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Magneto-optical effects in Th-substituted yttrium iron garnets
Journal of Magnetism and Magnetic Materials 104-107 (1992) 445-446 North-Holland
Magneto-optical effects in Th-substituted yttrium iron garnets K. Tamanoi, T. Nomoto, T. Anezaki, T. Kuboyama, K. Shinagawa, T. Saito and T. Tsushima Department of Physics, Toho Unicersity, Funabashi City 274, Japan To investigate the effects of Fe 2+ in YIG on the magneto-optical effects, we grow (YTh)3FesOI2 films using an LPE method, and measure the absorption coefficient and the Faraday rotation (FR). A decrease of FR is observed at around the wavelength of 0.52 Ixm. In order to make clear the origin, we calculate the electronic states of a divalent iron-oxygen octahedral cluster using the SCF-Xc~ method. The observed spectra are assigned to the internal transition of an electron from 3d-like eg* orbit to 4p-like tlu one in Fe 2+ on the octahedral site in YIG. It is well known that pure Y I G has a small absorption coefficient (AC) and a large Faraday rotation (FR) in the visible wavelength region, w h e r e the valence of iron ions are trivalent. As Y I G is d o p e d with tetravalent ions such as Ge, Si and others, Fe 2+ ions are p r o d u c e d to c o m p e n s a t e the charge. T h e effect of the Fe 2+ on F R and A C was investigated by Egashira et al. [1] and Dillon et al. [2] in such s u b s t i t u t e d YIG. They found that F R decreases a n d A C increases in comparison with p u r e Y I G in the visible region. However, it is difficult to observe the optical effects by sole Fe 2+ ions, since the m a g n e t i c properties in these materials are affected with such substitutions. Therefore, we grew ( y 3 + , Th4+)3 (Fe3+, Fe2+)5012 films w h e r e y 3 + is s u b s t i t u t e d with Th 4+ without the decrease of the iron content, and F R and A C of these films were measured. As a result, F R decreases at a r o u n d 0.52 Ixm, a n d A C increases with increasing T h c o n t e n t in the whole visible region. F u r t h e r m o r e , to m a k e clear these p h e n o m e n a , we calculate the electronic states of
the (Y, Th)3FesO12 using the unrestricted S C F - X ~ SW m e t h o d based on the divalent i r o n - o x y g e n octahedral cluster model. Single crystalline films of the composition (Y, Th)3Fe5012 were grown by an L P E m e t h o d using P b O - B 2 0 3 as the flux onto (111) o r i e n t e d gadolinium gallium g a r n e t ( G G G ) substrates. Table 1 shows the melt compositions a n d the growth conditions. Table 2 shows the compositions and the thicknesses of the films. T h e compositions of the films were analyzed by an inductively coupled plasma spectroscopy (ICPS). T h e film thickness was d e t e r m i n e d from the m e a s u r e d optical i n t e r f e r e n c e s p e c t r u m using the average refractive index of 2.15. T h e F R was m e a s u r e d in the region of 0.5-0.9 Ixm in the magnetic field of 4.5 kOe at room t e m p e r a t u r e and at 120 K. A C was m e a s u r e d at room t e m p e r a t u r e . T h e m a x i m u m value of T h sustitution in the films was 0.15 (at/f.u.). But it was possible to observe the effect of sole Fe 2+ ions, because the Pb c o n t e n t as the impurity was less than 0.03 (at./f.u.).
Table 1 Melt composition, growth temperature (Tg) and dipping time (D.T.) Melt
Composition mol% Y203
YIG A B C
0.57 0.63 0.51 0.25
ThO 2
Fe203
PbO
B203
Tg [°C]
0.06 0.13 0.25
10.23 10.66 10.66 10.68
84.51 78.80 78.85 78.95
4.69 9.85 9.85 9.87
990 880 850 750
D.T. [min] 3 6 6 12
"Fable 2 Film composition and film thickness (d) Sample
YIG A B C
Composition at/f.u. Y
Th
Pb
Fe
Pt
d [~m]
3.00 2.94 2.90 2.82
0.04 0.09 0.15
0.02 0.0l 0.03
5.00 4.98 5.00 4.99
0.02 0.00 0.01
3.01 4.72 1.69 1.04
0312-8853/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
446
K. Tamanoi et al. / Th-substituted yttrium iron garnets
4000
,
o
Up-Spin
,
....
YIG
Sample A
^
o~ m 3000 "/ / \ \ -- -- . - - Sample B "~ / ~ . . . . Sample C
Down-Spin
0.0
R .T.
eg* (3d) t~ (4p)
(n
m -0.1 0
< I0
~ \ \
2000
®
..Q "10
k\ 1000
\
>-
Q
-0.2
~'-~.._
•\ K j , ' ~ . ~ ,.~-" ~---.¢~ ,../ ..
0
>o 0c ,,,
.~. ....
¢v-100(?
0.5
0.6'
017
018
WAVELENGTH
0.9
(p.rn)
Fig. ]. Faraday rotation spectra in YIG and (YTh)3FesOi2 measured at room temperature.
Figs. 1 and 2 show the F R spectra of ( Y T h ) 3 F e s O l 2 and Y I G at room t e m p e r a t u r e and at 120 K, respectively. It was found that F R at a r o u n d 0.52 ~xm decreases with the increase of T h c o n t e n t in the films in comparison with pure YIG. As the t e m p e r a t u r e was lowered, the tendency becomes more clear as shown in fig. 2. C o r r e s p o n d i n g to the change of FR, it was found that A C increases with the increase of the Th c o n t e n t in the films in the visible region. Especially, at the wavelength of 0.50 ixm, these tendencies are e m i n e n t . To investigate the origin of FR, the electronic states of Fe 2+ in Y I G calculated using the unrestricted SCFX ~ SW m e t h o d on a ( F e 2 + O ~ ) ] 0 - cluster model. T h e exchange p a r a m e t e r s of Fe 2+ and 0 2+ were ass u m e d to be 0.71151 and 0.74447, respectively, and those of the interatomic a n d the extracluster regions were assumed to be 0.73703. T h e F e - O distance was assumed to be 3.815 a.u. (1.0 a . u . = 0.529167 A) [3] 4000
:
l
"
~"'~ 2ooo3°°° f,'1ooo,,,,,,....,;,, 120K o~" ~~°' I--
O
|,J
~
/
-2000 ,<
113
<~ - 3 0 0 0 ~
/
-4ooo i.
.... i
~
Sample i
WAVELENGTH
C
4 i
/
(#m)
Fig. 2. Faraday rotation spectra in YIG and (YTh)3FesOiz measured at 120 K.
-0.3
/ tlg ,* ~, ;
Z uJ
t~t
_I
t2u T ? T
<
-0.4
I--
eft ew
o
a~ (4s) ~-- t2g*(3d)
-7 ~
- - tlg ~t~
~~--~J~J~ ~ t 2 u
tt
t2;; ;.* h. f t t a~g t
/
eg
a~g ~
//-PP-t~t2g
-0.5
-0.6
t2g 4
eg
~
' ~
'
Fig. 3. One electron energy levels of a (Fe 2~ Of )1(I cluster in ground state, and the allowed transitions (vertical arrows). equal to the average F e - O distancc in the F e - O o c t a h e d r o n in YIG. T h e o u t e r s p h e r e radii and the atomic sphere ones for Fe 2+ and O ~- were assumed to bc 5.815, 1.815 and 2.000 a.u., repectivcly. F u r t h e r more, for the sake of charge neutrality, + 10 charges were set on the o u t e r sphere. In addition, for simplicity, the orbits except 3s, 3p and 3d of Fe and the orbit ls of O were assumed to be the core orbits. Fig. 3 shows one electron energy levels and electron configuration of the cluster in the g r o u n d state. Each level is labeled in terms of the irreducible r e p r e s e n t a t i o n of the O h symmetry group. Spin-up electrons and spindown electrons were occupied up to the oxygen t~g 2p-like orbit. Five electrons occupy t,* and eg* 3d-like a n t i b o n d i n g spin-up orbits, and the one residual electron occupies spin-up 4s-like orbit a l g instead of spindown 3d-like t2* one. T h e transitions allowed by the symmetry consideration are shown in the vertical arrows in fig. 3. From the calculated transition energy of 2.14 eV, the c h a n g e of F R at a r o u n d 0.52 ~xm was assigned to the internal transition from Fe 3d-like orbit eg* to 4p-like t IL, orbit of Fe 2 ~ on the octahedral site in YIG. F u r t h e r m o r e , the transition from 4s-like a lg orbit to 4p-like t~u one was f o u n d to a p p e a r at a r o u n d 1.(I ixm. This transition may be responsible for the photomagnetic effect observed in Si4+-substituted Y I G [2].
References [ l ] K . Egashira, T. Manabe and H. Katsuraki, J. Appl. Phys. 42 (1971) 4334. [2] J.F. Dillon, Jr., E.M. Gyorgy and J.P. Remeika, J. Appl. Phys. 41 (1970) 1211. [3] M.A. Gilleo, Ferromagnetic Materials, vol. 2, ed. E.P. Wohlfarth (North-Holland, Amsterdam, 1980) p. 21.
Magneto-optical effects in Th-substituted yttrium iron garnets K. Tamanoi, T. Nomoto, T. Anezaki, T. Kuboyama, K. Shinagawa, T. Saito and T. Tsushima Department of Physics, Toho Unicersity, Funabashi City 274, Japan To investigate the effects of Fe 2+ in YIG on the magneto-optical effects, we grow (YTh)3FesOI2 films using an LPE method, and measure the absorption coefficient and the Faraday rotation (FR). A decrease of FR is observed at around the wavelength of 0.52 Ixm. In order to make clear the origin, we calculate the electronic states of a divalent iron-oxygen octahedral cluster using the SCF-Xc~ method. The observed spectra are assigned to the internal transition of an electron from 3d-like eg* orbit to 4p-like tlu one in Fe 2+ on the octahedral site in YIG. It is well known that pure Y I G has a small absorption coefficient (AC) and a large Faraday rotation (FR) in the visible wavelength region, w h e r e the valence of iron ions are trivalent. As Y I G is d o p e d with tetravalent ions such as Ge, Si and others, Fe 2+ ions are p r o d u c e d to c o m p e n s a t e the charge. T h e effect of the Fe 2+ on F R and A C was investigated by Egashira et al. [1] and Dillon et al. [2] in such s u b s t i t u t e d YIG. They found that F R decreases a n d A C increases in comparison with p u r e Y I G in the visible region. However, it is difficult to observe the optical effects by sole Fe 2+ ions, since the m a g n e t i c properties in these materials are affected with such substitutions. Therefore, we grew ( y 3 + , Th4+)3 (Fe3+, Fe2+)5012 films w h e r e y 3 + is s u b s t i t u t e d with Th 4+ without the decrease of the iron content, and F R and A C of these films were measured. As a result, F R decreases at a r o u n d 0.52 Ixm, a n d A C increases with increasing T h c o n t e n t in the whole visible region. F u r t h e r m o r e , to m a k e clear these p h e n o m e n a , we calculate the electronic states of
the (Y, Th)3FesO12 using the unrestricted S C F - X ~ SW m e t h o d based on the divalent i r o n - o x y g e n octahedral cluster model. Single crystalline films of the composition (Y, Th)3Fe5012 were grown by an L P E m e t h o d using P b O - B 2 0 3 as the flux onto (111) o r i e n t e d gadolinium gallium g a r n e t ( G G G ) substrates. Table 1 shows the melt compositions a n d the growth conditions. Table 2 shows the compositions and the thicknesses of the films. T h e compositions of the films were analyzed by an inductively coupled plasma spectroscopy (ICPS). T h e film thickness was d e t e r m i n e d from the m e a s u r e d optical i n t e r f e r e n c e s p e c t r u m using the average refractive index of 2.15. T h e F R was m e a s u r e d in the region of 0.5-0.9 Ixm in the magnetic field of 4.5 kOe at room t e m p e r a t u r e and at 120 K. A C was m e a s u r e d at room t e m p e r a t u r e . T h e m a x i m u m value of T h sustitution in the films was 0.15 (at/f.u.). But it was possible to observe the effect of sole Fe 2+ ions, because the Pb c o n t e n t as the impurity was less than 0.03 (at./f.u.).
Table 1 Melt composition, growth temperature (Tg) and dipping time (D.T.) Melt
Composition mol% Y203
YIG A B C
0.57 0.63 0.51 0.25
ThO 2
Fe203
PbO
B203
Tg [°C]
0.06 0.13 0.25
10.23 10.66 10.66 10.68
84.51 78.80 78.85 78.95
4.69 9.85 9.85 9.87
990 880 850 750
D.T. [min] 3 6 6 12
"Fable 2 Film composition and film thickness (d) Sample
YIG A B C
Composition at/f.u. Y
Th
Pb
Fe
Pt
d [~m]
3.00 2.94 2.90 2.82
0.04 0.09 0.15
0.02 0.0l 0.03
5.00 4.98 5.00 4.99
0.02 0.00 0.01
3.01 4.72 1.69 1.04
0312-8853/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
446
K. Tamanoi et al. / Th-substituted yttrium iron garnets
4000
,
o
Up-Spin
,
....
YIG
Sample A
^
o~ m 3000 "/ / \ \ -- -- . - - Sample B "~ / ~ . . . . Sample C
Down-Spin
0.0
R .T.
eg* (3d) t~ (4p)
(n
m -0.1 0
< I0
~ \ \
2000
®
..Q "10
k\ 1000
\
>-
Q
-0.2
~'-~.._
•\ K j , ' ~ . ~ ,.~-" ~---.¢~ ,../ ..
0
>o 0c ,,,
.~. ....
¢v-100(?
0.5
0.6'
017
018
WAVELENGTH
0.9
(p.rn)
Fig. ]. Faraday rotation spectra in YIG and (YTh)3FesOi2 measured at room temperature.
Figs. 1 and 2 show the F R spectra of ( Y T h ) 3 F e s O l 2 and Y I G at room t e m p e r a t u r e and at 120 K, respectively. It was found that F R at a r o u n d 0.52 ~xm decreases with the increase of T h c o n t e n t in the films in comparison with pure YIG. As the t e m p e r a t u r e was lowered, the tendency becomes more clear as shown in fig. 2. C o r r e s p o n d i n g to the change of FR, it was found that A C increases with the increase of the Th c o n t e n t in the films in the visible region. Especially, at the wavelength of 0.50 ixm, these tendencies are e m i n e n t . To investigate the origin of FR, the electronic states of Fe 2+ in Y I G calculated using the unrestricted SCFX ~ SW m e t h o d on a ( F e 2 + O ~ ) ] 0 - cluster model. T h e exchange p a r a m e t e r s of Fe 2+ and 0 2+ were ass u m e d to be 0.71151 and 0.74447, respectively, and those of the interatomic a n d the extracluster regions were assumed to be 0.73703. T h e F e - O distance was assumed to be 3.815 a.u. (1.0 a . u . = 0.529167 A) [3] 4000
:
l
"
~"'~ 2ooo3°°° f,'1ooo,,,,,,....,;,, 120K o~" ~~°' I--
O
|,J
~
/
-2000 ,<
113
<~ - 3 0 0 0 ~
/
-4ooo i.
.... i
~
Sample i
WAVELENGTH
C
4 i
/
(#m)
Fig. 2. Faraday rotation spectra in YIG and (YTh)3FesOiz measured at 120 K.
-0.3
/ tlg ,* ~, ;
Z uJ
t~t
_I
t2u T ? T
<
-0.4
I--
eft ew
o
a~ (4s) ~-- t2g*(3d)
-7 ~
- - tlg ~t~
~~--~J~J~ ~ t 2 u
tt
t2;; ;.* h. f t t a~g t
/
eg
a~g ~
//-PP-t~t2g
-0.5
-0.6
t2g 4
eg
~
' ~
'
Fig. 3. One electron energy levels of a (Fe 2~ Of )1(I cluster in ground state, and the allowed transitions (vertical arrows). equal to the average F e - O distancc in the F e - O o c t a h e d r o n in YIG. T h e o u t e r s p h e r e radii and the atomic sphere ones for Fe 2+ and O ~- were assumed to bc 5.815, 1.815 and 2.000 a.u., repectivcly. F u r t h e r more, for the sake of charge neutrality, + 10 charges were set on the o u t e r sphere. In addition, for simplicity, the orbits except 3s, 3p and 3d of Fe and the orbit ls of O were assumed to be the core orbits. Fig. 3 shows one electron energy levels and electron configuration of the cluster in the g r o u n d state. Each level is labeled in terms of the irreducible r e p r e s e n t a t i o n of the O h symmetry group. Spin-up electrons and spindown electrons were occupied up to the oxygen t~g 2p-like orbit. Five electrons occupy t,* and eg* 3d-like a n t i b o n d i n g spin-up orbits, and the one residual electron occupies spin-up 4s-like orbit a l g instead of spindown 3d-like t2* one. T h e transitions allowed by the symmetry consideration are shown in the vertical arrows in fig. 3. From the calculated transition energy of 2.14 eV, the c h a n g e of F R at a r o u n d 0.52 ~xm was assigned to the internal transition from Fe 3d-like orbit eg* to 4p-like t IL, orbit of Fe 2 ~ on the octahedral site in YIG. F u r t h e r m o r e , the transition from 4s-like a lg orbit to 4p-like t~u one was f o u n d to a p p e a r at a r o u n d 1.(I ixm. This transition may be responsible for the photomagnetic effect observed in Si4+-substituted Y I G [2].
References [ l ] K . Egashira, T. Manabe and H. Katsuraki, J. Appl. Phys. 42 (1971) 4334. [2] J.F. Dillon, Jr., E.M. Gyorgy and J.P. Remeika, J. Appl. Phys. 41 (1970) 1211. [3] M.A. Gilleo, Ferromagnetic Materials, vol. 2, ed. E.P. Wohlfarth (North-Holland, Amsterdam, 1980) p. 21.