HAL Id: jpa-00227276
https://hal.archives-ouvertes.fr/jpa-00227276
Submitted on 1 Jan 1987
HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
4f STATE WITH THE 3d CORE HOLE OF La, Sm AND SmB6
K. Tsutsumi, O. Aita, K. Ichikawa
To cite this version:
K. Tsutsumi, O. Aita, K. Ichikawa. 4f STATE WITH THE 3d CORE HOLE OF La, Sm AND SmB6.
Journal de Physique Colloques, 1987, 48 (C9), pp.C9-915-C9-918. �10.1051/jphyscol:19879162�. �jpa-
00227276�
JOURNAL DE PHYSIQUE
Colloque C9, suppl6ment au n012, Tome 48, dgcembre 1987
4 f STATE WITH THE 3d CORE HOLE OF La, Sm AND SmB,
K. TSUTSUMI, 0. AITA and K. ICHIKAWA
College o f Engineering. University o f Osaka Prefecture, MOzu, Sakai , Osaka 591, Japan
Abstract
-The Sm M4.5 emission and characteristic isochromat spectra of Sm metal and a mixed-valence compound SmB6 and the La M4,5 fluorescent emission spectrum of La metal were measured to obtain the information on the 4f state with the 3d core hole. In the case of Sm metal and SmB6 it was found that an electron-beam energy larger than the energy of the resonant emission (1079 eV) and also the threshold of the 3d5/2 leyel (1082.2 eV is required for the A
generation of the resonant emission ( 3 d ~ / ~ 4 f ~ + ~ + 3 d l 4fn), where n is equal to 5 for the sm3+ ion. The hole-induced shakedown process was observed in the M4,5 fluorescent emission spectrum of La metal.
The electronic energy states of rare earths and their compounds have become a subject of much interest in recent years because of the rather diverse electrical and magnetic properties of these substances /I/. It has been known that such properties are attributed to the unfilled 4f level which is localized around the rare-earth ion. The properties of samarium hexaboride SmB6, which is known to be a homogeneous mixed-valence compound, have been studied extensively by many experimental techniques, and the mixed-valence character of this substance has been discussed
/2-7,'.Crecelius et al. /8/ have found
ashakedown satellite in the 3d5/2 x-ray photoelectron spectrum (XPS) of La metal and interpreted it as the 3d5/2 line when the 4f level, which is empty in the ground state, is filled by an electron from the conduction-band states in the presence of a 3d core hole.
In the present work, we measured the Sm M4.5 emission spectrum with various electron-beam energies near the Sm 3d5/2 threshold and also the characteristic isochromat spectrum on Sm metal and SmBg to obtain the information on .the excitation threshold of the emission lines by electron impact
/9/.Moreover, the M4 5 emission spectrum of La metal was measured with the fluorescence excitation method'to observe the x-ray emission from the excited configuration and to confirm the possibility of a hole-induced shakedown transition /lo/.
EXPERIMENTAL PROCEDURE
The electron-excited M4,5 emission and isochromat spectra were obtained with a
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19879162
JOURNAL DE PHYSIQUE
f l a t c r y s t a l vacuum s p e c t r o m e t e r e q u i p p e d w i t h a f i n e S o l l e r s l i t and a p o t a s s i u m a c i d p h t h a l a t e c r y s t a l . The s p e c t r a l window i s a b o u t 2.5 eV i n t h e Sm M4,5 s p e c t r a l r e g i o n . I n t e n s i t y measurements were c a r r i e d o u t a u t o m a t i c a l l y f o r a p r e s e t c o u n t i n g t i m e a t a r e g u l a r i n t e r v a l o f O.O1° o f t h e Bragg a n g l e b y means o f a s t e p - s c a n n i n g method. The d e t e c t o r was a g a s - f l o w p r o p o r t i o n a l c o u n t e r equipped w i t h a t h i n p o l y p r o p y r e n e window and an a r g o n gas w i t h 10% o f methane b y volume. Specimens o f Sm m e t a l and SmB6 were p r e p a r e d b y e v a p o r a t i o n o n t o a c o p p e r anode.
F o r t h e measurement o f t h e f l u o r e s c e n t Mq.5 e m i s s i o n spectrum o f La m e t a l , a rhodium t a r g e t x - r a y t u b e o p e r a t e d a t 40 kV and 70 mA was used as a p r i m a r y source.
I n t h i s case. specimen o f La m e t a l was p r e p a r e d b y e v a p o r a t i o n o n t o an aluminum s u b s t r a t e and c o v e r e d b y a t h i n aluminum f i l m .
RESULTS AND DISCUSSION
The Sm M4,5 e m i s s i o n s p e c t r a o f Sm m e t a l and SmB6 o b t a i n e d w i t h v a r i o u s i n c i d e n t electron-beam e n e r g i e s a r e shown i n F i g s . 1 and 2, r e s p e c t i v e l y . The a r r o w s i n d i c a t e t h e e n e r g i e s o f t h e i n c i d e n t e l e c t r o n beam. The s p e c t r a o f SmB6 e x h i b i t t h e s i m i l a r f e a t u r e s as t h o s e o f Sm m e t a l i n s p i t e o f t h e mixed-valence c h a r a c t e r o f SmB6. I n t h e spectrum e x c i t e d w i t h t h e electron-beam energy o f 1500 eV, t h e e m i s s i o n peaks R (1079 eV) and R' (1105 eV), w h i c h c o i n c i d e w i t h t h e a b s o r p t i o n pegks ( 6 / , a r e a s s i g n e d as t h e r e s o n a n t e m i s s i ns caused b y t h e t r a n s i t i o n 3d 4 f n f -3d104fn, where n i s e q u a l t o 5 f o r t h e smgc i o n . The peak F (1075 ev), w h i c h b e g i n s t o r i s e a t t h e e x c i t a t i o n e n e r g y o f a b o u t 1083 eV, g r a d u a l l y i n c r e a s e s i t s i n t e n s i t y and t h e n b u r i e d i n t h e t a i l o f t h e r e s o n a n t peak w i t h t h e i n c r e a s e o f t h e e x c i t a t i o n energy. To see t h e o n s e t o f t h e i n t e n s i t y r i s e o f t h i s peak we measured t h e c h a r a c t e r i s t i c i s o c h r o m a t s p e c t r a a t t h e p h o t o n e n e r g y o f t h e peak F a t 1075 eV on Sm m e t a l and SmB6. The r e s u l t s a r e shown i n F i g s . 3 and 4 t o g e t h e r
2% 4 1072 eV
1050 1100
PHOTON ENERGY (eV)
F i g . 1 - Sm Mq,5 e m i s s i o n s p e c t r a o f Sm m e t a l o b t a i n e d w i t h v a r i o u s e l e c t r o n - beam e n e r g i e s .
I ~ ~ t C . , ~ t ~ ~ ~ l
1050 1100
PHOTON
ENERGY (eV)F i g . 2 - Sm M4.5 e m i s s i o n s p e c t r a of Sm66 o b t a i n e d w i t h v a r i o u s e l e c t r o n - beam e n e r g i e s .
w i t h t h e s p e c t r a o b t a i n e d a t t h e p h o t o n e n e r g y o f t h e peak R a t 1079 eV. The i n t e n s i t y o f t h e peak f a t 1075 eV c l e a r l y b e g i n s t o r i s e a t t h e e l e c t r o n - beam e n e r g y beyond t h e 3d5 2 t h r e s h o l d (1082.2 eV) o f t i e
sm3+
i o n . Moreover, t h e e n e r g y o f t h i s peak (1075 eV) agrees w e l l w i t h t h e b i n d i n g - e n e r g y d i f f e r e n c e between t h e o c c u p i e d 4 f and t h e 3d5/2 l e v e l s o f t h e sm3+ i o n o b t a i n e d f r o m t h e XPS d a t a 131. Thus, we a t t r i b u t e t h i s peak F t o t h e o r d i a rti
M5N6,7 1 & m i 2 s i o n l i n e 3d 4 f -3d 4 f ) o f t h e Sml+ i o n . The p o s i t i o n F ' can be a s s i g n e d as t h e o r d i n a r y M4N6 e m i s s i o n b y knowing t h e s p i n - o r b i t s p l i t t i n g o f t h e 3d l e v e l t o be 25.8 eV.
The c h a r a c t e r i s t i c i s o - chromat s p e c t r a measured a t t h e p h o t o n e n e r g y o f 1079 eV, i
.
e.,a t t h e p o s i t i o n o f t h e r e s o n a n t peak R o f t h e ~ m 3 + i o n , e x h i b i t t h a t t h e i n t e n s i t y o f t h i s peak r i s e s a t t h e electron-beam e n e r g y beyond 1085 eV i n c o n t r a s t t o t h e p h o t o a b s o r p t i o n p r o c e s s . T h i s d e l a y e d o n s e t o f t h e i n t e n s i t y r i s e may be a t t r i b u t e d t o t h e c r e a t i o n o f t h e t r a n s i e n t t a e w i t h t h e c o n f i g u r a t i o n 3d44f5, w h i c h i s caused b y b o t h t h e e l e c t r o n e x c i t e d f r o m t h e 3d l e v e l and t h e i n c i d e n t e l e c t r o n
L a8 . . I
....
0....
I . . . . ,....
' . . . . I . . . u ~1080 1100 1120
EXCITATION ENERGY (eV)
F i g . 3 - C h a r a c t e r i s t i c i s o c h r o m a t s p e c t r a measured a t t h e p h o t o n e n e r g i e s o f 1075 eV (F, s o l i d l i n e ) and 1079 eV (R, dashed l i n e ) on Sm m e t a l .
l o s i n g t h e i n i t i a l e n e r g y due
t o t h e i n e l a s t i c c o l l i s i o n . 1080 1100 1120
S i n c e t h i s s t a t e may be l o c a t e d EXCITATION ENERGY (eV)
w e l l above t h e Fermi l e v e l , F i g . 4 - C h a r a c t e r i s t i c i s o c h r o m a t s p e c t r a t h e i n t e r a c t i o n o f t h i s s t a t e - measured a t t h e p h o t o n e n e r g i e s o f 1075 eV (F, w i t h t h e empty c o n t i n u u m s t a t e s s o l i d l i n e ) , 1079 eV (R, dashed l i n e ) and 1071 m i g h t i m m e d i a t e l y c r e a t e t h e eV ( d o t t e d l i n e ) on SmB6.
i n i t i a l s t a t e ( 3 d 9 4 f 6 ) o f t h e r e s o n a n t e m i s s i o n o f t h e sm3+
i o n , whose e n e r g y (1079 eV i s l p t e r t h a n t h e 3d5/2 t h r e s h o l d (1082.2 eV). Then,
9 2
t h e r e s o n a n t e m i s s i o n 3d 4 f +3d 4 f 5 occurs. Thus, we b e l i e v e t h a t t h e e n e r g y o f 1085 eV i s n e c e s s a r y a t l e a s t f o r t h e e x c i t a t i o n o f t h e r e s o n a n t e m i s s i o n b y e l e c t r o n impact.
The c h a r a c t e r i s t i c i s o c h r o m a t spectrum o f SmBg a t t h e p h o t o n e n e r g y o f 1071 eV, w h i c h i s t h e b i n d i n g - e n e r g y d i f f e r e n c e between t h e f i l l e d 4 f and t h e 3d5/2 l e v e l s o f t h e sm2+ i o n o b t a i n e d f r o m t h e XPS d a t a 131, was mea u r e d i n o d e r t o c n f i r m whether t h e o r d i n a r y e m i s s i o n due t o t h e t r a n s i t i o n 3d94f8-+3d104f5 i n t h e srn" i o n i s observed o r n o t . However, t h e i n t e n s i t y o f t h i s spectrum does n o t i n c r e a s e a p p r e c i a b l y even i f t h e i n c i d e n t - e l e c t r o n - b e a m e n e r g y i s beyond t h e 3d5/2 b i n d i n g e n e r g y o f t h e ~ m 2 + i o n (1071.3 eV). T h i s f a c t may s u g g e s t t h a t t h e c o n t r i b u t i o n o f t h e o r d i n a r y MgNg, 7 e m i s s i o n o f t h e sm2+ i o n i s t o o s m a l l t o be o b s e r v e d o r a v a l e n c e change o c c u r s f r o m d i v a l e n t t o t r i v a l e n t u n d e r t h e e l e c t r o n i m p a c t .
C9-918 JOURNAL DE PHYSIQUE
The f l u o r e s c e n t M4.5 e m i s s i o n s p e c t r u m o f La m e t a l i s shown i n F i g . 5 t o g e t h e r w i t h t h e e l e c t r o n - e x c i t e d s p e c t r a w i t h v a r i o u s electron-beam e n e r g i e s . The M4,5 a b s o r p t i o n spectrum measured b y M a r i o t and K a r n a t a k /11/
i s a l s o shown b y a dashed l i n e . I n t h e s p e c t r a ( c ) and ( d ) , t h e peaks R and R' may be a s c r i b e d t o t h e r e s o n a n t e m i s s i o n 3d94f1
-
3d1°4f0 because t h e e n e r g y p o s i t i o n s o f t h e s e peaks c o i n c i d e w i t h t h o s e o f t h e a b s o r p t i o n peaks. The g e n e r a l f e a t u r e o f t h e f l u o r e s c e n t e m i s s i o n spectrum ( a ) resembles t h a t o f t h e spectrum ( b ) w h i c h was o b t a i n e d w i t h t h e e l e c t r o n e x c i t a t i o n method w i t h t h e e l e c t r o n - beam e n e r g y o f 10.0 keV and s u f f e r e d t h e s e l f - a b s o r p t i o n e f f e c t . I n t h e p r e s e n t f l u o r e s c e n t spectrum r a t h e r - h i g h - e n e r g y p h o t o n s (Rh L) were i r r a d i a t e d on t h e specimen so t h a t a 3d c o r e e l e c t r o n i s m e r e l y e x c i t e d f a r i n t o t h e continuum, and t h u s t h e r e i s no p o s s i b i l i t y o f t h e r e s o n a n t e m i s s i o n caused by t h e same o r i g i n as w i t h t h e e l e c t r o n e x c i t a t i o n method. However, t h i s r e s u l t i n d i c a t e s t h a t t h e shakedown t r a n s i t i o n f r o m t h e c o n d u c t i o n - band s t a t e s t o t h e empty 4 f l e v e l o c c u r s i n t h e p r e s e n c e o f a 3d c o r e h o l e as p o i n t e d o u t b y C r e c e l i u s e t a l . /8/ Also, t h e s a t e l l i t e S was ob e r v d on t h l o w e n e r g y s i d e o f t h e
ti
M503 (3d FJjZ4fp -)5pi/24f0) d i a g r a m 1 in e D and a t t r i b u t e d t o t h e t r a n s i t i o n 3dgJ24f1 +- 5 p j j 2 4 f 1 . T h i s g i v e s f u r t h e r e v i d e n c e o f t h e h o l e - i n d u c e d shakedown t r a n s i t i o n . I t i s n o t i c e d t h a t t h e i n t e n s i t y o f t h e l o w b i n d i n g e n e r g y s a t e 1 l i t e i n t h e 3d5/2 XPS o f r a r e e a r t h s decreases f r o m La t o Nd as t h e o v e r l a p between t h e i n c r e a s i n g l y c o r e - l i k e 4 f and c o n d u c t i o n e l e c t r o n s decreases 18. 121. Thus, i n Sm m e t a l and SmBg t h e shakedown e f f e c t s s h o u l d be n e g l i g i b l y s m a l l .
800 900
PHOTON ENERGY (eV)
Fig. 5 - M4,5 s p e c t r a o f La m e t a l . Spectrum ( a ) i s t h e f l u - o r e s c e n t spectrum. S p e c t r a (b).
( c ) and ( d ) a r e t h e e l e c t r o n - e x c i t e d s p e c t r a o b t a i n e d w i t h t h e electron-beam e n e r g i e s o f 10.0, 5.0 and 1.5 keV, r e s p e c - t i v e l y . The M4 5 a b s o r p t i o n s p e c t r u m measured b y M a r i o t and K a r n a t a k /11/ i s a l s o shown b y a dashed l i n e .
REFERENCES
/I/ C. M. Varma, Rev. Mod. Phys.
48,
219 (1976)./2/ A. Menth, E. B u e h l e r and T. H. Geballe, Phys. Rev. L e t t .
22,
295 (1969)./3/ M. Aono, S. Kawai, S. Kono, M. Okusawa, T. Sagawa and Y. Takehana, S o l i d S t a t e Commun.
16,
1 3 (1975)./4/ M. Okusawa, Y. I w a s a k i , K. Tsutsumi, M. Aono and S. Kawai, Jpn. J. Appl. Phys.
17, Suppl. 17-2, 161 (1978).
/5/ -N. C h a z a l v i e l , M. Campagna, G. K. Wertheim and P. H. Schmidt, Phys. Rev. B 14, 4586 (1976).
/6/ A i t a , T. Watanabe, Y. F u j i m o t o and K. Tsutsumi, J. Phys. Soc. Jpn.
51,
483(1982).
/7/ K. Tsutsumi, 0. A i t a and T. Watanabe, Phys. Rev. B
25,
5415 (1982)./8/ G. C r e c e l i u s , G. K. Wertheim and D. N.
E.
Buchanan, Phys. Rev. B18,
6519 ( 1 978)./9/ 0. A i t a , K. Ichikawa, M. Okusawa and K. Tsutsumi, Phys. Rev. B
34,
8230 (1986)./lo/
M. Okusawa, K. Ichikawa, 0. A i t a and K. Tsutsumi, Phys. Rev. B35,
478(1978-I)./11/ J. M. M a r i o t and R. C. Karnatak, J. Phys. F
4,
L223 (1974)./12/ G. K. Wertheim. "Valence F l u c t u a t i o n s i n S o l i d s " , e d i t e d b y L. M. F a l i c o v , W.
Hanke and M. B. Maple (North-Holland, Amsterdam, 1981) p. 67.
