Synchrotron-radiation Spectroscopy Study of the La

P ê

s V R Ë T ú n Þ @ _z º¬ Ž­ Ž T ² Ž  ˜ m× Dö n Ú La

MnNiO

8 ý U ê s ° Ë Ñ Ä Z Ø° Ë Ñ Ž ì ŏ Œ

™

»½‘S · Tg`@.> · T„ç¡`9 · ~ç¡+䬣^∗

d¦aË:@/†<Ɠ§ Óüto†<Æõ, Â҅; 420-743

B. Dabrowski

Northern Illinois University, DeKalb, Illinois 600115, U.S.A.

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DzDG³ðïrõ†<ƃ½¨"é¶, @/„ 305-340

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Â6Ò@žB · ™»<*å

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톽Ó5Åqlƒ½¨™è, Ÿí†½Ó 790-748 (2007¸ 8Z4 20{9 ~ÃÎ6£§)

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 x‚ %ò%i_ ~½ÓFg`¦ s6 x #Œ La2MnNiO6 y©œ$í s×æ `…–ÐÚÔÛ¼sàÔ íߖoÓüt[þt\ @/ #Œ Fg f



¨Ãº ìrFg (x-ray absorption spectroscopy: XAS) z´+«>õ Fg„ ìrFg (photoemission spectroscopy:

PES) z´+«>`¦ ú'Ÿ %i. T 2p XAS (T=Mn, Ni) Û¼&7˜àÔ!3_ 8£¤&ñ`¦ :Ÿx #Œ @/ÂÒìr_ Mn s“:r[þt õ

 Ni s“:r[þt“Ér yŒ•yŒ• Mn⁴⁺ü< Ni²⁺_ ©œI\ e”H כ `¦ ·ú˜ ú e”%3. Õªo“¦ T 2p → 3d f¨Ãº H

%

ƒ\"f_ /BN"î Fg„ ìrFg z´+«> õ–Ð ÂÒ' Mn 3d ©œIH `…ØÔp ïr0A–ÐÂÒ' €• 2 eV A\ 0A u

 “¦ e”H ìø̀, Ni 3d ©œIH `…ØÔp ïr0A–ÐÂÒ' €• 3 eV A\ Áº> ×æd”s e”ܼ 9 Mn 3d ©œI

\

 q #Œ Bĺ V,“Ér %ò%i\ 5g ìrŸí÷&#Q e”H כ `¦ µ1Ï| %i. sQôÇ µ1Ï|“Ér La2MnNiO6 \

"

f Ni 3d „[þtõ O 2p „[þt çߖ_ ™D¥$í ©œ ñŒ•6 xs Bĺ ß¼H כ `¦
·p.

PACS numbers: 78.70.Dm, 79.60.-i, 74.25.Jb, 75.50.Dd

Keywords: y©œ$í s×æ `…–ÐÚÔÛ¼sàÔ íߖoÓüt, Fgf¨ÃºìrFg, Fg„ìrFg, „½¨›¸

I. "e Â]Ø

þ

jH Sr2FeMoO6+þA_ s×æ `…–ÐÚÔÛ¼sàÔ (double perovskite) ½¨›¸\¦ ” íߖoÓüt\"f Z}“Ér y©œ$í „s

“ :

r•¸ (3'o “:r•¸: Tc=415 K) ›'a¹1Ï÷&%3ܼ 9, ©œ“:r\"f

± ú

“Ér l©œ`¦ K•¸ l $†½Ó (magnetoresistance : MR) ´òõ
èߖH כ s µ1Ï|÷&%3 [1]. sQôÇ µ1Ï

|

ܼ–Ð “ #Œ A2BB⁰O6 (A: 2 "鶙è; B,B⁰: „sFK5Åq

"

é

¶™è) +þA_ s×æ `…–ÐÚÔÛ¼sàÔ íߖoÓüt\ @/ #Œ ´ú§“Ér

ƒ



½¨ ˜Ð“¦÷&%3ܼ
 Z}“Ér Tc_ "鶓\ @/K"fH f”

•

¸ 7HêøÍs e”H z´&ñs. tFKt ƒ½¨)a œí@/l

$

†½Ó (colossal magneto-resistance : CMR) Óüt|9[þt“Ér ÅÒ

–

Ð `…–ÐÚÔÛ¼sàÔ ½¨›¸\¦ ” AMnO3 +þA_ Mn íߖo Ó

ü

ts%3ܼ 9, s[þts
?/H œí@/l$†½Ó ‰&³©œ, y©œ

∗E-mail: [email protected]



$íõ FK5Åq$í_ :£¤$í“Ér s×æ “§¨8Š (double exchange) ©œ  

ñŒ•6 xܼ–Ð sK÷&%3 [2]. A2BB⁰O6+þA_ s×æ `…–ÐÚÔ Û

¼sàÔ íߖoÓüt“Ér Bü< B⁰ o\ yŒ•yŒ• "é¶ Ér

„



sFK5Åq (transition metal) "鶙è–Ð G0>4R e”“¦ s[þt“Ér 6>h_ íߖ™è–Ð ÑütQ “ &ñ¼1π^‰ ½¨›¸\¦ sÀғ¦ e” [1]. A2FeMoO6 (A=Sr, Ba) +þA_ s×æ `…–ÐÚÔÛ¼sàÔ í

ß

–oÓüt_ âĺ Fe s“:r[þts Fe²⁺-Fe³⁺_ ™D¥½+Ë"é¶ ©œ I

\ e”H z´s µ1Ï|÷&%3ܼ 9, "f s[þt íߖoÓüt

\

"f_ y©œ$í ]XìøÍFK5Åq$í (half-metallic) ‰&³©œ_ "鶓ܼ

–

Ð Fe³⁺-Mo⁵⁺ ü< Fe²⁺-Mo⁶⁺ s_ {97áx_ s×æ “§¨8Š



©

œ ñ Œ•6 xs ×æכ¹½+É כ s“¦ \V8£¤)a  e” [3].

LaMn0.5Ni0.5O3 ü< La2MnNiO6 H ©œ{©œy Z}“Ér y©œ

$ í

„s“:r•¸ (Tc=280 K)\¦ ” [4–7]. La2MnNiO6

_

 $í ‰&³©œ\ @/K"fH ß¼> ¿º t _|s e”HX<, Õ

ª ×æ ôÇ _|“Ér La2MnNiO6\"f Áº|9"f > C\P)a ±ú

“ É

r Û¼—2; (low- spin) ©œI_ Ni³⁺s“:rõ Mn³⁺s“:r[þts -212-

"

f–Ð ”1lx&h œí“§¨8Š ©œ ñŒ•6 x (vibronic super-exchange)

`



¦ “¦ e”H כ s [4]. ¿º P: _|“Ér La2MnNiO6

\

"f Ni²⁺ s“:rõ Mn⁴⁺ s“:r[þts &ñ§>=)a ©œI–Ð e”





H _|s [5]. ÕªQÙ¼–Ð La2MnNiO6 +þA_ s×æ `…–Ð Ú

ÔÛ¼sàÔ íߖoÓüt\"f „sFK5Åq s“:r[þts #Q‹" "é¶

\



¦ t“¦ e”Ht z´+«>&hܼ–Ð &ñ H כ “Ér s Óüt|9[þt _

 $í_ "鶓`¦ sK HX< Bĺ ×æכ¹  ’x.

s

 ƒ½¨\"fH ~½ÓFg`¦ s6 xôÇ ƒ x‚ Fgf¨Ãº ìrFg Z

O

 (soft x-ray absorption spectroscopy: XAS)õ Fg„ ì

rFgZO (photoemission spectroscopy: PES)`¦ s6 x #Œ La2MnNiO6 _ y©œ$í s×æ `…–ÐÚÔÛ¼sàÔ íߖoÓüt_

„



½¨›¸\¦ ƒ½¨ %i. Fgf¨Ãº ìrFgZOõ Fg„ ìrFg Z

O

“Ér “¦^‰_ „½¨›¸\¦ f”]X 8£¤&ñ½+É Ãº e”H Ä»6 xôÇ z´ +

«

> ~½ÓZOs [3,8,9]. La2MnNiO6_ Mn 2p XAS Û¼&7˜àÔ

! 3

õ Ni 2p XAS Û¼&7˜àÔ!3`¦ 8£¤&ñ†<Êܼ–Ð+‹ Óüt|9 ?/\"f Mnõ Ni s“:r_ "é¶ #Q‹" ©œI–Ð ”>rF Ht\¦ 

&

ñ

%iܼ 9, Z}“Ér ynC\-t %ò%i_ ~½ÓFg`¦ s6 xôÇ 

„



 { Fg„ ìrFg z´+«>`¦ :ŸxK G0>4R e”H Mn 3d, Ni 3d, O 2p „[þt_ \-t ìrŸí\¦ &ñ %i.

II. ÷mÇ ]Mö

s

 ƒ½¨\ 6 xôÇ r«ÑH La2MnNiO6y©œ$í s×æ `…

–

ÐÚÔÛ¼sàÔ íߖoÓüt &ñ (polycrystalline) r«Ñ%i.

XASü< PES z´+«>“Ér Ÿí†½Ó 5Åql ƒ½¨™è (Pohang Accel- erator Laboratory: PAL)_ 2A c”“\"f sÀÒ#Q&’.

8

£

¤&ñ r ìr$3 $כ›!Q_ ”/BN“Ér €• 1 × 10⁻¹⁰ Torr_ œí“¦” /

B

N ©œI%iܼ 9, r«Ñ[þt_ “:r•¸H €• 20 K s%3. XAS 8

£

¤&ñ\H ‚+þA ¼#Fg)a ynC`¦ 6 x %iܼ 9, XAS Û¼&7˜àÔ

! 3

\"f_ \-t ìrK0px“Ér hν ∼ 600 eV \"f €• ∼ 100 meV &ñ•¸%i. „ { PES Û¼&7˜àÔ!3\"f_ `…ØÔp ï

r0A (Fermi level: EF)ü< \-t ìrK0px (energy resolu- tion)“Ér Pd FK5Åq_ `…ØÔp ïr0A H%ƒ_ Û¼&7˜àÔ!3ܼ–Ð 

&

ñ

%iܼ 9, 8úx ìrK0px“Ér €• 150 meV &ñ•¸%i.

La2MnNiO6 íߖoÓüt r«Ñ[þt_ 8£¤&ñ ³ð€“Ér œí“¦”/BN ì

r$3 $כ›!Q 5Åq\"f r«Ñ[þt`¦ scraping`¦ #Œ ïrq %i



. r«Ñ ³ð€_ L:FMôÇ &ñ•¸H O 1s ?/yŒ•ïr0A Û¼&7˜àÔ!3 _

 —¸€ªœ`¦ ˜Ð“¦ &ñ %iܼ 9, 1lxr\ „ { PES Û¼

&

7

˜àÔ!3\"f ½+Ë\-t (binding energy) €• ∼ 9 eV\"f bump ›'a¹1Ï÷&t ·ú§HH z´–Ð ÂÒ' ³ð€s Ô¦íHÓüt s

 \Os L:FM†<Ê`¦ ·ú˜ ú e”%3.

Fig. 1. Mn 2p XAS spectra of La2MnNiO6, in compari- son to those of reference Mn oxides

III. ÷mÇ]Mö +sÇÊÝ õmÍ wŠ²o

1. T 2p XAS (T=Mn, Ni) ŽìŏŒ

Fig. 1“Ér La2MnNiO6 _ Mn 2p → 3d –Ð_ „s\ _ ô



Ç Mn 2p XAS Û¼&7˜àÔ!3`¦ ˜Ð#Œ ïr. La2MnNiO6\"f Mn s“:r[þts #Q‹" "é¶ ©œI\ e”Ht ·ú˜l 0A #Œ "î 3

l

q©œ_ "é¶ (nominal valence) yŒ•yŒ• Mn²⁺, Mn³⁺, Mn⁴⁺ ©œI“ Mn²⁺O [10], Mn³⁺₂ O3 [11], Mn⁴⁺O2 [10]

1 p

x_ Mn íߖoÓüt[þtõ q“§ %i. #Œl"f La2MnNiO6

_

 Mn 2p XAS Û¼&7˜àÔ!3s MnO2 _ Mn 2p XAS Û¼

&

7

˜àÔ!3õ Bĺ Ä»ôÇ כ `¦ ·ú˜ ú e”HX<, sQôÇ µ1Ï|

“ É

r La2MnNiO6 ?/\"f Mn s“:r[þts _ Mn⁴⁺ (3d³: t³_2g ↑) ©œI–Ð ”>rFôǍH כ `¦
·p. s ÕªaË>\"f

˜

Ѐ Mn²⁺ _ $íìrs €•çߖ [O#Œ e”H כ `¦ ·ú˜ ú e”H X

<, Õª "鶓“Ér "îSX‰ t ·ú§Ü¼
, ³ð€\ ™è|¾Ó_ Ô¦íHÓüt s

 ”>rF l M:ëHs
 x=0 _ r«Ñ\"f O "鶙è_ ‘



o (vacancy) Òqtl M:ëH{9 ú e”’x.

Fig. 2(a)H La2MnNiO6 \"f La 3d → 4f „s %ò

% i

õ Ni 2p → 3d „s %ò%i_ Fgf¨Ãº Û¼&7˜àÔ!3`¦ ˜Ð#Œ ï

r. ĺ‚ La 3d XAS ÂÒìr`¦ La2O3 (La³⁺)ü< q“§ 

% i

HX< [12], s q“§–ÐÂÒ' La2MnNiO6 ?/\"f La s

Fig. 2. (a) Comparison of the La 3d and Ni 2p XAS spectra of La2MnNiO6 and La2O3. (b) The extracted Ni 2p XAS spectrum of La2MnNiO6, compared to those of reference Ni oxides.

“ :

r[þt“Ér _ La³⁺ ©œI–Ð ”>rFôǍH כ `¦ ·ú˜ ú e”.

ô



Ǽ# Fig. 2(a)\"f ·ú˜ ú e”H ü< °ú s La 3d → 4f

„



s {9#Q
H ynC \-tü< Ni 2p → 3d „s {9#Q

H ynC \-t "f–Ð ul M:ëH\ La2MnNiO6 \

"

f Ni 2p XAS Û¼&7˜àÔ!3_ ‚—¸€ªœ`¦ ·ú˜l ~1t ·ú§.

Õ

ªQÙ¼–Ð s ƒ½¨\"fH La2O3_ La 3d XAS Û¼&7˜àÔ

! 3

`¦ ‚ÃГ¦ Û¼&7˜àÔ!3ܼ–Ð 6 x #Œ La2MnNiO6 _ XAS Û

¼&7˜àÔ!3õ La2O3_ XAS Û¼&7˜àÔ!3õ_ s\¦ ½¨†<Êܼ

–

Ð+‹ La 3d f¨Ãº\ _ôÇ l#Œ\¦ ]j %iܼ 9, s s

\



¦ La2MnNiO6 _ Ni 2p XAS Û¼&7˜àÔ!3ܼ–Ð K$3 %i



. sXO> ½¨ôÇ La2MnNiO6 _ Ni 2p XAS Û¼&7˜àÔ!3

`



¦ ÕªaË> 2(b)\"f ˜Ð#Œ ïr. Ö¦Q Ni²⁺ ©œIü< Ni³⁺



©

œI_ ‚ÃГ¦ Óüt|9–Ð NiO (Ni 2+) [13] ü< PrNiO3 (Ni 3+) [14] _ Ni 2p XAS Û¼&7˜àÔ!3[þtõ q“§ %i. Õª a

Ë

> 2(b)\¦ ˜Ð€ La2MnNiO6 _ Ni 2p Û¼&7˜àÔ!3s NiO_ Ni 2p Û¼&7˜àÔ!3õ Bĺ Ä»ôÇ כ `¦ ·ú˜ ú e”HX<, s–Ð Â

Ò' La2MnNiO6 ?/\"f Ni s“:r[þt“Ér _ Ni²⁺ (3d⁸: t³_2g↑ e²_g↑ t³_2g↓)_ ©œI–Ð ”>rFôǍH כ `¦ ·ú˜ ú e”.

Fig. 3. Comparision of the valence-band energy distri- bution curves (EDC’s) of La2MnNiO6.

2. ¹Å + ŒŸ«ã_Ë °Ëя¹Å ÄZØ°ËÑ ŽìŏŒ /

B

N"î Fg„ ìrFgZO (resonant photoemission spec- troscopy: RPES)“Ér „sFK5Åq s“:r_ 2p → 3d f¨Ãº H%ƒ

\

"f ›'a¹1Ï÷&H 3d Fg„ ~½Óئ_ /BN"î ‰&³©œ`¦ s6 xôÇ [3]. sQôÇ /BN"î Fg„ ìrFgZO`¦ s6 x € T (T=Mn, Ni) 3d š¸q_O_ \-t ìrŸí\¦ &ñ½+É Ãº e”. Fig. 3“Ér

@

/³ð&h“ Y>Y> ynC \-t\"f 8£¤&ñôÇ La2MnNiO6_ 

„



 { (valence band)_ \-t ìrŸí /BG‚ (energy dis- tribution curve: EDC)`¦
·p כ s. ynC \-t  7

€"f „ { PES Û¼&7˜àÔ!3_ —¸€ªœs ²ú˜tH s Ä

»H ynC\-t 7 € yŒ• ïr0A\"f ~½Óئ÷&H „_

~

½

Óئ SX‰Ò¦\ K{©œ H Fgs“:ro éߖ€&h (photoionization cross-section) s ²ú˜tl M:ëHs [15]. ÕªQÙ¼–Ð „



 { PES Û¼&7˜àÔ!3[þt_ ‚—¸€ªœ`¦ ìr$3½+É M: sQôÇ  z



´`¦ “¦9K ôÇ.

#

Œl"f hν=641 eV ü< hν=853 eV H yŒ•yŒ• Mn 3d Fg

„



 ~½Óئ_ /BN"îõ Ni 3d Fg„ ~½Óئ_ /BN"îs {9#Q






H \-t\ K{©œôÇ. Õªo“¦ hν=520 eV H sQôÇ /BN

"

î

‰&³©œs {9#Q
H \-t\"f YOo b#Q” \-t\ K

{©œôÇ. ÕªQÙ¼–Ð hν=520 eV \"fH Mn 3d, Ni 3d,