The effect o f cobalt substitution on structure and magnetic properties o f nickel feưite

VNU Journal o f Science, Mathematics - Physics 25 (2009) 153-159

The effect o f cobalt substitution on structure and magnetic properties o f nickel feưite

N g u y e n Khanh D u n g ' ’*, N g u y e n H o a n g Tuan*

^ỉndusĩn' University', Ho Chi Minh City.

Ỉ 2 Nguyen Van Bao, Ward 4, Go Vap District, ĩỉochim inh city\ Vietnam Can TỈU) University, 3-2 Street, Can Tho city, Vietnam

Received 15 August 2009

Abstract. A series o f cobalt d o p e d nickel íeưile with composition of Nii.xCoxFe204 with X ranges I'roni 0.0 to 0.8 (in steps of 0 .2 ) was prepared by using co*precipitation method and subsequently sintered, annealed at 600“c for 3h. The iniluence of the Co content on the crystal lattice parameter, ihe stretching vibration and the magnetization of specimens were subsequently studied. XRD and

F T IR w e r e u s e d to i n v e s t i c a t c structure and c o m p o s i t i o n v a r i a ti o n s o f the s a m p l e s . A ll s a m p l e s

were found to have a cubic spinel structure. TEM was used to study morphological variations. The results indicate that the average particle sizes are between 29-35 nm. B-H hysteresis measurement

w a s caiTied o u t at r o o m te m p e r a tu r e u n d er f ield o f 5 k O e a n d this m e a s u r e m e n t w it h the in cr ea se

of Co concentration yields the monotonic increase of saturation magnetization (Ms) and coercive field (lie ). Ferrites with such behavior are important for magnetic recording media, microwave applications, environment and mcdical biology [1-3]. In view of this, we have studied the various properties of Co doped Ni ferrite.

1. I i i t i o d i i v l i u i i

N 1FC2O 4 has cubic inverse spinel structure with ions occupy octahedral B - site and ions occupy both tetrahedral A - sites and octahcdral B - sites [4]. N ickel ferrite has been prepared by standard ceramic route, rh a t are parliclc size m icrom eter, low saturation m agnetization and low cocrcivity. I'o our know ledge, the systematic investigation o f the m agnclic and electrical properties o f N i i . x C o x F c204 w ith X varied from 0 to 0.8 in steps o f 0.2 has not been reported so far. Further Ni-Co i'crrite shows the good m agnetostriclive properties am ong all the ferrite family. T he studies on doping o f good m agnctostrictive material into the highly res.slive nickel ferrite is one o f the im portant phase for consideration o f challenging maiinetoclcclric materials. T herefore by k eeping this view in our mind \vc have p roposed the studies on structural analysis and m agnetic properties o f C o - N i ferrite with the above m entioned co m positions by CO - precipitation m ethod, a n e w m ethod for preparation o f ferntc [5-6].

The results show n prep ared Nii.xCo,xFe204 p o w d er íe ư ite had the particle sizes in nanom eters and good magnetic properties:

- Saturation M agnetization Ms about 47-67 emu/g,

Corresponding author. E-mail; nkdung@yahoo.com 153

54 N.K. Dung. N fl Tuan / I'NU Journal o f Science, Maihcrmitics - Physics 25 (2009) Ỉ 53-Ỉ 59

- Cocrcivitv H r from 3 1 O c (w ith x - 0 . 0 ) to 871 O c (with x=0.8), - Average loimitudinal M agnetostriction 1.;: = (80-120). 10

- M agnctom echanic Ọ uality Q = 3 1 0 0 (with x=^0.0)

2. Experim ental

2.7. S yn th esis o f N i-C o p o w d e r f e r r ite

A series o f cobalt doped nickel ferrite with com position o f Nii_xCoxFe:0 4 w ith X ranges fro m 0.0 to 0.8 (in steps o f 0.2) w as prep ared b y co-precipitation method. F or the sake o f simplicit>, ihc samples are labeled viz. NF for X ^ 0.0, N TC02 for X == 0.2, N F C 0 4 for X 0.4, N F C 0 6 for X = 0 .6 and N FC 08 for X = 0.8. T he chem ical reag e n ts used were N 1CI2.6 H 2O, C 0 CI2.6 IỈ2O, F e C l3.6 I l 2 0 . A ll the chem icals were dissolved in w ater w ith concentration o f 0.8 mol, 0.4 mol o f 10ns Co"’ and N r ' , 0.48 mol solution o f sodium h y d ro x id e w as prepared and slow ly added to the salt solution drop wise with steady stirring. T he reaction w as p erform ed at 80^c and pH values in the range (12-14) k eep up constant for three hours. A precipitation im m ediately formed in the solution:

O .S N iC K .ó íh O + O.2 C 0 CI2.6 H2O + 2FC2C 15.6 H : 0 + 8N aO H N i0 8C o 0,2Fe2O 4Ì + 8NaCl + 2211:0

▼

After the precipitation w as ta k en b y magnet and the product w as w ashed several time with distilled waicr. Finally it was an nealed in oven at 6 0 0 ^ for 3 hours.

2.2. M easu rem en ts o f p r o p e rtie s o f ỈSi-Co fe r r ite

'ĩ h e morpholo^ỵy o f the sam ples w as perform ed by X-ray d iffractom eter iX R D ), Fourier t r a n s f o r m infrared (FT-IR) transm ission spectra an d Transm ission Electron M icroscope (T E M ). D cbey S cherrer formula was used to determ ine the particle size o f the prepared sam ples. T he magnetic characterization w as perform ed by vib ratin g sample m a gnetom e ter (V SM ).

3. Results and discussion

3.1. x~ ray diffraction

X-ray pow der diffraction (X R D ) patterns o f N ir x C o x Fe204 (w ith X = 0, 0.2, 0.4, 0.6, 0.8) are show n in Fig. 1. F rom this Fig. the follow ing reflection planes are show ed: (111), (220), (311), (222), (400), (422), (511) and (440). T hese p la n es are indications o f the presence o f a spinel cubic sừaicture.

T he diffraction lines co rresponding to a cubic, spinel-type and cĩ7 Stalline p hase provides clear evidence ol the ibm ialion o f solid so lu tio n N iFc204.

N.K. Dun^. N.ỊỊ Tuan / VNU Journal o f Science, Mathematics ' Physics 25 (2009) Ĩ 53-159 155

''ùQ, c '3

no

UM)*X) 80 70 60 50 40 -V)

20 10 0

____

''.-‘"wAwwkv

10 20 30 40 50

^ X = 0.8 X = ).6

^ X = 0.4 X - 0 . 2

^ x = 0.0

60 2 Theta - Scale

Fig. 1. XRD powder diffraction patterns o f Nii_xCOxFe204.

From Fig.2 it is observed that lattice param eter varies from 8.334 Ả to 8.382 Ả with increasing Co content and they arc tabulated in Table 1. This increase o f lattice p aram eter with C o due to the diftcrcnce in ionic sizes o f the co m ponent ions. The ions have larger ionic radius (0.78 Ả) than Ni"' (0.74 A) and Fe^' (0.67 Ẳ) ions.

Ỉ-Ig. 2. Lattice parameters ot Ni|.xCOxl‘e204.

Tabic 1. Calculated lattice parameter ‘a \ X-ray density ‘D x \ Actual density and Relative density of Nii.xCOxFe204 ferrites

Sample Particle size (nm)

Lattice parameter (A“)

X-ray density ‘Dx’

(g/cm^)

Actual D \ (g/cm’)

Relative density D’x/ ‘D’x (%)

sli- 29 8.334 5.4 5.3 98.2

SIFC02 33 8.343 5.4 5.2 96.3

NI1-C04 30 8.362 5.3 5.2 98.1

MFC06 33 8.371 5.3 5.2 98.1

MFC08 35 8.382 5.3 5.1 96.2

156 N.K. Dung, N IL Tuan / VNU Journal ofScietice, Mcuhemcitics - Physics 25 (2009) Ỉ53-Ỉ59

T he X-ray density or theoretical density w as estimated by using the relation [6 ]'

X -ray density X ... ( n

N ^ . v

W here, A is the atom ic w eights o f all the atoms in the unit cell, V is v o lu m e o f the unit cell a n d N is the A v o g ad ro ’s number.

Sincc each prim itive unit ccll o f the spinel structure contains 8 m olcculcs, the X -ray density. ‘D x ’ was d c t c m i i n e d according to the following relation and IS shovvTi in Table 1.

8M

D , (2 )

N ^ . a ’

Where, M is m olccular w eight o f the particular ferrite, Na is the A v o g a d r o ’s n u m b e r an d is the volume o f the cubic unit cell.

From Fig.2, it is observed that X-ray density ‘Dx’ decreases with addition o f C o “* ion co n ten t, w hich m ay be attributed to the ionic radii o f constituent ions causing increase in lattice p a r a m e te r and the densities o f pure cobalt ferrite (5.29 g/cm^) and pure nickel f e m te (5.38 g/cm^).

The obtained X R D patterns o f the Ni-Co ferrites are shown in F i g . l . Conscqucỉiily, on e can ob ta in the average particle size, from the broadening elTecl o f the most intense p eak e m p lo y in g ihc SchcnxT formula as [6],

0 .9 X

d = --- — --- (3)

B 20 COS0

w here B20 is the full w idth h a lf m axim um (rad), \ the w avelength o f the X -ray, 0 the an g le b etw een the incident and d iff ra c tc d b e a m s (d e g r e e ) a n d d the p a rtic le size o f the s a m p l e ( n m ) (in l a b l e 1).

3,2, F T -IR sp ectro sco p y

The band w av cn u m b c r V|. V., (Table 2) generally obsen^ed in the range 6 0 0 - 5 5 0 cm c o ư e s p o n d s to an intrinsic stretching vibrations o f the metal at the tetrahedral site, Mịctra <-> o , w hereas th e vs - lowest band, usually observed in the range 4 5 0 - 3 8 5 cm is assigned to o ctahedral-m ctal strctchm g.

Mocta o [6]. T he decrease o f w av en u m b e r with the increase o f C o “* is show n in l*ig.3.

Table 2. The IR spcctra analysis for the studied samples

Sample V| (em ') V²(em ')

NF 596.15 428.12

NFC02 595.20 424.75

NFC04 595,37 420.65

NFC06 596.78 422.25

NFC08 593.02 420.72

N K. Dunịĩ, N.ỉi. Tuan / VNU Journal o f Science, Mathematics - Phvsics 25 (2009) Ỉ53-Ỉ59 57

W avcnum ber cm ’ Wavenumber cm'^

Fig. 3. FT-IR spectra of ferrite NiFe204 (left) and Nio 2Coo gFe204 (right).

3,3. T E M a n a lysis

a

Nf 4 M p iffc U

M iiV »• u«;«t <•

Fiu. 4. TEM Micrograph of: (a) NiFc204, (b) Nio4Coo6F'c204. (c) Nio2CoosFe204 annealed at 600°c.

T l ' M vvai> Ubcd to invci>tigalc llic l u u i p l i u l o g y a n d m i c i u g i a p h b o f v a i i u u b s a m p l e s . M i c m icrographs arc show n in Fig.4. A broad size distribution is observed with 32 ± 3 nm.

Fig.5 sliovvs hysteresis loops for Nii.xCOxFc204 nanoparticles at room tem pcrature.T hese plots show that an increase in Co^* d o p in g yields monotonic increase in the saturation magnetization o f Ni- fcrrite which may be due to the substitution o f ions by C o ‘" on the octahedral sties. Therefore, the increasing Co^* concentration (x) on the octahcdral sites m ay result in an increasing magnetic mom ent per form ula o f NÌị.xC0 xFc204 and equivalently, an enhan c em en t o f magnetization [7].The depcndencc o f saturation m agnetization Ms as a function o f concentration is shown in Fig.5. At room tem perature N iF c 204 show s a saturation m agnetization M s = 35.3 (em u/g) while N io 2C oo8p e 204 exhibits M s = 60.1 (em u/g) (in table 3).

Table 3. Room temperature parameters: Saturation magnetization ( M s ) , Coercivity ( H e ) ,

X H( (Oe) M s (emu/e) Mr(emu/g) K (erg/g)

0.0 31 35.3 7.3 5.5,10'

0.2 359 38.1 12.4 6.9.10’

0.4 740 49.1 20.0 1.8. 10'

0.6 835 55.7 26.4 2.3.10'

0.8 871 60.1 27.1 2 .6. 10’

158 N.K Dung. N.H. Tuan ' VNIJ Journal of Science, Mathemaiics - Physics 25 (2009) Ì55-Ì59

3.4. M a u n e tiza iio n ỉĩic a su re m ư n ís:

u 3

i

c

o N

•«11#

c 60

40 20

0

-20

-40 -60

... ... ... ...

- . ... ...-...—... /

V : :

Ị - ... -T-... ... ...;■

■” .... .... *•.... ... --- ...--- ... ... .

\= 0.8

x= 0.6

x= 0.4 x =0.2

x= 0.0

- 10000 -5000 0 5000

M a g n e t i c fie ld s t r e n g t h

10000

Fig. 5. Hysteresis loops for all samples of Nii.^Co^Fe204 ferrite system.

I'herc will be a d e p e n d e n c e o f an isotropy constant K on the C o “' ion concentration X, which can be evaluated by using the relation and is show n in table 3 with K = M

Ĩ

M agnetic structure o f ferrite Nii.xC0 xFc204 is decribcd follow ing [8J:

--- ► ^ ^ --- <---

Ỉ - V ' [ N i ^ ‘ , „ F c-'‘ ] 0 ^

tetrahedral octahedral

The magnetic m o m en t o f a ion C o ’ * is equal to 3|.iB, during it is 2 |.iB for a ion and 5 ftB for Fe^'. When X increased this leads to the com pensation o f ion in the tetrahedral and octahcdral location. That led to in c re asin g o f total magnetization o f a m olccule NÌị.xCOxFc204 and hcncc there is increasing o f Ms (table 3).

A nother side, it is k n o w n that the m agnetizing proccss o f hard ferrite consisting o f sintile domain particles is the rotation p ro c e s s o f m agnetization vectors o f dom ain, then cocrcivity is determined as follows: 11^ = o ^ + b ( N , - N , ) M , + c ^

M g

w here a, b, c are constants; Nị an d are dem agnetization factors determ ined along tw o perpendicular directions;

x$

^- m agneto stric tio n an d T- mechanical strain.

\.K . Dung. N.ỈỈ. Tuan / VNU Jo u n u d o f Science, Mathematics - Physics 25 (2009) Ỉ53-Ỉ59 159

'I'hc first term in above expression c o ư e s p o n d s to the c o n trib u tio n o f magnetocrystalline a n is tn ro p y o f material, the s e c o n d o n e IS giv en by s h a p e a n is o t r o p y o f c ry s t a ll in e p a rticle s (do m a in s) a n d th e third o n e IS o r g in a t c d fro m the a c tio n o f elastic m e c h a n i c a l d e f o r m a t i o n . In fact, th e first term plays a dccidcd role for creating high coercivity o f materials, the s e c o n d te rm can take part o f several tens perccnt o f H( and the last one w hereas can only reach several h u n d re d s o f gauss.

Thus, the increasing o f C o-conccnlration led to the increasing o f a n iso tro p y property o f ferrites Nii_^C0 xFe:0 4 , hence it w as the increasing o f He-

T he increasing o f I ỈC p roved that the soft magnetic p roperty o f ferrite N i F e 204 changed to the hard m a sn elic propertv o f f e m t e C

0

^ĨC

2

^O

4

^.

N i-Co fcrn le sam ples m anifested m a g netostnctive p ro p e rty w ell. T he longitudinal m agnetostriction ( w as m e asure d in accordance with sensor W h e a s to n bridge m ethod [9] ) o f Nii.xCo^Fc:0 4 Icrrites w as h , - (80 -120).10’^ (with X = 0.6 - 0.8).

The M aíínetom cchanic Q uality w as delcrm inated by follow ing ex p re s s io n : Q =-------, with

^Cu ” ^Fer

I, IS the electric induction o f a coil torus, m easured on the d ev ice 819 H ig h P recision L C R M eter in Institute o f Physics in Ho Chi M inh City, CO is measured freq u en cy , w h e r e valuable 700H z; Rcu and Rf er resistance o f the cop p er coil w ithout and with ferrite toroid co re, m e asure d by the method i'ov W hcaston briduc. T h e M agnelom echanic Quality o f N i0 F e 203 w as 3100.

4. ('on clusion

Spinel ferrite N ii,x C o J 'e 204 was synthesized successfully b y c o -p recip itatio n m ethod. X-ray diffraction study sh o w s the presence o f cubic spinel. T he increase o f C o*' ion co n ce n ư a tio n yields the inonotonic increase o f Ms, H('. M agnetic m easurem ents show the stu d ie d s y stem m ay be suitable for magnetic recording m e d ia application w ith some im provem ents.

A c k n o w le d g e m e n ts : T h is w ork w as supported by the Institute o f P h y sics in I ÍO Chi M m h City.

Ucfci cntc.s

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