STRUCTURE AND MAGNETIC BEHAVIOR OF Zn 1 x Co x O CRYSTAL POWDERS PREPARED BY SOL GEL TECHNIQUE

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1 47 3 Vol.47 No ACTA METALLURGICA SINICA Mar pp ½ ¼ Å Zn 1 x Co x O ²Æ º¹µ (ß Õ Õ, Äß ) Á Ë Zn 1 xco xo(x= , µ Ö) ĐÑ Ý, Á XRD, TEM Ã SEM Ã Ë±ÁÃ. ±Õ, ¹ Â º 100 nm Ñ ¾Ä, Zn 1 xco xo Ñ Ö¹ ± Ñ ZnO Ö, ÀË ZnO, Ô «Ø «. Î Ñ, Đ³ ÆÎ. Å, ¼Ý ÆÎ»ÍÑ ÁÔ, O ÆÎ Ù Ñ «, Ä Ñ ÆË ÑÎ., Zn 1 xco xo, ÆÎ ³ O472.5, O482.5 A ¾ (2011) STRUCTURE AND MAGNETIC BEHAVIOR OF Zn 1 x Co x O CRYSTAL POWDERS PREPARED BY SOL GEL TECHNIQUE GAO Qian, SUN Benzhe, QI Yang, QI Lianzhong College of Sciences, Northeastern University, Shenyang Correspondent: QI Yang, professor, Tel: (024) , qiyang@imp.neu.edu.cn Supported by Science Research Program of Liaoning Province (No ) and Shenyang Municipal Science Research Program (No ) Manuscript received , in revised form ABSTRACT ZnO based diluted magnetic semiconductors (DMSs) have been considered as one of the promising candidates for fabricating DMSs due to their initial prediction in theory of having the Curie temperature greater than room temperature, its high solubility for transition metals, and its superior semiconductor properties. Recently, Co substituted ZnO DMSs were reported frequently to show ferromagnetic properties at room temperature. However, various subsequent studies do not seem to converge on the origin of room temperature ferromagnetism. Among the controversy, Co cluster, Co oxides and substitutions of Co for Zn are typical viewpoints. Meanwhile, it is not completely understood how the fabricating process influence the magnetic properties of Co doped ZnO DMS. For this purpose, relationships among Co doping concentration, sintered temperature, microstructure and magnetic properties of ZnO need to be invesigated particularly. In this paper, Zn 1 x Co x O (x=0.01, 0.02, 0.03, 0.04 and 0.05, atomic fraction) nanocrystal powders were prepared by sol gel technique. The crystal structure, lattice parameters, morphology and composition were characterized and analyzed by XRD, TEM, SEM and EDS, respectively. The magnetic properties were examined at room temperature using a vibrating sample magnetometer (VSM). It can be found that all the samples are composed of the particles with hexagonal wurtzite structure and the sizes of the particles are about 100 nm. For all synthesized Zn 1 x Co x O samples, the lattice constants are smaller than those of un doping ZnO crystals under the condition of the same sintered temperature. It indicates Co 2+ ions have substituted Zn 2+ sites. All the samples exhibit room temperature ferromagnetic characteristics, and the ferromagnetism * ÊÅÉ ÑÍÈ ÃÅ ÑÍÈ Æ : , : Ù Ú«: Ü, Æ, 1963 Æ, ÞË, Æ DOI: /SP.J

2 338 Ó Ô 47 is their intrinsic attribute, in which the Zn 0.98 Co 0.02 O sample sintered at 500 and 700 has the highest coercivity (H c ) of Gs and the highest remanent magnetization ratio (M r /M s ) of , respectively, and the Zn 0.96 Co 0.04 O sample sintered at 950 has the maximum magnetic energy product (BH) of J/kg and saturation magnetization (M s ) of Am 2 /kg. The magnetic behaviors of these samples vary not only with the concentration of Co, but also with the size of crystal grains and the concentration of oxygen vacancies. It can be found that the moderate Co content and the larger size of crystal grains are in favour of increasing room temperature ferromagnetic characteristics. Meanwhile, as far as the same concentration of Co is concerned, the smaller volume of the cell contributes to increase room temperature ferromagnetism. KEY WORDS sol gel technique, Zn 1 x Co x O, room temperature ferromagnetism ZnO Ò¼Î Å Ò [1,2], «ÕÏ Õ Ü ZnO µò [3], Ö Dietl Ô [4] ³ ZnO Ï ¼Î µ Ò Curie, Õ Õ Ü ZnO ¼ÎÒÚ Î ½ [3 18]. Ú [5,6] ²Ö, Co ZnO ¼Î Ü ¼ Ï. Ì Co ZnO Ï ÒÚ [5 13], Ï Ò¼ Í. Ú [7,8] Ý Co ZnO Ò Ï Co Õ Co ÒÐÎ, «Ú [9 13] Co «Å Zn Ò ZnO, Ï Õ ÂÕ. Co Ò Ó Ï ZnO Ú ÒÑ, «ÌÏ, «ÖÝÜ Ò ÐÓ ÜÁ Æ, Æ Ï ¼ÎÒ ÁÒ Å., Ú [8] Co ZnO ¼ÎÒÏ»Þ Ä Õ, ²Ö Æ ¹ ½ Ò Î ¼ÎÏ Ò±. Sayak Ä Anil [14] ¾ Î Ò ¼Î, ² Ð Ï² ÚÏ, Ð ÊĐ ² ÚÏ ; ««Ð ÊÒ ¼Î ¼Ò Ä Ò ÚĐ, Ï. Ú [15,16] ²Ö, ± Ä Co ZnO ¼ÎÒÏ ÇÇ Ò Ç; ±» ± Co ZnO ¼ÎÒÏ [17,18]. Ï ¼ÎÒÏ, ¼Î ÒÏ ÃÇ, ÐÓÎ Ò, ¼Î ² ÈÉ Ï ¹ ÐÓÒ µ, ¹ ÐÓÈ Ç ÏĐ Ú. ¾«, Ü ÇÌ Đ Ú Ò ÇÌ Ê. Ì ¹ Co ZnO ¼ÎÒÏ, µ¼îò Ï»Þ, ÒÏ, ¹¾ Ð Ð Ì 5 ¹ ÏÒ Zn 1 x Co x O Ò Þ, Ä Ú Ì Co ÒÙ Ä ¼Î Ï Ò Ç. 1»«Å Zn 1 x Co x O(x=0.01, 0.02, 0.03, 0.04, 0.05, ) Â Ò Ã ³ ÉÎ Ì 99.99% Ò Ù Å Ý (Zn(CH 3 CO) 2H 2 O) Ä Û Ù Å Ý (Co(CH 3 CO) 4H 2 O), µý Å 0.8 mol/l ½Ù ÅË. Ö 1.6 mol/l ÒÅË«Ú»ÞÐ, Î 60 Ù², È 2 h. Ý Ê Ò Ð Î 48 h Î, Ù Ð± ÊÒ Þ Å Ò Í Ð. ÝÍ ÐÖ Ì 220, À ² Ð, Ý² Ð ÅËÄº Ù À² ÚÛ Þ. ÉÒ Þ ³, ³ 500, 600, 700, 800, 900 Ä 950, Ï 2 h. Ì, ÝĐ S x,t À, x ² É, T ² Ð ( ). Đ Ò ³¾ X ÀÁÜÀ (XRD, CuK α, X pert High Scoreplus) Ä H 600 ÀÜ (TEM) Ù Ä ; Đ Ò Ä JCM 5400 ÔÜ (SEM) Ä (EDS) ²Â; Đ ÒÏ Lake shore Cryotronic 736 ÐĐ Ï Ò (VSM). 2» 2.1 XRD Ì½ ZnO Co Ò, Å Ò Ç, Â XRD Đ Đ Ì²Â. 1a 2θ=25 70 ÜÀ, S x,500 ÞÒ XRD, S 0,500 ² Ò ZnO ÞÒ ÜÀ. «¼È, Đ Đ, ±² Co Co ÐÎ Ô ÂÒÜÀ. Ì ¹Ã Co ZnO Òµ, 1a Ì º (2θ=31 37 ), 1b Đ. ² Ò ZnO Â, Co ÒĐ ºÜÀ µ ÇÌ, ²Ö Ð. ¼², Ú ÜÒ Co ZnO 2 Ò : ÄÅµ. Co 2+ Ò ( nm) Zn 2+ Ò ( nm), Co «ZnO, Þ Ò ; «Åµ Ð., Ú Ò Co Ç «Åµ ZnO. Ð, ºĐ Ò XRD 1

3 3 ³ ÛÓ : ß ßÆÏ Ð Zn 1 xco xo ÜÐ ÂÍ S 0.04, 500 S 0.03, 500 S 0.02, 500 S 0.01, 500 S 0, S 0.05, 950 S 0.05, 900 S 0.05, 800 S 0.05, 700 S 0.05, S 0.04, 500 S 0.03, 500 S 0.02, 500 S 0.01, 500 S 0, S 0.05, 950 S 0.05, 900 S 0.05, 800 S 0.05, 700 S 0.05, S x,500 (x=0, 0.01, 0.02, 0.03, 0.04, 0.05) Ý Ñ XRD Fig.1 XRD spectra of S x,500 (x=0, 0.01, 0.02, 0.03, 0.04, 0.05) powders 25 2θ θ 37 Â Ò. 2 Co ÉØ Ò S 0.05,T ÞĐ Ð Ò XRD. 2a Đ, Ð µ 950, S 0.05,950 ¾ Á ZnO, Ø ÂÜÀ È. 2b 2a Ò º (2θ=31 37 ), Ð Ï, ÜÀ Ò µ ß Ð Ò µö, Scherrer equation ÒÞ ²Ö Å, É µ; , µ Ò Î Ö, Å Î. Ï, ÜÀ Ò µ Ð Ð Ò Ç, Ð , Ì Ö ; , Ö. ²Ö Co Â Ï, ÒÐ ÐÒ. Đ Ò XRD È ZnO Ò ÜÀ, Ø Â. Ä Å ßÐ Ò Î Á 3 Đ. «¼È, ßÐ Èµ, Û Ê ; Å ß Ð ÒÈµ ÊÛ, « Ù. Đ Ò Ä Å Ð Co ÄÐ ÒØ Ç S 0.05,T Ý (T=500, 600, 700, 800, 900, 950 ) Ñ XRD Fig.2 XRD spectra of S 0.05,T (T=500, 600, 700, 800, 900, 950 ) powders 25 2θ θ 37 XRD ²Ö Đ Đ «É Ò Co ÐÎ Ò,, µ XRD ÒÙ Ò, Ã : (1)Co ÐÎ «Ò ; (2)Co ÐÎ «ÉÒ ; (3)Co Ç Ì, ¼ Co., ¾ TEM, SEM Ä EDS. 2.2 TEM, SEM EDS 4 S 0.05,700 ÞĐ Ò ÀÜ ÜÀÌĐ. ÌĐ Ú Å ÜÀÌĐ, µ Â ÒÜÀ È. ¹ ZnO ÒÜ ÜÀ, «± TEM Ò XRD ºÆÇ,, «É Ò Co ÐÎ «Ø ÂÒ. 5a S 0.05,700 ÞĐ Ò SEM Ê. «¼ È, Đ Å, Å É» 100 nm. Â Scherrer equation ÒÞÒ Å (32 66 nm) Â Ç, ¹ Å Å¹ Å, ÅÈ Ó ± Í Ç, Í ÆÏ Å ÂË Ò Â. 5b S 0.05,700 ÞĐ Ò EDS. Si Ä C Ð, Đ Ò Co (Zn+Co)=

340 Ó Ô 47 0.3252 0.3250 a, nm 0.3248 0.3246 0.3244 0.3242 0.3240 0.5208 0.5206 0.5204 S 0.01, T S 0.02, T S 0.03, T S 0.04, T S 0.

5196 500 600 700 800 900 1000 T, o C 70 (c) 60 Grain size, nm 50 40 500 600 700 800 900 1000 T, o C 3 Ö a, c Ã Ä Ñ Fig.

«¼È, Đ Ö ÒÏ Í. Ì Ð ÏÎ Ò Ç, 7»ÈÌ Ð S 0.01,T ÞĐ ÒÏ Á. 7a Ï ¹ 10 4 Gs H 10 4 Gs Ï S 0.01,T ÞĐ ÒÏ Á. «¼È, S 0.01,700 Ò ÄÏÎ M s Ø, ÏÚÑ M s (S 0.01,600 )< M s (S 0.

4 340 Ó Ô a, nm S 0.01, T S 0.02, T S 0.03, T S 0.04, T S 0.05, T T, o C c, nm S 0.05,700 Ý Ñ Û Û É Fig.4 The SAED pattern of S 0.05,700 powder T, o C 70 (c) 60 Grain size, nm T, o C 3 Ö a, c Ã Ä Ñ Fig.3 Relationships of a, c and size of crystal grain (c) with the sintered temperature 1 ( ), Đ ÒÙ x=0.05 ÆÇ. 2.3 VSM Â VSM Đ Đ Ì Ï ²Â. 6 Đ Đ ÄÏÎ Ø Ò S 0.01,500 ÞĐ ÒÏ Á. «¼È, Đ Ö ÒÏ Í. Ì Ð ÏÎ Ò Ç, 7»ÈÌ Ð S 0.01,T ÞĐ ÒÏ Á. 7a Ï ¹ 10 4 Gs H 10 4 Gs Ï S 0.01,T ÞĐ ÒÏ Á. «¼È, S 0.01,700 Ò ÄÏÎ M s Ø, ÏÚÑ M s (S 0.01,600 )< M s (S 0.01,500 )< M s (S 0.01,900 )< M s (S 0.01,950 ) < M s (S 0.01,800 )< M s 5 S 0.05,700 Ñ SEM ÉÃ EDS Fig.5 SEM image and EDS result of S 0.05,700 powder (S 0.01,700 ). Ý 7a Ò Ï ¹ 10 3 Gs H 10 3 Gs º, 7b Đ. «, S 0.01,600 Ò M s Ø, Ç H c, ÊÏ M r /M s ÄÏ BH Ø., S 0.01,T ÞĐ Ï Ø ÒĐ S 0.01,600, S 0.01,700. Ì Co Đ Ï Ò Ç, 8»ÈÌ S x,700 ÞĐ ÒÏ Á. 8a

5 3 ³ ÛÓ : ß ßÆÏ Ð Zn 1 xco xo ÜÐ ÂÍ M, Am 2 /Kg S 0.01, 700 S 0.02, 700 S 0.03, 700 S 0.04, 700 S 0.05, S 0.01,500 Ý ÑÎ À Fig.6 The magnetic hysteresis loop of S 0.01,500 powder at room temperature S 0.01, 500 S 0.01, 600 S 0.01, 700 S 0.01, 800 S 0.01, 900 S 0.01, H, Gs 8 S x,700 (x=0.01, 0.02, 0.03, 0.04, 0.05) Ý ÑÎ À Fig.8 Magnetic hysteresis loops of S x,700 (x=0.01, 0.02, 0.03, 0.04, 0.05) powders at room temperature 10 4 Gs H 10 4 Gs 10 3 Gs H 10 3 Gs H c (S 0.04,700 )< H c (S 0.01,700 ) < H c (S 0.02,700 ), «M r /M s Ä BH Ò ÏÚÑ ³ : M r /M s (S 0.05,700 )< S 0.01,T (T=500, 600, 700, 800, 900, 950 ) Ý ÑÎ À Fig.7 Magnetic hysteresis loops of S 0.01,T (T=500, 600, 700, 800, 900, 950 ) powders at room temperature 10 4 Gs H 10 4 Gs 10 3 Gs H 10 3 Gs Ï ¹ 10 4 Gs H 10 4 Gs Ï S x,700 ÞĐ Đ ÒÏ Á. «, ¼µ, ÄÏ Î ¼. ÄÏÎ µ Ä, ÏÚÑ : M s (S 0.01,700 )< M s (S 0.02,700 )< M s (S 0.03,700 )< M s (S 0.05,700 )< M s (S 0.04,700 ). 8b 8a Ò º, Ï ¹ 10 3 Gs H 10 3 Gs. «¼È, H c Ò ÏÚÑ : H c (S 0.05,700 )< H c (S 0.03,700 )< M r /M s (S 0.04,700 )< M r /M s (S 0.03,700 )< M r /M s (S 0.01,700 )< M r /M s (S 0.02,700 ) BH(S 0.05,700 )< BH(S 0.04,700 )< BH(S 0.03,700 )< BH(S 0.01,700 ) < BH(S 0.02,700 ). 3 ± ¼² XRD Ä TEM Ò Ò²Â, Co Ò ZnO, Ì Ò ZnO Â, Co ÐÎ Ò Â, Ò Í. «EDS ²ÖĐ ½ Ù ÉÂ Ò Co., «Ç¹½Þ Co «¹ Zn Ò Ì., Ú Co Ò Õ, ÉÐ Ù Đ Ù Ò Co ÐÎ., ÀÌ Òµ ( 400 ) Ð, Co 2 O 3 Ä Co Ò Ç ; Ç Ò CoO [19,20] Ä Ò Co ÐÎ [21 24], ±, Co ÐÎ»Þ [19,21], Ï Ò, Øµ Neel 298 K [22,25],, «Đ Ò Ï Ð Â, «ÂÕ. Co 2+ Đ ¾ÒÜ ÐÓ

6 342 Ó Ô 47 Ò, «± ; ÏĐ Ú Ò, «É Ò. Đ Ú ÒÐ ¼, ÝĐ ÒÏ È. 7 Ç, S 0.01,T ÞĐ, S 0.01,600 Ò Ï Ø, S 0.01,700 È; ¼² 3a Ä b ¾Ò ²ÒÞ V cell (S 0.01,600 )= nm 3, V cell (S 0.01,700 )= nm 3, ³ Ï Ø Ä Ò. Co Â Åµ Ò Ü, V cell Ò Î ZnO Â» Ò»Þ [12] ; Å ¹ [12] Ò, Ð, Â» Zn (Zn i ) Ä O µ (O v ) Ò Ç Ò Î; S 0.01,600 S 0.01,T ÞĐ V cell Ø, Æ³ Zn i Ø O v Ø, Ø. Zn i Ä O v ¾ ±ÎÒ n. ±Ü Ã Ì Ï ÏĐ Ú ÒÐ, Ì Ò. Þ O v Ì Zn 1 x Co x O ¼Î Ò Ï Đ Ú [10] ÒÒÞ ÂºÆ. «: S 0.01,600 S 0.01,T ÞĐ V cell Ø, O v Øµ, Đ«Ï Đ Ú Ø ; S 0.01,700 Ò V cell, Ï. ÞĐ ÒÏ ĐÆ. Ç., Å (S grain ) Đ ÒÏ ÇÌ, S grain Ä V cell ÇÌĐ ÒÏ, µ Å Ò ¼Å, V grain /V cell ¼, ¼ Â ÏÑÒ. 3c Đ, S 0.02,700 Ò S grain S x,700 ÞĐ Ø. Ý Å, ÒÞ È V grain /V cell (S 0.02,700 )= ¹, Đ, Đ«S 0.02,700 Ò H c, M r /M s Ä BH S x,700 ÞĐ Ø. V grain /V cell Ò ÏÚÑ : V grain /V cell (S 0.05,700 )< V grain /V cell (S 0.04,700 ) < V grain /V cell (S 0.03,700 )< V grain /V cell (S 0.01,700 )< V grain /V cell (S 0.02,700 ); ÉÌ M s, Ï H c, M r /M s Ä BH Ò ÑÄ ÈÂ, 8b Đ. Đ«, «ÅÖ ÌÐÓÒ Ì Ï. ¾, ÞÒÏ (x) ÆĐ Ï Ò Ü. S 0.02,700 ÞĐ Ò H c, M r /M s Ä BH S x,700 ÞĐ Ø, x Õ, M s (S 0.02,700 ) ¾ M s (S 0.03,T ), M s (S 0.04,T ) Ä M s (S 0.05,T ). Ñ, x Õ, ¼Î ÐÓ Ò, «Ï Ñ; Ö x «ÖĐ ÒÐÓÒ, Đ Ï Ò µ x Ä., x µ, O v Ô, ÏĐ Ò ÃÇ, «Ö O Ò ÏĐ Ò, Î ¼ÎÒÏ. Đ«, Þ Ò O v, ½ ÆÐÓÈ Ç Ï Đ ;, Å µ Ö ÏÑ. Đ«, µ x Þ µ M s., Ì µ x ± ¼ÎÒ Ï ÂÒ, µ O v ± É, ¼ÎÒ Ï ½ ±. 4 (1) Ð Ð Ò Zn 1 x Co x O Ò Þ, XRD Ä TEM Ù Ä Ò Co Co ÒÐÎ, Đ Đ ÁÌ ZnO Ò, Ê º¹ÜÀ Ò. ²Ö Ò Co 2+ «Åµ ¹ Ì Ò Zn 2+. (2) Zn 1 x Co x O Ò ÞĐ Ï, Ï Zn 1 x Co x O Ò ÂÕ. (3) Đ ÒÏ Co, Đ Ò. Ï, O v ÃÔ, Å Ô Â ÏÑÒ. Đ º Ï Ø Ò ³ H c (S 0.02,500 )= Gs; M r /M s (S 0.02,700 )=0.1813; BH(S 0.04,950 )= J/kg; M s (S 0.04,950 )= Am 2 /kg. [1] Shen W, Wang J, Duan Y, Wang Q, Zeng Y P. J Semicond, 2005; 11: 2069 [2] Wang X D, Song J H, Jung H J. Science, 2007; 316: 102 [3] Jin Z W, Fukumura T, Kawasaki M. Appl Phys Lett, 2001; 78: 3824 [4] Dietl T, Ohno H, Mstukura F, Cibert J, Ferrand D. Science, 2000; 287: 1019 [5] Zheng R K, Liu H, Zhang X X, Roy V A L, Djurišiæ A B. Appl Phys Lett, 2004; 85: 2589 [6] Lawes G, Risbud A S, Ramirez A P, Seshadri R. Phys Rev, 2005; 71B: [7] Park J H, Kim M G, Jang H M, Sangwoo R, Kim M Y. Appl Phys Lett, 2004; 84: 1338 [8] Yan G Q, Xie K X, Mo Z R, Lu Z L, Zou W Q, Wang S, Yue F J, Wu D, Zhang F M, Du Y W. Acta Phys Sin, 2009; 58: 1237 (Ù ³,»Ò, ß,, Ó ², Â, ¾ µ, ¾ Đ,, Đ. Ö, 2009; 58: 1237) [9] Wang Y, Sun L, Han D D, Liu L F, Kang J F, Liu X Y, Zhang X, Han R Q. Acta Phys Sin, 2006; 55: 6651 ( Ý,,, Æ, ½, ÏÝ,, Þ. Ö, 2006; 55: 6651) [10] Chen J, Jin G J, Ma Y Q. Acta Phys Sin, 2009; 58: 2707 (, Æ º,. Ö, 2009; 58: 2707) [11] Chamber S, Vuthasans T, Farrowr F. App Phys Lett, 2001; 79: 3467 [12] Cheng X W, Li X, Gao Y L, Yu Z, Long X, Liu Y. Acta Phys Sin, 2009; 58: 2018 (, Ã, ¹,, Ø,. Ö, 2009; 58: 2018) [13] Céspedes E, Castro G R, Jiménez Villacorta F, Andrés A,

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