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EVIDENCE OF MANY CHARACTERISTIC TEMPERATURES IN LiTiZn FERRITES WITH
TITANIUM CONTENT
G. Nicoara, M. Guillot
To cite this version:
G. Nicoara, M. Guillot. EVIDENCE OF MANY CHARACTERISTIC TEMPERATURES IN LiTiZn
FERRITES WITH TITANIUM CONTENT. Journal de Physique Colloques, 1985, 46 (C6), pp.C6-
437-C6-440. �10.1051/jphyscol:1985684�. �jpa-00224946�
JOURNAL DE PHYSIQUE
Colloque C6, supp16ment au n09, Tome 46, septembre 1985 page C6-437
EVIDENCE O F MANY CHARACTERISTIC TEMPERATURES I N L i T i Z n FERRITES WITH TITANIUM CONTENT
G. Nicoara and M. ~ u i l l o t '
Institute of Physics and Technology of Materials, P.O. Box Mg-7, Bucharest-Mangurele, Romania
+~aboratoire Louis Ne'eZ, CURS-USMG, 166 X, 38042 GrenobZe Cedex, France R6sum6
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L16tude d e s p r o p r i 6 t b s magnetiques des f e r r i t e s s p i n e l l e s LiTiZn B h a u t t a u x de t i t a n e met e n Bvidence 4 tempdratures c a r a c t d r i s t i q u e s : l a temperature de Curie (Tc) r e s t e c o n s t a n t e malgr6 l a d6croissance de l a c o n c e n t r a t i o n e n ~ e 3 ' ; a u dessous de Tc, il e x i s t e un brusque changement d e s p r o p r i 6 t 6 s magnbtiques do ?I l l a p p a r i t i o n d l u n e s t r u c t u r e a n g u l a i r e . Au-dessous de Tc, il e x i s t e deux a u t r e s temperatures c a r a c t b r i s t i q u e s , l l u n e d l e n t r e e l l e s est a s s o c i b e ?I l a t r a n s i t i o n c r i s t a l l o g r a p h i q u e o r d r e - d6sordre du s i t e o c t a 6 d r i q u e . L ' i n f l u e n c e de l a temperature de trempe s u r c e s d i f f e r e n t e s p r o p r i b t 6 s e s t 6tudi6e.A b s t r a c t
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The magnetic p r o p e r t i e s o f LiTiZn s p i n e l s f e r r i t e s w i t h h i g h t i t a n i u m s u b s t i t u t i o n a r e r e p o r t e d ; f o u r c h a r a c t e r i s t i c t e m p e r a t u r e s a r e observed ; t h e Curie temperature which remains p r a c t i c a l l y c o n s t a n t a l t h o u g h t h e d e c r e a s i n g o f t h e ~ e 3 + c o n t e n t ; below Tc it a p p e a r s a change of t h e magnetic behaviour a s s o c i a t e d t o t h e o n s e t of non c o l l i n e a r s t r u c t u r e ; above T,, two c h a r a c t e r i s t i c temperatures a r e observed, one of them o r i g i n a t e s from t h e c r y s t a l l o g r a p h i c o r d e r - d i s o r d e r t r a n s i t i o n . The i n f l u e n c e of t h e quenching temperature is presented.I
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INTRODUCTIONThe f e r r i m a g n e t i c Li-Ti-Zn systems have p o t e n t i a l a p p l i c a t i o n i n microwaves d e v i c e s because of t h e i r r e c t a n g u l a r h y s t e r e s i s loop, h i g h Curie temperature, narrow e f f e c t i v e l i n e w i t h and low c o s t .
They a r e d e r i v e d from t h e pure l i t h i u m f e r r i t e L i 0 . ~ F e 2 , 5 . 0 ~ which p r e s e n t s two c r y s t a l l o g r a p h i c phases ; each of them coresponds t o e i g h t molecules per u n i t C e l l / I / . The d i s o r d e r e d Li0.5Fe2.504 is an i n v e r s e s p i n e l w i t h t h e space group Fd3m ;
t h e t e t r a h e d r a l (A) s i t e s ( 8 a ) a r e occupied by e i g h t Fe atoms o n l y ; t h e f o u r L i and t h e twelve remaining Fe atoms a r e s t a t i s t i c a l l y d i s t r i b u t e d over t h e o c t a h e d r a l ( 9 ) sites of t h e s t r u c t u r e (166). The o r d e r e d phase is c l o s e from a n i n v e r s e s p i n e l ; t h e s p a c e group is P4 32 o r P4,32 ; t h e arrangement of t h e e i g h t Fe atoms on t h e t e t r a h e d r a l sites & c ) i s n o t modified whereas t h e twelve Fe atoms occupy t h e 1 2 ( d ) p o s i t i o n s and f o u r L i atoms t h e ( 4 b ) p o s i t i o n s ; t h e r e f o r e t h e w e l l known 1:3 o r d e r appears on t h e B s i t e s . Lithium f e r r i t e s p r e s e n t s a c r y s t a l l o g r a p h i c o r d e r - d i s o r d e r t r a n s i t o n i n t h e temperature range 1008 t o 1038 K; t h e s t r o n g e s t A-B superexchange i n t e r a c t i o n g i v e s r i s e t o a Curie temperature o f 955 K.
S t u d i e s o f Li-Ti-Zn f e r r i t e s have been a l r e a d y r e p o r t e d /2/ /3/ /4/ /5/;
n e v e r t h e l e s s o n l y s m a l l s u b s t i t u t i o n s o f t i t a n i u m have been c o n s i d e r e d e x c e p t i n t h e work of Konwicki and Makolagwa /6/. I n t h i s s h o r t communication, t h e magnetic p r o p e r t i e s of p o l y c r y s t a l l i n e a r e p r e s e n t e d , more d e t a i l s w i l l be given i n a forthcoming paper.
I1
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SAMPLE PREPARATIONP o l y c r y s t a l l i n e samples were prepared from Li2C03, TiOp, ZnO, Fez03 powders, a l l of h i g h p u r i t y , using t h e c o n v e n t i o n a l ceramic technique. The raw powders were mixed i n a s t e e l b a l l m i l l , c a l c i n a t e d a t 900°C d u r i n g 2 h o u r s , wet m i l l e d d u r i n g 4 hours.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1985684
C6-438 JOURNAL DE PHYSIQUE
The powder was p r e s s e d i n t o d i s k shapes ( 2 5 mm d i a m e t e r , 5 mm t h i c k n e s s ) . The specimens were s i n t e r e d a t 1050°C f o r 6 hours i n oxygen atmosphere and s l o w l y c o o l e d i n t h e same atmosphere (lOO°C/h). To reduce t h e s i n t e r i n g temperature and t h e l o s s of Li and 0 2 , and t o o b t a i n samples of h i g h d e n s i t y / 2 / , a weak amount of B i a w a s added ( = 0.002/formula u n i t ) . To avoid e x c e s s of i r o n t h e s t e e l b a l l wear was cor- r e c t e d . According t o t h e chemical a n a l y s i s , t h e samples d i d n o t c o n t a i n Fe2+ i o n s ; X r a y s measurements have confirmed t h e presence of s p i n e l phase only. Note t h a t s e v e r a l specimens were quenched i n a i r from a temperature which v a r i e d from 400 t o 900°C. The bulk d e n s i t y of t h e specimens was n o t l e s s t h a n 97 % of t h e t h e o r e t i c a l value. The c a t i o n d i s t r i b u t i o n which was proposed f o r low t i t a n i u m c o n t e n t s /2/ was assumed a s s t i l l v a l i d i n our c a s e ; it is w r i t t e n :
and o c t a -
Fig. 1
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T h e m a g n e t i c moment M ( m e a s u r e d i n 9 . 8 kOe) v e r s u s t e m p e r a t u r e f o r z = 0 . 1 ; t h e t v a l u e s a r e 1 . 1 ( c u r v e l ) , 1 . 2 ( c u r v e 2 ) , 1 . 2 5( c u r v e 3 ) . 1 . 3 ( c u r v e 4 ) , 1 . 4 ( c u r v e 5 ) . I11
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EVIDENCE OF FOUR CHARACTERISTIC TEMPERATURES.The magnetization (M) and t h e magnetic s u s c e p t i b i l i t y x ( a l l t h e r e s u l t s given i n t h i s paper correspond t o one mole of t h e Li0.5Fe2.504 t y p e ) were measured i n a magnetic f i e l d of 9.8 kOe from l i q u i d n i t r o g e n t o 1200 K u s i n g a magnetic balance.
The r e s u l t s a r e p r e s e n t e d i n F i g u r e s 1 and 2. The M(T) c u r v e s p r e s e n t a long t a i l and t h e d e t e r m i n a t i o n o f t h e Curie temperature (Tc) is more o r less accurated.
Nevertheless it is c l e a r t h a t f o r both z i n c c o n c e n t r a t i o n s , two r e g i o n s ( t > 1.2 f o r z = 0 and t > 1 f o r z = 0.1) a r e found where Tc becomes c o n s t a n t when t h e t i t a n i u m c o n t e n t i n c r e a s e s . The observed limits of T i n c r e a s e w i t h t h e z i n c c o n t e n t and are e q u a l t o (220
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20)K ( z = 0 ) and (400 50)K ( z = 0.1) r e s e c t i v e l y . S u c h a behaviour which is i n c o n t r a d i c t i o n w i t h the, d e c r e a s i n g of t h e Feg+ c o n t e n t w i l l beexplaFned i n a n e x t paper. Note
t h a t when z = 0 , our Tc v a l u e s a s s o c i a t e d w i t h low t i t a n i u m s u b s t i t u t i o n s a r e i n good agreement with previous d a t a of Blasse /2/. Furthermore a s p r e v i o u s l y n o t e d by t h e same a u t h o r , a n anomalous P t y p e M(T) curve 1s fourla f o r t = 0.9 while a N t y p e curve is observed f o r t = 1.
Below Tc t h e M(T) c u r v e s e x n i b i t an a b r u p t change of e v o l u t i o n a t a t e m p e r a t u r e n o t e d TSR o n l y f o r t h e h i g h t i t a t i u m c o n t e n t s . A s f o r lower c o n c e n t r a t i o n ( z = 0 , t > 0 . 7 ) , non c o l i n e a r magnetic s t r u c t u r e s have been proposed a t low t e m p e r a t u r e s by J.L. Dormann /5/, it is r e a s o n a b l e t o c o n s i d e r t h a n TsR o r i g i n a t e s from c a n t e d magnetic o r d e r s .
F i g . 2
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R e c i p r o c a l m a g n e t i c s u s c e p t i b i l i t y v e r s u s t e m p e r a t u r e f o r z = 0 . 1 ; t i s e q u a l t o 0 ( c u r v e 1 0 ) ; 0 . 2 ( 9 ) ; 0 . 4 ( 8 ) ; 0 . 6 ( 7 ) ; 0 . 9 ( 6 ) ; l ( 5 ) ; 1 . 1 ( 1 ) ; 1 . 2 ( 2 ) ; 1 . 2 5 ( 3 ) ; 1 . 3 ( 4 ) .A t h i g h e r t e m p e r a t u r e s , t h e X-l ( T ) v a r i a t i o n (Fig.2) p r e s e n t t h r e e behaviours s e p a r a t e d by T1 and T2 s t i l l o n l y f o r h i g h t i t a n i u m r a t e s . T2 is observed a s c o n s t a n t and e q u a l t o (1025
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20)K ; f u r t h e r m o r e t h i s v a l u e a g r e e p e r f e c t l y t o t h e c r y s t a l l o g r a p h i c o r d e r - d i s o r d e r.
t r a n s i t i o n t e m p e r a t u r e mentioned i n t h e i n t r o d u c t i o n . X-ray i n v e s t i g a t i o n s have confirmed t h e presence of s u p e r s t r u c t u r e l i n e s which r e v e a l e d an o r d e r e d c a t i o n i c d i s t r i b u t i o n o v e r t h e o c t a h e d r a l s i t e s . On t h e o p p o s i t e , T1 is observed a s a d r a s t i c f u n c t i o n of b o t h z i n c and t i t a n i u m c o n t e n t s .A l l p r e v i o u s r e s u l t s concern s l o w l y c o o l e d specimens ; t h e i n f l u e n c e of t h e quenching on t h e magnetic s u s c e p t i b i l i t y above t h e Curie p o i n t h a s been s t u d i e d f o r t h e s u b s t i t u t i o n s z = 0.1 ; t = 1.2. The r e s u l t s a r e summarized i n t h e f i g u r e 3 ; when t h e quenching t e m p e r a t u r e Tq i s changing from 400° t o 900°C, Tc d e c r e a s e s r a p i d l y ; it becomes s m a l l e r t h a n 100 K when t h e quenching t e m p e r a t u r e is h i g h e r t h a n 700°C. T2 is observed o n l y f o r t h e s l o w l y c o o l e d sample ; Ti is f u n c t i o n a l s o of t h e quenching t e m p e r a t u r e , it d i s a p p e a r s when Tq is h i g h e r t h a n 600 K.
I V
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CONCLUSIONMagnetic p r o p e r t i e s o f t h e Li-Ti-Zn systems have been i n v e s t i g a t e d w i t h i n t h e h i g h t i t a n i u m s u b s t i t u t i o n . Two r e g i o n s ( t
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1.2 f o r z = 0 and t > 1 f o r z = 0.1) were observed w i t h f o u r c h a r a c t e r i s t i c t e m p e r a t u r e s : Tc (Curie t e m p e r a t u r e ) which does n o t d e c r e a s e w i t h t h e diamagnetic i o n s u b s t i t u t i o n ; TsR which is s m a l l e r t h a n Tc is a t t r i b u t e d t o t h e o n s e t o f non c o l l i n e a r magnetic s t r u c t u r e ; T p is independent o f t h e z i n c and t i t a n i u m c o n t e n t s , it is t h e o r d e r - d i s o r d e r t r a n s i t i o n temperature a t which t h e 1 : 3 o r d e r on t h e B s i t e s d i s a p p e a r s ; t h e l a s t c h a r a c t e r i s t i c temperature(TI) l i e s between Tc and Tp, it is f u n c t i o n of both z i n c and t i t a n i u m c o n t e n t s , it is s t r o n g l y modified by t h e quenching temperature.
JOURNAL DE PHYSIQUE
Fig. 3
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Influence of the thermal treatment on the magnetic susceptibility : slowly cooled sample ( 1 ) ; two quenching temperatures 600°c ( 2 ) and 900°C (3). For the three cases z = 0.1 and t = 1.2.REFERENCES
/1/ Brunel, M. and de Bergevin, F.. C.R.Acad.Sc.Paris 285 (1964) 5628.
/2/ Blasse, G., Philips Res.Rep.Supp1.
3
(1964) 96/3/ Baba, P.D., Argentina. G.M., Courtney, W.E., Dionne G.F., Temme, D.H. I.E.E.E.
Trans.Mgn. MAC-8 (1 972) 83
/4/ NoguGs, M., Dormann. J.L., Perrin, M., Simonnet, W., Gibart, P., I.E.E.E.
Trans.Mag., MAG-15 ( 1 9 7 9 ) 1729.
/5/ Dormann. J.L., Rev. Phys. Appl., 12 (1980) 1113.
/6/ Konwicki, M., Makolagwa,S., J. Phys. 32 (1977) C1-271.
