- Email: [email protected]
Synthesis, Magnetic Properties and Microstructure of Ni-Zn-Cr Ferrites Doped with Lanthanum
JOURNAL OF RARE EARTHS V o l . 2 5 , S u p p l . , Jun. 2007, p . 2 3 2
Synthesis, Magnetic Properties and Microstructure of Ni-Zn-Cr Ferrites Doped with Lanthanum Zhou Xiangchun (A*-&I2, Li Liangchao ( * b%)' * , Liu Hui (3j Xu Feng (4% %)I,
Jiang Jing ( %
#)I,
*
( 1 . Zhejiang Key Laboratory for Reactive Chemistry on Solid Surface, Zhejiang Normal University, Jinhua 321004 , China ; 2 . College of Chemistry and Environmental Engineering , Yangtze University, Jingzhou 434020, China ) Abstract: The precursors consisted of Ni2 , Zn2 , Cr3 , Fe3 and La3 ionic citrate were prepared by sol-gel process. +
+
+
+
+
Nanocrystalline powders of Zno.4NiO.sCro.5Fel, 5 0 4 and Zno.4Ni".6Cro.~Lao.02Fe,.4xO~ were obtained at low sintering temperatures. The process that amorphous precursors translated to crystalline ferrites was researched by means of DSC-TG. The structure, morphology and magnetic properties of the obtained products were characterized by X-ray diffractometer (XRD) , transmission electron microscope (TEM) and vibrating sample magnetometer (VSM) . The results showed that the sintering temperature and La doping had an obvious effect on the crystallite size and magnetic properties of samples. The crystallite size of Ni-Zn-Cr ferrites varied from 14.6 to 23.1 nm in the sintering temperature range from 400 to 800 "c , and the crystallite size varied from 13.2 to 19.1 nm for La-doped Ni-Zn-Cr ferrites in the same condition. The saturation magnetization of samples increased with sintering temperature, while the variation of coercivity had a reverse trend.
Key words : nanocrystalline ; Ni-Zn-Cr ferrite ; sol-gel ; La doped ; rare earths Article ID : 1002 - 0721 (2007) - 0232 - 04 Document code : A CLC number : 0621 .23
Ni-Zn ferrites are one of the most versatile soft magnetic materials for general use, such as microwave devices, power transformers in electronics, rod antennas, read/write heads for high-speed digital tape, etc . [ 1 s 2 1 . Recently, the materials are studied extensively as high frequency devices because of their high resistivity, low eddy current losses, high-Curie temperature, mechanical hardness and chemical stability[3-6i.The replacement of Fe3+ with Cr3' in the ferrite presumable leads to decrease of both porosity and grain size, the bulk density i n ~ r e a s e ' ~ so ' , the appropriate content of Cr substitution is propitious to obtain a lesser grain size. It seems that small rare earth ( RE ) additions play an important role in modifying structure and magnetic properties of ferrites due to the magnetocrystalline anisotropy in the rare earth doped compounds and the RE-Fe interaction (4f-3d coupling) ['I . Till now, some researches have been carried out about the preparation and magnetic properties of ferrites . But the effect of La doped on the structure, grain size, morphology and magnetic properties for Ni-Zn-Cr ferrites was reported less. In the present work, an inves-
*
tigation was made to obtain La-doped Ni-Zn-Cr ferrites via sol-gel method and revealed the influence of La doping on the obtained samples.
1 Experimental The nanocrystalline ferrites Z ~ . ~ N i ~ . s CFel r o.5.0~4 and Zno.4Ni0.6Cro,5La,,02 Fel .4x0 4 were synthesized by the citrate precursor method. The starting materials were analytically grade pure of Zn ( N o 3 1 2 6H20, Cr( N03)3 9H20, Fe ( N o 3 ) 3 * 9H20, Ni ( No3 ) 2 * 6H20, La(N03)3*6H20and citric acid. At room temperature, the stoichiometric amounts of the metal nitrates were dissolved in distilled water under continuous stirring, then appropriate citric acid was added and controlled the pH = 8 by aqueous ammonia. After the solution was evaporated to sol at 80 "c, drying the sol to gel at 100 "c, and the products were obtained by sintering the gel at different temperatures in furnace. The structure of samples was determined by Philp~-PW3040/60model X-ray diffractometer (XRD) using Cu KaI radiation ( A = 0.15405 nm) at a scan-
Received date : 2006 - 10 - I0 ; revised date : 2007 - 04 - 15 Foundation item: Project supported by the Natural Science Foundation of Hubei Province (2004ABA104) and the Science and Technology Key Project of Zhejiang Jinghua City (2004-2-157) Biography: Xu Feng (1981 - ), Male, Master candidate; Research direction: electronic and magnetic function materials Corresponding author (E-mail: [email protected])
Xu F et a1 . Synthesis, Magnetic Properties and Microstructure of Ni-Zn-Cr Femles Doped with Lanthanum
-
ning speed of 4 (”) emin-’ in the range of 2 8 = 15” 80”. Magnetization measurements were performed at room temperature in a vibrating sample magnetometer (VSM , Lakeshore 7404) in 10 kOe applied field. The morphology and particle sizes of the obtained products were characterized by transmission electron microscope (TEM , JEOL-2010) . The thermal decomposing of citrate precursors were carried out by a TGA/SDTA851 thermal analyzer at a heating rate of 20 “c smin-’ with the temperature range 25 800 “c in an air atmosphere.
-
2 Results and Discussion 2.1 TG/DTG/DSC analysis The TG/DTG/DSC curves of the dried gel for samples are shown in Fig. 1. The decomposition reaction is strongly exothermic as shown in DSC curve. The TG curve shows that the largest weight loss of about 86.08% closed to theoretical value 86.32% occurs in the temperature range of 160 “c to 240 “c, corresponding to the decomposition reaction of the citrate precursor. The minor weight loss over 240 “c is corresponding to the combustion of residual citric and a small quantity of carbon. The maximal reaction speed and exothermic peak appear at about 220 “c observed from DTG and DSC, while for pure citric acid, the results of DTA and TG showed that the exothermic reaction takes place at about 500 “c, which indicated that there exists an autocatalytic anionic oxidation-reduction reaction between the nitrate and citrate system[g1.
233
XRD patterns shows that nano-sized products have the cubic spinel crystal structure. The diffraction peaks are broadened with decreasing of the sintering temperature, and the crystallite size of the ferrite increases with temperature. It is because the products have a more complete crystallization under the higher sintering temperature. The citrate precursor for Zno.4Ni0.6 Cro,,Fel.504calcined at 400 800 “c ( i n step of 100 “c ) shows an increase in crystallite size ( 14.6 - 16.2 - 1 6 . 9 - 19.4 - 2 3 . 1 nm) calculated by the DebyeScherrer formula (Fig. 2 ) , and for Z ~ . ~ N i ~ , 6 C r o , & % . m Fe1,4804, the result also shows an increase in crystallitesize (13.2- 1 4 . 8 - 15.0- 1 6 . 4 - 19.1 n m ) at the same condition (Fig. 3 ) . Comparing the noumenon ferrites with La-doped femtes , the result shows that the former is larger than the latter at the same sintering temperature. The reason for that may be La3+ has a fine effect on crystallite size“’].
-
2.3 TEM analysis The
size
and
Nio.6Zno.4Cro.5Fel.&
morphology
as-synthesized
and Ni0.6Zn0.4 Cr0.5 L%.LFel.4 0
45 40 30
of
4
I
L
1
0
2.2 XRD analysis
10
Figs. 2 and 3 are the XRD patterns for citrate precursors of Zno.4Nio.6Cr0.5 Fel.5 O4 and Zno.4Ni0.6Cr0.5 L%,ozFel.4804 fenites calcined at the different ternperatures of 400, 500, 600, 700 and 800 “c for 2 h . The
20
40
30
50 60
70 80 9 I
204”) Fig.2
XRD patterns for Zno 4Ni0.6Cr~5Fe, 504at different sintering temperature
( 1 ) 400 g:; (2) 500 “c; (3) 600 T ; (4)700 “c; (5) 800 g: 40
1
0
-
-10
TG DTG ............. DSC
h
E .*
-20
-30
sE
n
-40 .................
.,.
0
-50 -24
o!
I
0
,
I
. , . 200
I
,
0
‘
400
0
’
I
’
600
I
’
I
10 20 30 40 50 60 70
800
80 90
204”) Fig. 1
TG/DTG/DSC curves of citrate precursor at a heating rate 10 9: smin‘’ in air atmosphere
Fig.3
XRD patterns for Z n o . 4 N i o . 6 C r ~ , , ~ . o F e l . 4at 8 0differ4
ent sintering temperature ( 1 ) 400 T; (2) 500 “c; (3) 600 “c; (4)700 g:; ( 5 ) 800
g:
JOURNAL OF RARE EARTHS, Vol. 2 5 , Suppl. , Jun . 2007
234
particles observed by TEM present in Figs. 4 ( a ) and ( b ) . The particles size is in the range of 15 25 nm and 10 20 nm in Figs. 4 ( a ) and ( b ) , respectively. They are consistent with the calculated results from XRD patterns by the Scherrer formula. The morphology of particles in Figs .4 ( a ) and ( b ) is spherical and appeared to be little agglomerated on the whole. Meanwhile, the particle size observed in Fig. 4 ( b ) is smaller than that in F i g . 4 ( a ) , which can indicate the La3' ion has a fine effect on crystallite size.
-
-
2.4 Magnetic properties analysis The magnetic properties are the most important properties for fenites depending on the processing conditions, microstructure, chemical composition and the type of the additives'". "I. Fig.5 shows the Hysteresis 5 La, . .02 loops for Zno .4Ni0.&TO. 5Fe1. 5 0 4 and Zno .4Ni0.6C ~ O Fel.4804ferrites calcined at 800 "c for 2 h . The values of saturation magnetization M , and coercivity H , are 41.571 emu * g - ' and 60.028 Oe for Zno.4Ni0.~Cro.5 F e l , 5 0 4 ( a ) ,37.739 e m u * g - ' a n d 53.431 Oe for Zno.4
es with the sintering temperature increases, which may be the particle sizes less than the critical size of a single domain. In this range of particle size, the H , variation depending on particle size can be explained by Stoner-Wohlfarth theory[l3l. According to the theory, the coercivity H , of a single domain particle is H , = 2 K / p o M , , where K is the magnetocrystalline anisotropy constant, p o is the universal constant of permeability in free space and M ,is the saturation magnetization of the nanoparticles. The increase of the sintering temperature results in complete crystallization, hence the value of K decreases, while the M , increases with the particle size, so the variation of K and M , seems to contribute to the H , corresponding decrease in accordance with Fig. 5 and Table 1.
Ni~.~Cro.5La,.02Fel .4804, respectively. The main contribution of magnetic properties derives from Fe3' on Bsites of ferrospinel , the nonmagnetic ~a~+ ions replaces Fe3+ ions (B-sites) resulting in decreasing the net overall magnetic moment ( m = m B - m A ) ,so the M , for La-doped ferrite is less. The Hysteresis loops for Zno.4 Ni0.6 La, o2 Fel,48 0, fenites calcined at different temperatures are shown in Fig. 6 . The values of M , and H , are listed in Table 1. It is can be seen that the saturation magnetization increases with the sintering temperature. The reason is that the energy of a magnetic particle in external field is proportional to its particle sizes via the number of magnetic molecules in a single magnetic domain, in addition, magnetic phase will be increased with the absorption of higher thermal energy. So the higher sintering temperature leads to the larger value of M , . While the value of H , decreas-
-75
-125
-25
25
75
125
Hi 10' Oe Fig. 5 Hysteresis loops for Z~.4Nio.6Cro.SFe,.50~4( 1) and &.4Nio.6 Cr0.Ja,, cnFe1.4804(2) at sintering temperature 800 "c 45.1 1 35 25 15 5
-5 -15 -25 -35
-10
0
-5
5
10
H/103 Oe
Fig.6
at difHysteresis loops for Z n o . 4 N i o . 6 C r o .mFel.4804 s~ ferent sintering temperature ( 1 ) 400 "c; (2) 600 "c; (3) 800 T
Table 1
Fig.4
TEM images of samples ( a ) Nio.6Zno.4Cro.5Fel >04 and (b) NiO.6 Zno.4Cro.5 La0.mFel 48 0 4 at sintering temperature 800 'c:
Values of magnetization and coercivity for Z b , 4 Nk,.6Cro.sL~.02Fel.~04 at different sintering temDerature
Temperature/%
400
600
800
Magnetization M./(emu*g.')
18.764
24.399
37.739
Coercivity (H,/Oe)
85.912
61.474
53.431
Xu F et a l . Synthesis, Magnetic Properties and Microstructure of Ni-Zn-Cr Fem'tes Doped with Lanthanum
[5] Zahi S , Hashim M , Daud A R .
3 Conclusion La-doped Ni-Zn-Cr ferrites nanoparticles were synthesized via the sol-gel method. All samples had cubic spinel structure. The M , increased, but the H , decreased as the sintering temperature increased for the doped sample, while the crystallite size was smaller than that of the undoped sample revealed that La3+ ions had a fine effect on crystallite size. Meanwhile, the M , and H , for doped samples was less than those of the undoped sample suggested that the magnetic properties could be tailored further by the introduced La3+ ions.
References : [ 1 ] Bhise B V , Dongare M B , Patil S A , Sawant S R .
235
X-
ray infrared and magnetization studies on Mn substituted Ni-Zn femtes [ J ] . J. Mater. Sci. Lett., 1991, 10
(15): 922. [ 21 Abraham T. Economics of ceramic magnets [ J ] . A m . Cerum . SOC . Bull., 1994, 73(8) : 62. [ 31 Anil Kumar P S, Shrotri J J, Kulkami S D, Deshparide C E , Date S K. Low temperature synthesis of Nio.8ZQ.z Fe204 powder and its characterization [ J ] . Muter. Lett., 1996, 27(6): 293. [41 Mangalaraja R V , Ananthakumar S , Manohar P, Ganam F D. Initial permeability studies of Ni-Zn femtes prepared by flash combustion technique [ J ] . Mater . Sci . Eng. A , 2003, 355(1-2): 320.
Synthesis, magnetic properties and microstructure of Ni-Zn ferrite by sol-gel technique [ J ] . J. Magn. Magn. Mater., 2007. [6] Secrist D R , Turk H L. Electrical properties of highdensity iron-deficient nickel-zinc ferrites [ J ] . J . A m . Cerum. S o c . , 1970, 53(12) : 683. [ 7 ] El-Sayed A M . Effect of chromium substitutions on some properties of NiZn ferrites [ J 1 . Ceram . Int . ,
2002, 28(6): 651. [8] Yang Y C, Kong L S , Sun S H , Gu D M , Cheng B P . Intrinsic magnetic properties of SmTiFelo[ J ] . J . App l . Phys . , 1988, 63(8) : 3702. [9] Yue Z X , Zhou J , Li L T , Zhang H G , Gui Z L. Synthesis of nanocrystalline NiCuZn ferrite powders by solgel auto-combustion method [J] . J . Magn . Mugn . Mater., 2000, 208(1-2): 55. [ l o ] Liu X S , Zhong W , Gu B X , Du Y W. Influences of rare earth La3' substitution on structure and magnetic properties of M-type strontium ferrites [ J ] . Rare Met. Mater , Eng . , 2002, 31(5) : 385. [ 11 ] Kondo K , Chiba T , Yamada S . Effect of microstructure on magnetic properties of Ni-Zn femtes [J ] . J . Magn . Magn . Mater . , 2003, 254 - 255 : 541. [ 121 Costa A C F M , Tortella E , Morelli M R , Kiminami R H G A . Synthesis, microstructure and magnetic properties of Ni-Zn femtes [J] . J . Magn . Magn. Muter., 2003,
256(1-3): 174. [ 131 Chen Q , Zhang Z J . Size-dependent superparamagnetic properties of MgFeZO4spinel ferrite nanocrystallites [J ] . Appl. Phys. Lett., 1998, 73(21): 3156.
Synthesis, Magnetic Properties and Microstructure of Ni-Zn-Cr Ferrites Doped with Lanthanum Zhou Xiangchun (A*-&I2, Li Liangchao ( * b%)' * , Liu Hui (3j Xu Feng (4% %)I,
Jiang Jing ( %
#)I,
*
( 1 . Zhejiang Key Laboratory for Reactive Chemistry on Solid Surface, Zhejiang Normal University, Jinhua 321004 , China ; 2 . College of Chemistry and Environmental Engineering , Yangtze University, Jingzhou 434020, China ) Abstract: The precursors consisted of Ni2 , Zn2 , Cr3 , Fe3 and La3 ionic citrate were prepared by sol-gel process. +
+
+
+
+
Nanocrystalline powders of Zno.4NiO.sCro.5Fel, 5 0 4 and Zno.4Ni".6Cro.~Lao.02Fe,.4xO~ were obtained at low sintering temperatures. The process that amorphous precursors translated to crystalline ferrites was researched by means of DSC-TG. The structure, morphology and magnetic properties of the obtained products were characterized by X-ray diffractometer (XRD) , transmission electron microscope (TEM) and vibrating sample magnetometer (VSM) . The results showed that the sintering temperature and La doping had an obvious effect on the crystallite size and magnetic properties of samples. The crystallite size of Ni-Zn-Cr ferrites varied from 14.6 to 23.1 nm in the sintering temperature range from 400 to 800 "c , and the crystallite size varied from 13.2 to 19.1 nm for La-doped Ni-Zn-Cr ferrites in the same condition. The saturation magnetization of samples increased with sintering temperature, while the variation of coercivity had a reverse trend.
Key words : nanocrystalline ; Ni-Zn-Cr ferrite ; sol-gel ; La doped ; rare earths Article ID : 1002 - 0721 (2007) - 0232 - 04 Document code : A CLC number : 0621 .23
Ni-Zn ferrites are one of the most versatile soft magnetic materials for general use, such as microwave devices, power transformers in electronics, rod antennas, read/write heads for high-speed digital tape, etc . [ 1 s 2 1 . Recently, the materials are studied extensively as high frequency devices because of their high resistivity, low eddy current losses, high-Curie temperature, mechanical hardness and chemical stability[3-6i.The replacement of Fe3+ with Cr3' in the ferrite presumable leads to decrease of both porosity and grain size, the bulk density i n ~ r e a s e ' ~ so ' , the appropriate content of Cr substitution is propitious to obtain a lesser grain size. It seems that small rare earth ( RE ) additions play an important role in modifying structure and magnetic properties of ferrites due to the magnetocrystalline anisotropy in the rare earth doped compounds and the RE-Fe interaction (4f-3d coupling) ['I . Till now, some researches have been carried out about the preparation and magnetic properties of ferrites . But the effect of La doped on the structure, grain size, morphology and magnetic properties for Ni-Zn-Cr ferrites was reported less. In the present work, an inves-
*
tigation was made to obtain La-doped Ni-Zn-Cr ferrites via sol-gel method and revealed the influence of La doping on the obtained samples.
1 Experimental The nanocrystalline ferrites Z ~ . ~ N i ~ . s CFel r o.5.0~4 and Zno.4Ni0.6Cro,5La,,02 Fel .4x0 4 were synthesized by the citrate precursor method. The starting materials were analytically grade pure of Zn ( N o 3 1 2 6H20, Cr( N03)3 9H20, Fe ( N o 3 ) 3 * 9H20, Ni ( No3 ) 2 * 6H20, La(N03)3*6H20and citric acid. At room temperature, the stoichiometric amounts of the metal nitrates were dissolved in distilled water under continuous stirring, then appropriate citric acid was added and controlled the pH = 8 by aqueous ammonia. After the solution was evaporated to sol at 80 "c, drying the sol to gel at 100 "c, and the products were obtained by sintering the gel at different temperatures in furnace. The structure of samples was determined by Philp~-PW3040/60model X-ray diffractometer (XRD) using Cu KaI radiation ( A = 0.15405 nm) at a scan-
Received date : 2006 - 10 - I0 ; revised date : 2007 - 04 - 15 Foundation item: Project supported by the Natural Science Foundation of Hubei Province (2004ABA104) and the Science and Technology Key Project of Zhejiang Jinghua City (2004-2-157) Biography: Xu Feng (1981 - ), Male, Master candidate; Research direction: electronic and magnetic function materials Corresponding author (E-mail: [email protected])
Xu F et a1 . Synthesis, Magnetic Properties and Microstructure of Ni-Zn-Cr Femles Doped with Lanthanum
-
ning speed of 4 (”) emin-’ in the range of 2 8 = 15” 80”. Magnetization measurements were performed at room temperature in a vibrating sample magnetometer (VSM , Lakeshore 7404) in 10 kOe applied field. The morphology and particle sizes of the obtained products were characterized by transmission electron microscope (TEM , JEOL-2010) . The thermal decomposing of citrate precursors were carried out by a TGA/SDTA851 thermal analyzer at a heating rate of 20 “c smin-’ with the temperature range 25 800 “c in an air atmosphere.
-
2 Results and Discussion 2.1 TG/DTG/DSC analysis The TG/DTG/DSC curves of the dried gel for samples are shown in Fig. 1. The decomposition reaction is strongly exothermic as shown in DSC curve. The TG curve shows that the largest weight loss of about 86.08% closed to theoretical value 86.32% occurs in the temperature range of 160 “c to 240 “c, corresponding to the decomposition reaction of the citrate precursor. The minor weight loss over 240 “c is corresponding to the combustion of residual citric and a small quantity of carbon. The maximal reaction speed and exothermic peak appear at about 220 “c observed from DTG and DSC, while for pure citric acid, the results of DTA and TG showed that the exothermic reaction takes place at about 500 “c, which indicated that there exists an autocatalytic anionic oxidation-reduction reaction between the nitrate and citrate system[g1.
233
XRD patterns shows that nano-sized products have the cubic spinel crystal structure. The diffraction peaks are broadened with decreasing of the sintering temperature, and the crystallite size of the ferrite increases with temperature. It is because the products have a more complete crystallization under the higher sintering temperature. The citrate precursor for Zno.4Ni0.6 Cro,,Fel.504calcined at 400 800 “c ( i n step of 100 “c ) shows an increase in crystallite size ( 14.6 - 16.2 - 1 6 . 9 - 19.4 - 2 3 . 1 nm) calculated by the DebyeScherrer formula (Fig. 2 ) , and for Z ~ . ~ N i ~ , 6 C r o , & % . m Fe1,4804, the result also shows an increase in crystallitesize (13.2- 1 4 . 8 - 15.0- 1 6 . 4 - 19.1 n m ) at the same condition (Fig. 3 ) . Comparing the noumenon ferrites with La-doped femtes , the result shows that the former is larger than the latter at the same sintering temperature. The reason for that may be La3+ has a fine effect on crystallite size“’].
-
2.3 TEM analysis The
size
and
Nio.6Zno.4Cro.5Fel.&
morphology
as-synthesized
and Ni0.6Zn0.4 Cr0.5 L%.LFel.4 0
45 40 30
of
4
I
L
1
0
2.2 XRD analysis
10
Figs. 2 and 3 are the XRD patterns for citrate precursors of Zno.4Nio.6Cr0.5 Fel.5 O4 and Zno.4Ni0.6Cr0.5 L%,ozFel.4804 fenites calcined at the different ternperatures of 400, 500, 600, 700 and 800 “c for 2 h . The
20
40
30
50 60
70 80 9 I
204”) Fig.2
XRD patterns for Zno 4Ni0.6Cr~5Fe, 504at different sintering temperature
( 1 ) 400 g:; (2) 500 “c; (3) 600 T ; (4)700 “c; (5) 800 g: 40
1
0
-
-10
TG DTG ............. DSC
h
E .*
-20
-30
sE
n
-40 .................
.,.
0
-50 -24
o!
I
0
,
I
. , . 200
I
,
0
‘
400
0
’
I
’
600
I
’
I
10 20 30 40 50 60 70
800
80 90
204”) Fig. 1
TG/DTG/DSC curves of citrate precursor at a heating rate 10 9: smin‘’ in air atmosphere
Fig.3
XRD patterns for Z n o . 4 N i o . 6 C r ~ , , ~ . o F e l . 4at 8 0differ4
ent sintering temperature ( 1 ) 400 T; (2) 500 “c; (3) 600 “c; (4)700 g:; ( 5 ) 800
g:
JOURNAL OF RARE EARTHS, Vol. 2 5 , Suppl. , Jun . 2007
234
particles observed by TEM present in Figs. 4 ( a ) and ( b ) . The particles size is in the range of 15 25 nm and 10 20 nm in Figs. 4 ( a ) and ( b ) , respectively. They are consistent with the calculated results from XRD patterns by the Scherrer formula. The morphology of particles in Figs .4 ( a ) and ( b ) is spherical and appeared to be little agglomerated on the whole. Meanwhile, the particle size observed in Fig. 4 ( b ) is smaller than that in F i g . 4 ( a ) , which can indicate the La3' ion has a fine effect on crystallite size.
-
-
2.4 Magnetic properties analysis The magnetic properties are the most important properties for fenites depending on the processing conditions, microstructure, chemical composition and the type of the additives'". "I. Fig.5 shows the Hysteresis 5 La, . .02 loops for Zno .4Ni0.&TO. 5Fe1. 5 0 4 and Zno .4Ni0.6C ~ O Fel.4804ferrites calcined at 800 "c for 2 h . The values of saturation magnetization M , and coercivity H , are 41.571 emu * g - ' and 60.028 Oe for Zno.4Ni0.~Cro.5 F e l , 5 0 4 ( a ) ,37.739 e m u * g - ' a n d 53.431 Oe for Zno.4
es with the sintering temperature increases, which may be the particle sizes less than the critical size of a single domain. In this range of particle size, the H , variation depending on particle size can be explained by Stoner-Wohlfarth theory[l3l. According to the theory, the coercivity H , of a single domain particle is H , = 2 K / p o M , , where K is the magnetocrystalline anisotropy constant, p o is the universal constant of permeability in free space and M ,is the saturation magnetization of the nanoparticles. The increase of the sintering temperature results in complete crystallization, hence the value of K decreases, while the M , increases with the particle size, so the variation of K and M , seems to contribute to the H , corresponding decrease in accordance with Fig. 5 and Table 1.
Ni~.~Cro.5La,.02Fel .4804, respectively. The main contribution of magnetic properties derives from Fe3' on Bsites of ferrospinel , the nonmagnetic ~a~+ ions replaces Fe3+ ions (B-sites) resulting in decreasing the net overall magnetic moment ( m = m B - m A ) ,so the M , for La-doped ferrite is less. The Hysteresis loops for Zno.4 Ni0.6 La, o2 Fel,48 0, fenites calcined at different temperatures are shown in Fig. 6 . The values of M , and H , are listed in Table 1. It is can be seen that the saturation magnetization increases with the sintering temperature. The reason is that the energy of a magnetic particle in external field is proportional to its particle sizes via the number of magnetic molecules in a single magnetic domain, in addition, magnetic phase will be increased with the absorption of higher thermal energy. So the higher sintering temperature leads to the larger value of M , . While the value of H , decreas-
-75
-125
-25
25
75
125
Hi 10' Oe Fig. 5 Hysteresis loops for Z~.4Nio.6Cro.SFe,.50~4( 1) and &.4Nio.6 Cr0.Ja,, cnFe1.4804(2) at sintering temperature 800 "c 45.1 1 35 25 15 5
-5 -15 -25 -35
-10
0
-5
5
10
H/103 Oe
Fig.6
at difHysteresis loops for Z n o . 4 N i o . 6 C r o .mFel.4804 s~ ferent sintering temperature ( 1 ) 400 "c; (2) 600 "c; (3) 800 T
Table 1
Fig.4
TEM images of samples ( a ) Nio.6Zno.4Cro.5Fel >04 and (b) NiO.6 Zno.4Cro.5 La0.mFel 48 0 4 at sintering temperature 800 'c:
Values of magnetization and coercivity for Z b , 4 Nk,.6Cro.sL~.02Fel.~04 at different sintering temDerature
Temperature/%
400
600
800
Magnetization M./(emu*g.')
18.764
24.399
37.739
Coercivity (H,/Oe)
85.912
61.474
53.431
Xu F et a l . Synthesis, Magnetic Properties and Microstructure of Ni-Zn-Cr Fem'tes Doped with Lanthanum
[5] Zahi S , Hashim M , Daud A R .
3 Conclusion La-doped Ni-Zn-Cr ferrites nanoparticles were synthesized via the sol-gel method. All samples had cubic spinel structure. The M , increased, but the H , decreased as the sintering temperature increased for the doped sample, while the crystallite size was smaller than that of the undoped sample revealed that La3+ ions had a fine effect on crystallite size. Meanwhile, the M , and H , for doped samples was less than those of the undoped sample suggested that the magnetic properties could be tailored further by the introduced La3+ ions.
References : [ 1 ] Bhise B V , Dongare M B , Patil S A , Sawant S R .
235
X-
ray infrared and magnetization studies on Mn substituted Ni-Zn femtes [ J ] . J. Mater. Sci. Lett., 1991, 10
(15): 922. [ 21 Abraham T. Economics of ceramic magnets [ J ] . A m . Cerum . SOC . Bull., 1994, 73(8) : 62. [ 31 Anil Kumar P S, Shrotri J J, Kulkami S D, Deshparide C E , Date S K. Low temperature synthesis of Nio.8ZQ.z Fe204 powder and its characterization [ J ] . Muter. Lett., 1996, 27(6): 293. [41 Mangalaraja R V , Ananthakumar S , Manohar P, Ganam F D. Initial permeability studies of Ni-Zn femtes prepared by flash combustion technique [ J ] . Mater . Sci . Eng. A , 2003, 355(1-2): 320.
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