model JXA-50A electron microprobe and ZAF (atomic number, absorption, and fluorescence) ma­trix corrections by a Krisel Corp. automation system. The resulting formula unit, normalized to 20 atoms, was Lao. 14 SmO.60 LUO.S8 Tmu2 Fe4.30 Gao 60 0 1228 , All elements,

340 ..... Q)

o ...... '0 320

Qi u:: Q) 300 CII a. ~ o 280 ()

Q)

• o • o •

o

:0 28 .c °as. ~ 0

-20

o (La,Sm,Lu,Tm),(Fe,Ga).012

• (La,Sm,Lu,Tm,Ca),(Fe,Ge).012 . o e.

Q 0

• 0 • 0

• 0 • 0

• 0 • 0

• 0

• i

20 40 80

Temperature (DC)

o .

80

i 8

e

100

en -.., if <D

:E 1.20 0: -1. 10 ::r ..... 1.00 §

......

FIG. I. Temperature dependence of the bubble-collapse field and stripewidth for films B2 (Ga) and DI (Ca,Ge). These films have an abc of - 0.222% "C-' at 50"C.

including oxygen, were directly measured, and errors up to 5% can be expected for any element.

(CALCIUM, GERMANIUM) COMPOSITIONS

Two melt compositions (C and D) for the growth of films of (La,Sm,Lu,Tm,Cab(Fe,Ge)sOI2 appear in Table II. Optimum room temperature properties, as shown in Table III (films Cl, C2, and Dl), were obtained at growth rates of about 0.65 j.tm min -I (melt "C") and about 0.45 j.tm min - I

(melt "D"). Curie temperatures of about 490 K give an ex­change constant of about 3.1 X 10-7 erg/cm.12 A character­istic length of 0.143 j.tm would allow the best utilization of the permitted values of film thickness at a Q of 3,0. 13

Compositional analysis of a film grown from melt "C" gave as a measured formula unit Lao.os SmO.79 LU U6 Tffio.so Cao.55 Fe4 .57 GeO.48 0 12.50 , All ele­ments, including oxygen, were directly measured, and errors up to 5% can be expected for any element. Note that a smaller La substitution was required for lattice match than

TABLE III. Properties of (La, Sm, Lu, Tmh(Fe, Ga)50'2 and ILa, Sm, Lu, Tm, Cah(Fe, Ge)5012 films.

Film Al A2 BI B2 CI C2 D1

Composition Ga Ga Ga Ga (Ca,Ge) ICa,Ge) ICa,Ge) Growth temperature ("C) 967.5 965.6 960.0 960.2 968.0 967.5 969.5 Growth rate (pm/min) 0.65 0.90 0.90 0.95 0.65 0.68 0.42 Thickness ( pm) 0.93 1.12 1.48 1.02 1.23 1.42 1.07 Stripe width Ipm) 1.11 1.17 1.33 1.18 1.26 1.33 1.22 Curie temperature (K) 468.7 470.7 468.7 469.6 485.6 485.6 493.4 Collapse field (Oe) 315.2 349.0 362.3 326.0 322.8 350.8 323.3 Exchange const. (10- 7 erg/cm) 2.69 2.72 2.69 2.71 2.96 2.96 3.09 411'M,(G) 681 688 650 689 648 645 676 Characteristic length (pm) 0.134 0.132 0.137 0.136 0.141 0.140 0.142 Q(calc) 3.08 3.03 2.92 3.46 2.78 2.75 3.07 Q(FMR) 3.39 3.23 3.31 2.58 Hdcalc,Oe) 2100 2080 1900 2390 1800 1780 2080 Hk(FMR,Oe) 2337 2090 2135 1745 Lattice const. (nm) 1.23861 1.238 15 1.23864 1.23870 1.23902 Temp. coeft'. of collapse field

1% "C-' at 50"C) -0.214 - 0.241 - 0.222 - 0.255 - 0.222

2546 J. Appl. Phys., Vol. 55, No.6, 15 March 1984 D. M. Gualtieri and P. F. Tumelty 2546

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

69.166.47.134 On: Wed, 17 Dec 2014 05:48:13

3000

CD 2500

o -::2 Q)

~ 2000

>. 0. o '--o CI) 1500 c::

<C

1000

(Fe,Ga>SO 12

-20 0 20 40 60 80 100

Temperature (Oe)

FIG. 2. Temperature dependence of the anisotropy field for films B2 (Ga) and DI (Ca,Ge).

in the Ga composition, since the large ion Ca serves to in­crease the lattice constant as well. The affect of larger Tm concentrations on abc is easily seen in the data for films Cl and Dl.

TEMPERATURE-DEPENDENT PROPERTIES

Figure 1 shows the temperature dependence from - 20 to + l00·C of stripe width and bubble-collapse field for Ga­substituted (B2) and (Ca,Gej-substituted (Dl) films of the same temperature coefficient of the bubble-collapse field at 50'C. The (Ca,Ge) film has a more linear bubble-collapse field temperature profile. Figure 2 shows the variation of the anisotropy field Hk over the same temperature range. The anisotropy field Hk was determined by the usual FMR tech­nique. 14 The temperature coefficient of Hk for the (Ca,Ge)

2547 J. Appl. Phys., Vol. 55, No.6, 15 March 1984

composition is about - 0.70% 'C- I, and that for the Ga

composition is about - 0.65% 'C- I, each fairly constant

over the entire temperature range.

SUMMARY

(La,Sm,Lu, Tmh(Fe,Ga)5012 and (La,Sm,Lu, Tm,Cah (Fe,Ge)5012 films have been produced which meet a typical as-grown specification for a 1.2-pm bubble diameter materi­al. These compositions have a similar temperature depen­dence of the anisotropy field (aHK = - 0.7% 'C- I

) and a variation of stripe width of less than 0.2 pm from - 20 to + l00'C. The temperature profile of the bubble collapse

field is significantly more linear in the (Ca,Ge) composition than the Ga composition.

ACKNOWLEDGMENTS

The authors acknowledge the expert technical assis­tance of C. B. Herein and D. D. Badding in the growth and characterization of the films. Compositional analysis was done by J. E. Macur and L. E. Reinhardt. M. A. Gilleo par­ticipated in the development of the Ga compositions.

IA. A. Thiele, Bell Sys. Tech. I. 48, 3287 (1969). 2A. H. Eschenfelder, I. Appl. Phys. 49,1891 (1978). 35. L. Blank, R. Wolfe, L. C. Luther, R. C. LeCraw, T. I. Nelson, and W. A. Biolsi, I. Appl. Phys. 50, 2155 (1979).

4E. A. Giess, R. I. Kobliska, and F. Cardone, I. Appl. Phys. 50, 7818 (1979).

51. E. Davies, G. Galli, and J. C. Suits, J. Appl. Phys. 49, 1859 (1978). 6D. M. Gualtieri, P. F. Tumelty, and M. A. Gilleo, J. Appl. Phys. 50, 7824 (1979).

7K. Yamaguchi, H. Uchishiba, and T. Suzuki, IEEE Trans. Magn. MAG· 16,616(1980).

SF. Ishida and Y. Taniguchi, Mater. Res. Bull. 17, 1483 (1982). 9H. I. Levinstein, S. Licht, R. W. Landorf, and S. L. Blank, Appl. Phys. Lett. 19,486 (1971).

lOS. L. Blank, W. A. Biolsi, and J. W. Nielsen, IEEE Trans. Magn. MAG· 13, 1095 (1977).

liD. M. Gualtieri, I. Appl. Phys. 50, 2170 (1979). 12J. C. Slonczewski, A. P. Malozemoff, and E. A. Giess, Appl. Phys. Lett.

24,396 (1974). 13D. M. Gualtieri, IEEE Trans. Magn. MAG·16, 1440 (1980). 14D. C. Cronemeyer, AlP Conference Proceedings (Magnetism and Magnet­

ic Materials-l 973), edited by C. D. Graham, Jr. and J. I. Rhyne (Ameri­can Institute of Physics, New York, 1974), Vol. 18, pp. 85-89.

D. M. Gualtieri and P. F. Tumelty 2547

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

69.166.47.134 On: Wed, 17 Dec 2014 05:48:13