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On the Faraday rotation in FeSiO2 granular films
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On the Faradayrotationin Fe-SKI, granularfil Z .S. 3iang a9b,J.T. Ji avb,G.J. Jin gb, H. Sang a*b,G. Guo %b,S.Y. Zhang ‘, Y.W. Du 3r* a N&no1
Laboratoy of Solid State Microstructures, Nanjbg Uniuersity, Nanjing 210008, China b Department of Physics, Nanjing University, Nanjing 210lU8, China
Large Faraday rotation f105 dcg/cm) in Fe-SD, granular films made by ion-beam sputtering method has at room temperature. Our results show that Faraday rotation (FRl increases with Fe volume fraction f, f, = 0.55. This indicates that Fe granules play an important role in FR of granular materials.
Recently there is an increasing interest in the study of magnetic granular systems, from both the theoretical and experimental point of view. Many interesting phenomena, such as giant magnetoresistance in Co-Cu granular fdms [l] and greatly enhanced coercivity in Fe-SiO, granular solids [2] etc., have been observed On the other hand, an important area dealing with magnetooptical effect (MOE) in granular systems remains largely unexplored, despite the fact that MOE is the basis of numerous recording devices. Magnetooptic recording is feasible with non-metals and with metals. ‘The former materials have tt.: advantage of a small optical absorption, but metallic systems generally have larger MOE. In this paper, we report the study of Faraday rotation (FR) in Fe-SiO, granular films where the Fe granules are dispersed in a matrix of amorphous SiO,. This material is more transparent than pure metals near its percolation threshold f, which is about OS-O.6 [3]. Our results show that samples with higher iron concentration exhibit large FR over a wide range of frequencies. The correlation between the FR and microstructures of these films wi!l ako be discussed. All samples were prepared by ion-beam sputtering method onto glass substrates which were fixed at temperature T, = 1OOT. The sputtering targets were mosaic targets of pure iron and SiO, with appropriate arrangements. ‘Ihe Fe volume fractions f, of the samples, between 0.1 and 1.0, were determined using electron microprobe+ The thickness of the films was controlled by deposition time and was adjusted so that the samples were transparent enough for magnetooptical studies. The thickness measure-
* Corresponding author. Fax: + 86-25-3300535.
ment is of vital importance in the studies, and it was with the FPI-IA-STEP 200 analyzer to an about f5 A. The microstructures of the analyzed by ‘IEM and FMR. The microstructures of the Fe-SiO, granular composition dependent. It is similar to t Refs. [2,4]. The FMR spectra show that the for the perpendicular configuration decreases with decreasing f,, this indicates that the structure of the films clr as f, decreases, and the demagn&ing factor of drops accordingly. This can also be seen in ‘I’EM graphs. Fig. la is a TEM micrograph of a typ centration microstructure for a film with f, = 0.24 below f,. Small, roughly spherical and generally isolated Fe particles separated by SiOz matrix are characteristics of these low Fe content samples. As the Fe bontent crosses the percolation threskld, small partic It is obvious in Fig. lb for f,
ones.
0304-88S3/9S/$O9.50 6 1995 Ekevier Science B.V. All rights reserved SSDfO304-8853(94)01241-S
---1 H-19kCk
0
10
40
00
IW
f,G
Fig. 3. Tbe dependence of Faraday rotation on Fe volume frac-
tionsf”.
dar films prepared at
me of FR orI the Fe eagtb A = 770 nm. As
y, MOEarises from the scatterercan be either single
properttesof thesefilms meti
ones, ad FR of the
fihns approaches the value of sputteredpure iron film. Betweenthesetwo regions,one observesa peak of FR at f, = 0.55 near L. In the region of f, =j$ somewell-defined isolated magneticparticlesare stiil present,but the small particles tend to aggregateinto chains with large aspectratio. The shapeof particlesbegins to affect the magnitudeof the rotation as pointed out by Xia et al. [5]. Thus, the enhancementof FR in this region may be attribr’ed to the effect of density and shape of the rnagnetic particles. In conclusion, our experimental study suggeststhat large F’Ris not unique to magnetichomogeneousmedia, but also exists in the magneticinhomogeneoussystems. Large FR is readily observedin Fe-$30, granular films which hasthe order of magnitudeaslarge as 10’ deg/cm. FR in the films is compositiondependentand has a peak near the percolation threshold. From the application point of view, this material is more transparentthan pure metals, therefore,it hasa low optical absorption. Achowkdgemen?: This work is supportedby Grant 85-6 NM, Grant NSFS & NAMCC, SKLM, and Grant 93402 JSNSF.
References [l] J.Q. Xiao, J.S. Jiang and CL. Chien, Phys. Rev. Lett. 68 (1992) 3749. [Z] Gang Xiao and C.L. Cbien, J. Appl. Phys. 63 (198814252. [3] B. Abetes, in: Applied Solid State Science: Advances in Materials and Device Research, ed. H. Wolf (Academic, New York, 1976) p.1. (41 R.L. Holtz, P. Lubitz and A.S. Edelstein, Appl. Phys. Lett. 56 (1990) 943. 151 TX. Xia, P.M. Hui and D. Stroud, J. Appl. Phys. 67 (1990) 2?-16.
On the Faradayrotationin Fe-SKI, granularfil Z .S. 3iang a9b,J.T. Ji avb,G.J. Jin gb, H. Sang a*b,G. Guo %b,S.Y. Zhang ‘, Y.W. Du 3r* a N&no1
Laboratoy of Solid State Microstructures, Nanjbg Uniuersity, Nanjing 210008, China b Department of Physics, Nanjing University, Nanjing 210lU8, China
Large Faraday rotation f105 dcg/cm) in Fe-SD, granular films made by ion-beam sputtering method has at room temperature. Our results show that Faraday rotation (FRl increases with Fe volume fraction f, f, = 0.55. This indicates that Fe granules play an important role in FR of granular materials.
Recently there is an increasing interest in the study of magnetic granular systems, from both the theoretical and experimental point of view. Many interesting phenomena, such as giant magnetoresistance in Co-Cu granular fdms [l] and greatly enhanced coercivity in Fe-SiO, granular solids [2] etc., have been observed On the other hand, an important area dealing with magnetooptical effect (MOE) in granular systems remains largely unexplored, despite the fact that MOE is the basis of numerous recording devices. Magnetooptic recording is feasible with non-metals and with metals. ‘The former materials have tt.: advantage of a small optical absorption, but metallic systems generally have larger MOE. In this paper, we report the study of Faraday rotation (FR) in Fe-SiO, granular films where the Fe granules are dispersed in a matrix of amorphous SiO,. This material is more transparent than pure metals near its percolation threshold f, which is about OS-O.6 [3]. Our results show that samples with higher iron concentration exhibit large FR over a wide range of frequencies. The correlation between the FR and microstructures of these films wi!l ako be discussed. All samples were prepared by ion-beam sputtering method onto glass substrates which were fixed at temperature T, = 1OOT. The sputtering targets were mosaic targets of pure iron and SiO, with appropriate arrangements. ‘Ihe Fe volume fractions f, of the samples, between 0.1 and 1.0, were determined using electron microprobe+ The thickness of the films was controlled by deposition time and was adjusted so that the samples were transparent enough for magnetooptical studies. The thickness measure-
* Corresponding author. Fax: + 86-25-3300535.
ment is of vital importance in the studies, and it was with the FPI-IA-STEP 200 analyzer to an about f5 A. The microstructures of the analyzed by ‘IEM and FMR. The microstructures of the Fe-SiO, granular composition dependent. It is similar to t Refs. [2,4]. The FMR spectra show that the for the perpendicular configuration decreases with decreasing f,, this indicates that the structure of the films clr as f, decreases, and the demagn&ing factor of drops accordingly. This can also be seen in ‘I’EM graphs. Fig. la is a TEM micrograph of a typ centration microstructure for a film with f, = 0.24 below f,. Small, roughly spherical and generally isolated Fe particles separated by SiOz matrix are characteristics of these low Fe content samples. As the Fe bontent crosses the percolation threskld, small partic It is obvious in Fig. lb for f,
ones.
0304-88S3/9S/$O9.50 6 1995 Ekevier Science B.V. All rights reserved SSDfO304-8853(94)01241-S
---1 H-19kCk
0
10
40
00
IW
f,G
Fig. 3. Tbe dependence of Faraday rotation on Fe volume frac-
tionsf”.
dar films prepared at
me of FR orI the Fe eagtb A = 770 nm. As
y, MOEarises from the scatterercan be either single
properttesof thesefilms meti
ones, ad FR of the
fihns approaches the value of sputteredpure iron film. Betweenthesetwo regions,one observesa peak of FR at f, = 0.55 near L. In the region of f, =j$ somewell-defined isolated magneticparticlesare stiil present,but the small particles tend to aggregateinto chains with large aspectratio. The shapeof particlesbegins to affect the magnitudeof the rotation as pointed out by Xia et al. [5]. Thus, the enhancementof FR in this region may be attribr’ed to the effect of density and shape of the rnagnetic particles. In conclusion, our experimental study suggeststhat large F’Ris not unique to magnetichomogeneousmedia, but also exists in the magneticinhomogeneoussystems. Large FR is readily observedin Fe-$30, granular films which hasthe order of magnitudeaslarge as 10’ deg/cm. FR in the films is compositiondependentand has a peak near the percolation threshold. From the application point of view, this material is more transparentthan pure metals, therefore,it hasa low optical absorption. Achowkdgemen?: This work is supportedby Grant 85-6 NM, Grant NSFS & NAMCC, SKLM, and Grant 93402 JSNSF.
References [l] J.Q. Xiao, J.S. Jiang and CL. Chien, Phys. Rev. Lett. 68 (1992) 3749. [Z] Gang Xiao and C.L. Cbien, J. Appl. Phys. 63 (198814252. [3] B. Abetes, in: Applied Solid State Science: Advances in Materials and Device Research, ed. H. Wolf (Academic, New York, 1976) p.1. (41 R.L. Holtz, P. Lubitz and A.S. Edelstein, Appl. Phys. Lett. 56 (1990) 943. 151 TX. Xia, P.M. Hui and D. Stroud, J. Appl. Phys. 67 (1990) 2?-16.