V N IJ Joimial ofvScicncc, M athem atics - Physics 25 (2009) 199-205 Signficantly improving magnetic properties o f Sr-La-Co hexagonal ferrite N g u y e n K h a n h D u n g ' * N g u y e n T h i L e H u yen " ' V/oC/i/A/Z/i/; O n ' University o/ỉtHỈitsỉry Ỉ2 Ni^uycn Van Bao, Ward Go Vap District, ỉĩochim inh city, Vietnam Institute o f Physics in ỉỉoC hiM inh City Ỉ M ac Dinh Chi, I District, Hochiminh city, Vietnam Rcceivcd S eptem ber 2009 A b s t r a c t : 'Ỉ he liard inamielic fcn ite system o f S rj.xLaxl'ei 2-vCoyOi with X ^ 0.04).3 and y = 0.00.3 has been prepared bv tratlilional ccramic tcchnolouy and show ed hexagonal crysĩalline siruclure o f M - Ỉ \ p c 'he anisotropic sample Sro.gLao^Fci 17C00.3O19 % weight SÌO2 sintered al ì2 '’C/2h has llic best hard magnetic piopcrlies, nam ely Bf = 4.66 kG; bH c = 3.46 kO e and ~ 5.70 M G O c I'he role o f La and Co as well as the reasons leading to these perfect propei tics o f the studied ferrites have been discusscd based on llie overall studies o f structure and chdiaclcristics o fc x a n iin c d samples Ỉ Introdu ction In more than a h alf century from the discovery o f hexagonal fcưite, ferrite magnets always used very popular and evcrvvvhcrc in scicncc tcchnoloịzv life and especially in civil electronics industry, in com m unications and other diffcrcnl areas due to chcap price as well as simple technology But still now Ihc problem to i m p r o v e hard magnetic properties ỊÍ’ this kind o f materials always attracted the rcscaichcrs and tcchnolouists VVc arc talking about two main rollowm g trends: - Using diỉTcrcní doping elem ents including 3d and Rarc-carth metal oxides with hoping that s a tu r a tio n niag ncti/ation and magnctocrystallinc anisotropy will be im proved [1-4J - Applying advancc technologies such as coprccipitation, sol-gcl, high pressure com pressing, hot p re s s in g , isostalic prcssiim to m anufacture le m tc pow der and product Ị - ] In this report \vc study the struclurc and magnetic properties o f icrritc system Sr,.xI^axI'ei 2_yCOyO|9 (x = 0 -0 and y = 0 -0 3) to improve the quality o f hard m agnetic ferrite and explain the reasons leading to these results E xperim ent Substitution in our study was the simultaneous doping o f La and C o in system Sri.xLaxFci^.y CoyO|ọ + 0.5% weight o f SiOi Raw materials used here arc SrCOj, FC2O , La 2Ơ , C oO and SiO with Corresponding author F-mail: nkdung2009@ yalioo.com 199 200 N.K Dunẹ, N J '.L ỉ ỉ u y e n / \'N U Jo u rn a l o fS c w n c c M athem atics - P hysics 25 (2009j Ỉ 99-205 high purity (3 - N) Wet planetar) ball mill lias been used lo proxidc line ỊK)udci with main si/C around IỊ.II1Ì riic ratio between powder: ball; water was 1:4: I We kept the moisture o f p o u d c r about 35% for anisotropic pressing To orientate the particles along the m agnetic field, the field strength o f !T and llic pressure OÍ' 500 kG/c'iii have been applied Tlic samples were sintered at temperatures 1260‘’C !27()"C, 1280''c and keeping lime was 2h A pproxiniatelv, the clicmical coniỊX)silion o f samples was checked bv lEDS iacilily The thermal transitions w ere pcrfoniiL'd by D ['A - D'l'G machine, [ lie crystallographic struclure o f samples was exam ined by X-ray dirfractoniclci (Siemens D5005 X-ray, G erm any) M icroslriicture o f isotropic and anisotropic sam ples has been studied usinu SHM (J li0 l.-J S M L V , Japan) Magnetic properties are invcslii^atcd by V SM (200C Nini, USA), hystcrcsisgraph (A M H 0-20 , U SA ) and m agnctomclcr using high pulse nuii^nctic n d d to measure SPD curve R esults and discussion Fig shows dem agnetizing curves o f Sr-La-Co anisotropic sam ples s i n t e r e d at 1280‘'C/2h T h e main characteristics derived from this figure are presented in Table Table The main hard m agnetic parameters o f anisotropic sam ples sintcrd at 1280"C72h Sample C o m po un d Ml M2 M3 M4 Sr!-'ei: } Srygi-a(i2Ỉ'Ci20Ị9 Sro Lao Í‘C|Ị yCoo )Oi Sro gLa stall me anisotropy and normally plays a dccidcd role for creating high cocrcivity o f m a t e r i a l s I'or this reason alm ost authors focusing to find the way for increasing K | o f hexagonal ferrite mainly by substitution effects The sccond term in (1) dealing with shape anisotropy o f particles Íoriiiiiìíi material and takes part o f several tens percent o f He and finally the last term in ( ) determined by Iiiagnctic elastic energv and oflcn is small and could be ignored Apart from above iiidicalion the general orientation to improve hard m agnetic properties o f hexagonal ferrite is to make raise niaunclocr>'stallinc anisotropy, shape anisotropy o f particles as well as saturation magnetization Constant Ki w as m easured in m agnetom eter with hiuh pulse m agnetic field using special point dcicction (SIM)) tcchnicque I'ig.2 show s the m easurements o f M (H ) curvc and d M/ d li (H) curvc for sam p le M so 70 60 5(» puralie 4U M) 2U / iO \\ » pcrpcndicular ' ^1 II (T) I II(T) curve (right) o f sam ple M4 sintered at 1260‘’c/2h Fig M (II) curve (left) and ^ J//' able Cotìstaiiỉ Ki o f sam ples M i and M4 derivci Irom SIM) m easurem ent ■Sample Ml K ị XỈÍ? [J 'm' 3.60 M4 3.93 T abic l.altice param eters o f studied Sri aTo-M ferrites SampLMl M3 M4 lA i 5.8868 5.8775 5.8740 lA i 23.0370 23.1034 23.1091 N'casurcd results from T a b showed the value Ki = 3.6.10^ J/m^ for pure SrM ferrite which is comp etcly agreem ent with the results given by other authors, for exam ple [5, 10, 11 ] Note that ferrite Lal-C has K ,= ( Ỉ - Ỉ ) 10' J/m^ at OK [12], whereas ferrite C o F c has Ki = 3.9.10^ J/m^ at room temperature [13] n Zijistra [14] pointed out that in La-Co ferrite anisotropic field lla could reachtlic value o f lO^A/m and Ki = 5.10^J/m \ T h i s with llie sim ultaneous substitution o f La for Sr and Co for Fe in the SrM-ferrite hard magnetic properties o f hexagonal ferrite significantly improved T ic crystallographic structure o f samples has been exam ined by diffractom eter and the X RD p a ltc n s o f samples M l, M and M are presented in Fig.3 The results indicated that the structure o f studied ferrite corresponding lo m agnetoplum bile structure with c-axis is a little longer but a-axis is shrinlcd a little in com parison with pure SrM-fcrrite as shown in T ab.3 202 V-A', Dunị^, N T L ỉĩu y e n ■ \'N V Jo u rn a l o f Science M athem atics - Pỉiysics 25 (2009) ỈỌ9-205 Ml S iO F ea0 a ci u c M4 M3 Ml 20 Fig X -ray diffraction patterns o f the samples M I, M3 and M4 sintered at 1260‘’C/2h From T ab.3 we can conclude that by substitution in our study the unit lattice has m ore shape anisotropy wilh longer needle form To understand about particle size o f fine milled SrLaCo-fcrrite, the pow der vsas m easured by Microtrac machine S3000 and ihe results are indicated in 7'ab.4 It is clearly seen that in sam ples M |M almost the particles have small size and especially by optimal substitution in sample M , 100% of particles has single dom ain structure with high shape anisotropy (Tabs and 4) Table Crystal grain size o f SrLaCo- ferrite, which was presintered and fine milled Sample Crystal grain size [urn] (ratio) Ml 33.69 (5% ) 1.55 (54% ) ( % ) M2 30.93 (3%) 1.62 (54%) 0.39 (43% ) M3 26.33 (7% ) 1.69 (58” o) 0.41 (35% ) M4 1,59 (46"i,) 0.37 (5 4% ) Figs and show the SEM pictures o f the samples From both figures we can sec the iiiiliicncc OÍ substitution to make finer and more homogeneity o f particlcs which arc correspond to siniile domain structure It is also obviously seen from Fig that the appropriate substitution (and small dopinu o f SÌO ) nol only restricting the grain grovvth but m aking the m ore shape anisotropy o f them and both these factors leading to enhance the hard magnetic properties o f studied samples O ur purpose is not only to achieve high He but also lo reach high value o f magncti/.ation I'o llnd the solution for this problem, alm ost the authors focusing on the w ay to make increase Iip-spin o f positions 2a and 2b A bout the role o f La to improve hard m agnetic properties o f hexagonal ferrite, the V ietnamese researchers have published a large num ber o f publications am on g them several has been occured on the International Journals [15 -18] In order to understand and discuss on the advance o f La and La-Co as well as applied leclinology o f authors inside and outside V ietnam we derive here some main related results: In previous our work [14], the structure and magnetic properties o f ferrite (SrO)i.v(La: )^n , (Fc ) + 0.5% weight SÌO (x = 0.00 to 0.12) have been detailly investigated, riic new icchnology was applied there, nam ely the wet isostatic pressing was perform ed in a rubber die pressing Í3y that tool we have succeded to prepare anisotropic samples with very high density (d> 99 % dx ) and ver\ high orientation degree o f particles along magnetizing fiek' applied in pressing process and \vc have N Ả D ung N T.L H uyen / V N U J o u rn a i o f Science, M athem atics - P hysics 25 (2009) Ỉ 99-205 203 rcccivcci icrritc sam ple with rccord quality for quite long time: Br = 4.3 kG; nHc = 3.2 kOe, (BH), 5.5 M Q X )c) Fig SEM Images of anisotropic bulk samples MĨ, M4 perpendicular (left) and parallen (rigth) to the preferred magnetizing direction (bright line is |im) l-iii sr.M Imaiics of isotropic bulk samples Ml siiitcrcd at Ỉ260‘’c/2h (bright line is li is well know n lhai the ions which are origine o f m agnetic m om ent o f hexagonal ferrite noniiall} localcd at 2a, 2b and 12k positions (up-spin) and 4fi and 4Ỉ2 positions (down-spin) in the crystallo^rapllic lattice Therefore magnetic mom ent o f a m olecule Sr F ei is equal lo 20|ÌB The substilution o f l.a for Sr leads to the following change: s r " + hV* La S fV * ( 2) i Hie peribrm cd ions possibly are located at 4fi and 4Ỉ2 positions (dow n-spin) and because ion ! c has siiiallcr magnetic m om ent than o f ion this valency conversion led to the increase o f total n ia u iic ti/a lio ii o f fe rrite - Sc-Dong Yang ct al [ 19 ] studied two compositions S rFcii 7C003O19 and Sro7l-ao3Fcn C003O19 iuid showed that Co alone enhanced Br but both La and Co im proved He- R Cirossinger ct al [20] indicated that the sim ultaneous replacem ent o f La and Co in SrM Ic rrilc Iioiably i n c r e a s e d l i e d u e to in c r e a s i n g o f a n i s o t r o p i c field Ha a n d e s p e c i a l l y th e y a l s o h e lp e d stabiỉi/c i !(, on tem perature but one ncccssar>' thing is the replacem ent fractions arc not exceeded 0.25 mol - K Masuzawa ct al [2 ] have studied ferrites Sri.xLaxFeii 7C003O19 and showed that with X = 0.3-0.4 ferrites have phase M W hen X 0.4 magnetic properties o f ferrite strongly decreased, particularly for the remanent induction Bj bccausc o f occurring hem atite phase - Y Kubota et al [2] exam ined ferrite system (Sr^^ x)0 n{(Fe^''i yCo^'‘y)2 } w here X = 2ny and n = 5.4-6.0 and showed that by substitutions o f La for Sr and C o for Fe, respectively, jHc o f ferrite is significantly increased while Br only slightly enlianced (jHc - 4.5kO e; Bj = 4.4kG) The 204 N.K Díỉiĩg N.T.L Ịỉu y c n / \'N U Jo u rn a l o f Science M iiihem atics - P hysics 25 Ỉ2009) Ị 99-205 authors explained that ihc residual orbital magnetic m om ent o r i o n plays the main lolc to make high value o f He- F Kools ct al [22] studied fcm te system Sr].J.aJ*'C| 2.^CoxC)i9pc Hcxa-Fcrntcs Proc o f ỉfu' ICỈ-V, SanF-rancisco, California, USA (2004) 573, [5] E.Oda; Preparation ofSr-Fcrritc powder by pyrolysis Tcchniquc, Digests o f the ICFH, Kyoto, Japan (2000) [6] S.R Janasi, cl al Barium Ferrites powder obtained by Coprccipitation, Digests o f the ỉ c r s , Kyoto, Japan (2000) [7] M Sagawa, ct al Rubber isostatic Prcssinc for Fcrntc Magnets, J Phys /K, Franco (1997) C l 307 [8] [9] 363, T Kikuchi, cl al Magnetic Properties of La-Co substituted M-Typc Sr-Fcrritc ukrafinc Powders prepared from C i t r a t e rccursors /Voc o f the ỈCF9, SanFrancisco, California, USA (2004) 75 L Nccl Magnetic Properties of Ferrites: Fcrrimugnctism and Antifcrromagnctism, Ann Phys (Pans) (1948) 13" [10] H, Kojima, Fundamcnlal Properties of hexagonal Fcrntcs wiih magnctoplunbitc Structure, h'erronuignctu' M uttnaỉs (Edit By EV Wohifarth), Voi.3 (1982) 305, [1 1] L Jahn, II.G Muilcr The Coccivity of hard Ferrite single Crystals, Hiys Sialus Soiiíỉ 35 (1969)723 [12] F.K Lotgcrtng, Magnetic anisotropy and saturation of LaFcl2019 and some related Compounds, Phys Chent S)ỉịJs 35 (1974) 1631 N.K- Duỉiịĩ, N T.L ỊỊuyen / VN U J o u rn a l o f Science, M athem atics - P hysics 25 (2009) 199-205 205 ịl | J Sniit, Í1 f* J Wijn, Ferrites - Physical Properties of fcrrimagnctic Oxides in relation to their technical Applications, P h ilip s ' ic c h n ic a ỉ L ib r a r y E tn d h o v c ti 1959 [14| II, /ijlstra, f*crmancnt Mauncis: '1‘hcory, Fcrromagn, Materials (Kdit By E.p Wohlfarth), North !ỉoỉỉand Publishing Comp \'ol (1982)37 |15| N C'hau, N.K Dung, [).L Minh, B.T Cong, On the nature of high performance hard magnetic propclics of Sr-Fcrrite ỉ.a doping, Diị^esis o f the ICFS, K yoto, Japan (2000) 13 116) N.K Dune D.L.Minh, B.T.Cong, N.Chau, N.X.Phuc, The influcncc of La203 substitution on the structure and properties o f Sr f c m tc , J Phys l y , Francc (1997) Cl i3 |!7] N Chau, N.K Dung, D.L.Minh, n.T.Cong, High hard magnetic properties of Sr hexagonal ferrite substituted by La, Proccaỉiỉigs o f the International Meeting on Frontiers o f i^ 's ic s , Kuala Lumpur, Malaysia, October 25-29 (1998) 170 [IS) P Q Nicm N Chau, N.H.Luong, D-L.Minh, Influence of La doping on the properties of Sr-Ba hexagonal ferrite, rh y sica HỈ { H m ) 266 [19] Se-[)ong Jang, Cl al A Study on Substitution of Elements for Strotium Ferrite, Digests o f the ICF8, Kyoto, Japan (2 0 ) [20] R (jrossiniicr, ct al Anisotropy and Cocrcivily of M-Typc Ba and Sr- Ferrites containing La and Co, Digests o f the ICFH, Kyoio, Japan (2Ơ00) | 11 K Masu/awa.ct al Maunctic Properties of Srl-xl.axFel 1.7Co0.3019 anisotropic Magnets, Digests o f the ICF8 Kyoto, Japan(2000) 10 [22] F Kools, Cl al LaCo substituted Sr and Ba M-TypcFerriics; Magnet Properties versus intrinsic and microstructural [■'actors, D ii:csis o f ihc ICFiS, K yoto, Japan (2000) 12 ... 11 ] Note that ferrite Lal-C has K ,= ( Ỉ - Ỉ ) 10' J/m^ at OK [12], whereas ferrite C o F c has Ki = 3.9.10^ J/m^ at room temperature [13] n Zijistra [14] pointed out that in La-Co ferrite anisotropic... Obara, ct al Magnetic Properties of Sr-La-Co M-Typc f'crritc fine particlcs, DiịỉCỉiís o f the K'FH, Kyoto, Japan ( 2000 ) [4] M Ỉ.C Breton, ct a! Intrinsic and magnetic Properties of La-Co substituted... California, USA (2004) 75 L Nccl Magnetic Properties of Ferrites: Fcrrimugnctism and Antifcrromagnctism, Ann Phys (Pans) (1948) 13" [10] H, Kojima, Fundamcnlal Properties of hexagonal Fcrntcs wiih magnctoplunbitc