NiFe2O4 ultrafine powder with high crystallinity has been prepared through a reverse microemulsion route. The composition in starting solution was optimized, and the resulting NiFe2O4 was formed at temperature of around 550–600 °C, which is much lower than that observed from the solid-state reaction. Magnetic investigation indicates that samples are soft magnetic materials with low coercivity and with the saturation magnetization close to the bulk value of Ni ferrite. © 2003 American Institute of Physics

Charles J. O’Connor

Chen D.-H.

Eun Young Shin

Gabriel Caruntu

Jinke Tang

Jiye Fang

John B. Wiley

Kevin L. Stokes

Le Duc Tung

Leonard Spinu

Narayan Shama

Shi Y.

Tomlinson W. J.

Wang J.

Xie Y.

NiFe2O4 ultrafine powder with high crystallinity has been prepared through a reverse microemulsion route. The composition in starting solution was optimized, and the resulting NiFe2O4 was formed at temperature of around 550–600 °C, which is much lower than that observed from the solid-state reaction. Magnetic investigation indicates that samples are soft-magnetic materials with low coercivity and with the saturation magnetization close to the bulk value of Ni ferrite

Fang, Jiye

Shama, Narayan

Tung, Le Duc

Shin, Eun Young

O\u27Connor, Charles J.

Stokes, Kevin L.

Caruntu, Gabriel

Wiley, John B

Spinu, Leonard

Tang, Jinke

ScholarWorks @ The University of New Orleans

University of New Orleans 
ScholarWorks@UNO 
Physics Faculty Publications Department of Physics 
2003 
Ultrafine NiFe2O4 powder fabricated from reverse microemulsion 
process 
Jiye Fang 
Narayan Shama 
Le Duc Tung 
Eun Young Shin 
Charles J. O'Connor 
University of New Orleans 
See next page for additional authors 
Follow this and additional works at: https://scholarworks.uno.edu/phys_facpubs 
 Part of the Materials Science and Engineering Commons, Nanoscience and Nanotechnology 
Commons, and the Physics Commons 
Recommended Citation 
J. Appl. Phys. 93, 7483 (2003) 
This Article is brought to you for free and open access by the Department of Physics at ScholarWorks@UNO. It has 
been accepted for inclusion in Physics Faculty Publications by an authorized administrator of ScholarWorks@UNO. 
For more information, please contact scholarworks@uno.edu. 
Authors 
Jiye Fang, Narayan Shama, Le Duc Tung, Eun Young Shin, Charles J. O'Connor, Kevin L. Stokes, Gabriel 
Caruntu, John B. Wiley, Leonard Spinu, and Jinke Tang 
This article is available at ScholarWorks@UNO: https://scholarworks.uno.edu/phys_facpubs/4 
Ultrafine NiFe2O4 powder fabricated from reverse microemulsion process
Jiye Fang,a) Narayan Shama, Le Duc Tung, Eun Young Shin, Charles J. O’Connor,
Kevin L. Stokes, Gabriel Caruntu, John B. Wiley, Leonard Spinu, and Jinke Tang
Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana 70148
~Presented on 13 November 2002!
NiFe2O4 ultrafine powder with high crystallinity has been prepared through a reverse
microemulsion route. The composition in starting solution was optimized, and the resulting NiFe2O4
was formed at temperature of around 550–600 °C, which is much lower than that observed from the
solid-state reaction. Magnetic investigation indicates that samples are soft-magnetic materials with
low coercivity and with the saturation magnetization close to the bulk value of Ni ferrite. © 2003
American Institute of Physics. @DOI: 10.1063/1.1555394#
I. INTRODUCTION
Magnetic ferrites are a group of technologically impor-
tant magnetic materials. Recent years, nanometer-sized mag-
netic ferrites have attracted considerable attention as their
physical properties are quite different from those of the
bulk.1,2 NiFe2O4 is a typical spin soft-magnetic ferrite and it
is extremely interesting to gain its ultrafine powder owing to
their broad applications3 such as microwave devices. Its
preparation by the classical solid-state reaction requires a
high calcination temperature and hence induces the sintering
and aggregation of particles.4 Although there has been a
number of reports demonstrating the achievements in wet
chemically preparing the NiFe2O4 nanoparticles through
kinds of approaches such as coprecipitation,5 sol–gel,6 and
hydrothermal7 methods, it is still worth improving the par-
ticles morphology and enhancing the crystallinity at a low
calcination temperature. In this work, we applied a reverse
microemulsion technique to the fabrication of NiFe2O4
nanoparticles.
II. EXPERIMENT
The starting materials include Ni(NO3)26H2O
~.99.999%!, cyclohexane ~99.91%!, poly (oxyethylene)9
nonyl phenol ether ~hereafter NP9!, all of these chemicals
were from Aldrich, U.S.; Fe(NO3)39H2O ~.99.3%, J. T.
Baker!, ammonium hydroxide ~GR, 28-30%, EM!, poly
(oxyethylene)x nonyl phenol ether ~hereafter NPx, x55 or 9,
from Albright and Wilson Asia Pte Ltd., Singapore!.
The procedure of establishing a partial phase diagram at
room temperature for the ternary system consisting of cyclo-
hexane, NP51NP9, and an aqueous solution has been de-
tailed elsewhere.8 To locate the determination between the
microemulsion and nonmicroemulsion regions, the aqueous
phase was titrated into a mixture of given cyclohexane to
surfactant ratio. Thorough mixing of the three components
was achieved using a Vortex mixer. Microemulsion compo-
sitions appear optically transparent when the size of aqueous
droplets is in the range of 5 to 20 nm, due to the fact that the
nanosized aqueous droplets do not cause a substantial degree
of light scattering. A series of such demarcation points were
obtained by varying the cyclohexane to surfactant ratio. Par-
tial phase diagrams at room temperature for three ternary
systems were thus established. They consisted of cyclohex-
ane, NP51NP9 ~weight ratio: 2:1! and an aqueous phase
containing 2.0 M ammonia or @x#M Ni(NO3)2
10.10 M Fe(NO3)3 ~x varies from 0.05 to 0.20!, respec-
tively.
The general procedure of powder preparation can be re-
ferred to Ref. 8. Two microemulsion compositions were pre-
pared. They all consisted of 67.5 wt % cyclohexane, 22.5
wt % NP5/NP9 ~weight ratio: 2:1!, and 10.0 wt % aqueous
solution. The aqueous phase contained either 2.0 M ammonia
solution, or @x#M Ni(NO3)210.10 M Fe(NO3)3 solution.
The concentration ‘‘x’’ was varied from 0.05 to 0.20 to opti-
mize the composition in the final NiFe2O4 powder. In each
time, the reaction was brought about by mixing the two com-
positions together via vigorously stirring for more than 20
min. To retrieve the precipitates formed in microemulsions,
the cyclohexane and surfactant were washed off using etha-
nol ~99.5%!, followed by recovery using centrifugation.
Samples were dried under a vacuum at room temperature for
at least 20 h.
The as-dried Ni–Fe-precursors with different Ni–Fe ra-
tios were characterized using a thermogravimetric analysis
~TGA! ~TA Instrument, SDT Q600! at a heating rate of
10 °C/min in air. They were then calcined in air at various
temperatures up to 900 °C, followed by phase analysis em-
ploying an x-ray diffraction ~XRD! technique ~Cu Ka , Phil-
ips X’pert-systems!. Composition ratio between Ni and Fe in
the calcined powders was determined based on the relative
intensities of major XRD peaks of NiO, Fe2O3 , and
NiFe2O4 . Crystallite size in single phase of NiFe2O4 was
estimated on the basis of line broadening at half maximum of
the ~311! peak. An NiFe2O4 particle image was taken from
JEOL 2010 transmission electron microscope. Magnetic
properties measurement was conducted using a supercon-
ducting quantum interference device magnetometer
~MPMS-5S Susceptometer from Quantum Design!.
a!Author to whom correspondence should be addressed; electronic mail:
jfang1@uno.edu
JOURNAL OF APPLIED PHYSICS VOLUME 93, NUMBER 10 15 MAY 2003
74830021-8979/2003/93(10)/7483/3/$20.00 © 2003 American Institute of Physics
Downloaded 31 Mar 2011 to 137.30.164.181. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions
III. RESULTS AND DISCUSSION
A. Formation of NiFe2O4 precursors
A coprecipitation between (Ni21/Fe31) and excessive
ammonia solution was involved in this preparation. Due to
the possible complexing interaction between the Ni21 and
OH2 during the coprecipitation, the stoichiometric ratio be-
tween the starting reagent Ni21 and Fe31 ~i.e., 1:2 in mol! is
not applicable. As to be mentioned later, we actually varied
the concentration of reagent Ni21 from 0.05 to 0.20 M when
that of Fe31 was fixed as 0.10 M. The ideal concentration of
Ni21 was thus optimized by considering the XRD-
determined phase ratio in those of calcined Ni–Fe oxides as
a feedback. The investigation was organized as illustrated in
Fig. 1.
To ensure that all the chemical preparations were ‘‘trans-
ferred’’ into the ‘‘nanoenvironment’’ in a medium of micro-
emulsions, we have partially established the cyclohexane—
~NP5/NP9 surfactant!—~aqueous solution! ternary phase
diagrams for all the systems containing 2.0 M ammonia so-
lution or various @x#M Ni(NO3)210.10 M Fe(NO3)3 solu-
tions. Figure 2 shows a typical partial ternary phase diagram
established at room temperature. The shaded region repre-
sents a reverse microemulsion area. Depending on the ratio
between Ni21 and Fe31 in the starting reagents, the final
Ni–Fe oxides may contain either single phase of NiFe2O4 ,
or NiFe2O41Fe2O3 , or NiFe2O41NiO or other possible
compositions. We have carefully examined various XRD pat-
terns derived from @x#M Ni(NO3)210.10 M Fe(NO3)3 so-
lutions in which the x volume was set as 0.05, 0.10, 0.12,
0.15, and 0.20. By analyzing these XRD patterns, x was op-
timized as 0.12. In other words, a starting solution containing
@0.12 M Ni(NO3)210.10 M Fe(NO3)3# gave a single phase
of NiFe2O4 under present synthetic conditions. Figure 3
shows the TGA trace at a heating rate of 10 °C/min in air for
precursors prepared using such composition. It exhibited
three apparent falls in specimen weight over the temperature
ranges from 40 to 180 °C, from 230 to 310 °C, and from 400
to 555 °C. The weight loss covering the first two falls, i.e., at
temperatures below 310 °C is believed to be due to the elimi-
nation of the residual water and the dehydration of the hy-
droxides hydrates in the precursors.9 The fall in specimen
weight over the temperature range from 400 to 555 °C is
related to the decomposition of nickel hydroxides and iron
hydroxides, as well as the residues of surfactant. As shown in
Fig. 3, the weight loss stops from ;555 °C, indicating the
complete formation of NiFe2O4 at that temperature.
B. NiFe2O4 powder characterization
Figure 4 is the XRD pattern recorded at room tempera-
ture from the precursor prepared using above composition
(x50.12) and calcined at 600 °C for 3 h. These peaks are
indexed to the cubic NiFe2O4 phase according to the stan-
dard ICDD PDF ~Card No. 10-0325!. From the XRD line
broadening of the ~311! peak using the Scherrer equation,10
the crystalline sizes were estimated as 11.2 nm, 16.9 nm, and
28.8 nm for the specimens calcined for 3 h at 600 °C, 700 °C,
and 800 °C, respectively. These results are in good agreement
with those characterized using transmission electron micros-
copy ~TEM! techniques. As demonstrated in Fig. 5, the TEM
image of powder calcined at 600 °C for 3 h reveals that the
discrete particles exist in polyhedron and average crystallite
size ranges around 10–15 nm in diameter with high crystal-
linity ~shown on the top inset!. Although both the XRD pat-
FIG. 1. Flow chart for the investigation of NiFe2O4 .
FIG. 2. The partial phase diagram established at room temperature for the
ternary system consisting of cyclohexane, NP5/NP9 ~weight ratio: 2:1! and
aqueous solution of @0.12 M Ni(NO3)210.10 M Fe(NO3)3# .
FIG. 3. TGA trace of N–Fe-hydroxides derived from two microemulsions
containing @0.12 M Ni(NO3)210.10 M Fe(NO3)3# and 2.0 M ammonia so-
lution. Sample was heated in air in a rate of 10 °C/min.
7484 J. Appl. Phys., Vol. 93, No. 10, Parts 2 & 3, 15 May 2003 Fang et al.
Downloaded 31 Mar 2011 to 137.30.164.181. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions
tern recorded from the sample calcined at 550 °C for 3 h and
the TGA curve indicate that NiFe2O4 could be formed at
550 °C, we still claim 600 °C as the formation temperature
because the sample calcined at 550 °C exhibits a relatively
low saturation magnetization ~43.0 emu/g! when measured at
300 K. This may indicate that at 550 °C the sample may still
contains a small amount of amorphous impurities, which is
undetectable by XRD and TGA. It is worth mentioning the
formation temperature of 600 °C is much lower than that
observed from the solid-state reaction.11
Figure 6 shows the hysteresis loops of NiFe2O4 powder
calcined for 3 h at 600 °C @Fig. 6~a!# and 800 °C @Fig. 6~b!#.
Both samples present soft-magnetic behaviors with coerciv-
ity less than 350 Oe at 5 K ~see the insets of Fig. 6!. For
sample calcined at 800 °C, we obtained saturation magneti-
zation of 54.5 emu/g, which is very close to the bulk value of
55 emu/g reported for NiFe2O4 .12 For sample calcined at
600 °C, the magnetization measured at 5 K and 300 K still
increases slightly with increasing magnetic field up to 50
kOe. At the maximum field of 50 kOe, we obtained value of
magnetization being only 46.9 emu/g at 300 K. This behav-
ior is believed to be associated with superparamagnetism, as
the particle of ,15 nm is close to the critical size of super-
paramagnetism for NiFe2O4 . When increasing the particle
size by elevating the calcinations temperature, this phenom-
enon becomes unapparent and even vanished.
ACKNOWLEDGMENT
This work was supported by the L.A. Board of Regents,
NSF/LEQSF ~2001-04!-RII-03 and the Air Force, F49620-
02-C-0060.
1 G. A. Ozin, Adv. Mater. 4, 612 ~1992!.
2 H. Gleiter, Adv. Mater. 4, 474 ~1992!.
3 Z. H. Zhou, J. M. Xue, J. Wang, H. S. O. Chan, T. Yu, and Z. X. Shen, J.
Appl. Phys. 91, 6015 ~2002!.
4 G. Economos, J. Am. Ceram. Soc. 42, 628 ~1959!.
5 Y. Shi, J. Ding, X. Liu, and J. Wang, J. Magn. Magn. Mater. 205, 249
~1999!.
6 D.-H. Chen and X.-R. He, Mater. Res. Bull. 36, 1369 ~2001!.
7 Y. Xie, Y. Qian, J. Li, Z. Chen, and L. Yang, Mater. Sci. Eng., B 34, L1
~1995!.
8 J. Wang, J. Fang, S.-C. Ng, L.-M. Gan, C.-H. Chew, X. Wang, and Z.
Shen, J. Am. Ceram. Soc. 82, 873 ~1999!.
9 Y. Ohara, K. Koumoto, T. Shimizu, and H. Yanagida, J. Mater. Sci. 30,
263 ~1995!; D. L. Perry and S. L. Phillips ~Ed.!, Handbook of Inorganic
Compounds ~CRC Press, Boca Raton, 1995!, p. 216.
10 H. P. Klug and L. E. Alexander ~ed.!, X-ray Diffraction Procedures for
Polycrystalline and Amorphous Materials ~Wiley, New York, 1954!.
11 W. J. Tomlinson and J. Lilley, J. Mater. Sci. 13, 1148 ~1978!.
12 J. Smit and H. P. Wijin, Ferrites ~Philips Technical Library, Eindhoven,
The Netherlands, 1959!, p. 157.
FIG. 4. XRD trace of NiFe2O4 , which was prepared from microemulsions
containing @0.12 M Ni(NO3)210.10 M Fe(NO3)3# solution and was cal-
cined at 600 °C for 3 h.
FIG. 6. The hysteresis loops of NiFe2O4 measured at 300 K and 5 K. ~a!
Sample calcined at 600 °C for 3 h and ~b! sample calcined at 800 °C for 3 h.
FIG. 5. TEM images of microemulsion-derived NiFe2O4 ~calcined at
600 °C for 3 h!.
7485J. Appl. Phys., Vol. 93, No. 10, Parts 2 & 3, 15 May 2003 Fang et al.
Downloaded 31 Mar 2011 to 137.30.164.181. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions


English

Ultrafine NiFe2O4 powder fabricated from reverse microemulsion process

University of New Orleans

University of New Orleans ScholarWorks@UNO Physics Faculty Publications Department of Physics 2003 Ultrafine NiFe2O4 powder fabricated from reverse microemulsion process Jiye Fang Narayan Shama Le Duc Tung Eun Young Shin Charles J. O'Connor University of New Orleans See next page for additional authors Follow this and additional works at: https://scholarworks.uno.edu/phys_facpubs  Part of the Materials Science and Engineering Commons, Nanoscience and Nanotechnology Commons, and the Physics Commons Recommended Citation J. Appl. Phys. 93, 7483 (2003) This Article is brought to you for free and open access by the Department of Physics at ScholarWorks@UNO. It has been accepted for inclusion in Physics Faculty Publications by an authorized administrator of ScholarWorks@UNO. For more information, please contact scholarworks@uno.edu. Authors Jiye Fang, Narayan Shama, Le Duc Tung, Eun Young Shin, Charles J. O'Connor, Kevin L. Stokes, Gabriel Caruntu, John B. Wiley, Leonard Spinu, and Jinke Tang This article is available at ScholarWorks@UNO: https://scholarworks.uno.edu/phys_facpubs/4 Ultrafine NiFe2O4 powder fabricated from reverse microemulsion processJiye Fang,a) Narayan Shama, Le Duc Tung, Eun Young Shin, Charles J. O’Connor,Kevin L. Stokes, Gabriel Caruntu, John B. Wiley, Leonard Spinu, and Jinke TangAdvanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana 70148~Presented on 13 November 2002!NiFe2O4 ultrafine powder with high crystallinity has been prepared through a reversemicroemulsion route. The composition in starting solution was optimized, and the resulting NiFe2O4was formed at temperature of around 550–600 °C, which is much lower than that observed from thesolid-state reaction. Magnetic investigation indicates that samples are soft-magnetic materials withlow coercivity and with the saturation magnetization close to the bulk value of Ni ferrite. © 2003American Institute of Physics. @DOI: 10.1063/1.1555394#I. INTRODUCTIONMagnetic ferrites are a group of technologically impor-tant magnetic materials. Recent years, nanometer-sized mag-netic ferrites have attracted considerable attention as theirphysical properties are quite different from those of thebulk.1,2 NiFe2O4 is a typical spin soft-magnetic ferrite and itis extremely interesting to gain its ultrafine powder owing totheir broad applications3 such as microwave devices. Itspreparation by the classical solid-state reaction requires ahigh calcination temperature and hence induces the sinteringand aggregation of particles.4 Although there has been anumber of reports demonstrating the achievements in wetchemically preparing the NiFe2O4 nanoparticles throughkinds of approaches such as coprecipitation,5 sol–gel,6 andhydrothermal7 methods, it is still worth improving the par-ticles morphology and enhancing the crystallinity at a lowcalcination temperature. In this work, we applied a reversemicroemulsion technique to the fabrication of NiFe2O4nanoparticles.II. EXPERIMENTThe starting materials include Ni(NO3)26H2O~.99.999%!, cyclohexane ~99.91%!, poly (oxyethylene)9nonyl phenol ether ~hereafter NP9!, all of these chemicalswere from Aldrich, U.S.; Fe(NO3)39H2O ~.99.3%, J. T.Baker!, ammonium hydroxide ~GR, 28-30%, EM!, poly(oxyethylene)x nonyl phenol ether ~hereafter NPx, x55 or 9,from Albright and Wilson Asia Pte Ltd., Singapore!.The procedure of establishing a partial phase diagram atroom temperature for the ternary system consisting of cyclo-hexane, NP51NP9, and an aqueous solution has been de-tailed elsewhere.8 To locate the determination between themicroemulsion and nonmicroemulsion regions, the aqueousphase was titrated into a mixture of given cyclohexane tosurfactant ratio. Thorough mixing of the three componentswas achieved using a Vortex mixer. Microemulsion compo-sitions appear optically transparent when the size of aqueousdroplets is in the range of 5 to 20 nm, due to the fact that thenanosized aqueous droplets do not cause a substantial degreeof light scattering. A series of such demarcation points wereobtained by varying the cyclohexane to surfactant ratio. Par-tial phase diagrams at room temperature for three ternarysystems were thus established. They consisted of cyclohex-ane, NP51NP9 ~weight ratio: 2:1! and an aqueous phasecontaining 2.0 M ammonia or @x#M Ni(NO3)210.10 M Fe(NO3)3 ~x varies from 0.05 to 0.20!, respec-tively.The general procedure of powder preparation can be re-ferred to Ref. 8. Two microemulsion compositions were pre-pared. They all consisted of 67.5 wt % cyclohexane, 22.5wt % NP5/NP9 ~weight ratio: 2:1!, and 10.0 wt % aqueoussolution. The aqueous phase contained either 2.0 M ammoniasolution, or @x#M Ni(NO3)210.10 M Fe(NO3)3 solution.The concentration ‘‘x’’ was varied from 0.05 to 0.20 to opti-mize the composition in the final NiFe2O4 powder. In eachtime, the reaction was brought about by mixing the two com-positions together via vigorously stirring for more than 20min. To retrieve the precipitates formed in microemulsions,the cyclohexane and surfactant were washed off using etha-nol ~99.5%!, followed by recovery using centrifugation.Samples were dried under a vacuum at room temperature forat least 20 h.The as-dried Ni–Fe-precursors with different Ni–Fe ra-tios were characterized using a thermogravimetric analysis~TGA! ~TA Instrument, SDT Q600! at a heating rate of10 °C/min in air. They were then calcined in air at varioustemperatures up to 900 °C, followed by phase analysis em-ploying an x-ray diffraction ~XRD! technique ~Cu Ka , Phil-ips X’pert-systems!. Composition ratio between Ni and Fe inthe calcined powders was determined based on the relativeintensities of major XRD peaks of NiO, Fe2O3 , andNiFe2O4 . Crystallite size in single phase of NiFe2O4 wasestimated on the basis of line broadening at half maximum ofthe ~311! peak. An NiFe2O4 particle image was taken fromJEOL 2010 transmission electron microscope. Magneticproperties measurement was conducted using a supercon-ducting quantum interference device magnetometer~MPMS-5S Susceptometer from Quantum Design!.a!Author to whom correspondence should be addressed; electronic mail:jfang1@uno.eduJOURNAL OF APPLIED PHYSICS VOLUME 93, NUMBER 10 15 MAY 200374830021-8979/2003/93(10)/7483/3/$20.00 © 2003 American Institute of PhysicsDownloaded 31 Mar 2011 to 137.30.164.181. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissionsIII. RESULTS AND DISCUSSIONA. Formation of NiFe2O4 precursorsA coprecipitation between (Ni21/Fe31) and excessiveammonia solution was involved in this preparation. Due tothe possible complexing interaction between the Ni21 andOH2 during the coprecipitation, the stoichiometric ratio be-tween the starting reagent Ni21 and Fe31 ~i.e., 1:2 in mol! isnot applicable. As to be mentioned later, we actually variedthe concentration of reagent Ni21 from 0.05 to 0.20 M whenthat of Fe31 was fixed as 0.10 M. The ideal concentration ofNi21 was thus optimized by considering the XRD-determined phase ratio in those of calcined Ni–Fe oxides asa feedback. The investigation was organized as illustrated inFig. 1.To ensure that all the chemical preparations were ‘‘trans-ferred’’ into the ‘‘nanoenvironment’’ in a medium of micro-emulsions, we have partially established the cyclohexane—~NP5/NP9 surfactant!—~aqueous solution! ternary phasediagrams for all the systems containing 2.0 M ammonia so-lution or various @x#M Ni(NO3)210.10 M Fe(NO3)3 solu-tions. Figure 2 shows a typical partial ternary phase diagramestablished at room temperature. The shaded region repre-sents a reverse microemulsion area. Depending on the ratiobetween Ni21 and Fe31 in the starting reagents, the finalNi–Fe oxides may contain either single phase of NiFe2O4 ,or NiFe2O41Fe2O3 , or NiFe2O41NiO or other possiblecompositions. We have carefully examined various XRD pat-terns derived from @x#M Ni(NO3)210.10 M Fe(NO3)3 so-lutions in which the x volume was set as 0.05, 0.10, 0.12,0.15, and 0.20. By analyzing these XRD patterns, x was op-timized as 0.12. In other words, a starting solution containing@0.12 M Ni(NO3)210.10 M Fe(NO3)3# gave a single phaseof NiFe2O4 under present synthetic conditions. Figure 3shows the TGA trace at a heating rate of 10 °C/min in air forprecursors prepared using such composition. It exhibitedthree apparent falls in specimen weight over the temperatureranges from 40 to 180 °C, from 230 to 310 °C, and from 400to 555 °C. The weight loss covering the first two falls, i.e., attemperatures below 310 °C is believed to be due to the elimi-nation of the residual water and the dehydration of the hy-droxides hydrates in the precursors.9 The fall in specimenweight over the temperature range from 400 to 555 °C isrelated to the decomposition of nickel hydroxides and ironhydroxides, as well as the residues of surfactant. As shown inFig. 3, the weight loss stops from ;555 °C, indicating thecomplete formation of NiFe2O4 at that temperature.B. NiFe2O4 powder characterizationFigure 4 is the XRD pattern recorded at room tempera-ture from the precursor prepared using above composition(x50.12) and calcined at 600 °C for 3 h. These peaks areindexed to the cubic NiFe2O4 phase according to the stan-dard ICDD PDF ~Card No. 10-0325!. From the XRD linebroadening of the ~311! peak using the Scherrer equation,10the crystalline sizes were estimated as 11.2 nm, 16.9 nm, and28.8 nm for the specimens calcined for 3 h at 600 °C, 700 °C,and 800 °C, respectively. These results are in good agreementwith those characterized using transmission electron micros-copy ~TEM! techniques. As demonstrated in Fig. 5, the TEMimage of powder calcined at 600 °C for 3 h reveals that thediscrete particles exist in polyhedron and average crystallitesize ranges around 10–15 nm in diameter with high crystal-linity ~shown on the top inset!. Although both the XRD pat-FIG. 1. Flow chart for the investigation of NiFe2O4 .FIG. 2. The partial phase diagram established at room temperature for theternary system consisting of cyclohexane, NP5/NP9 ~weight ratio: 2:1! andaqueous solution of @0.12 M Ni(NO3)210.10 M Fe(NO3)3# .FIG. 3. TGA trace of N–Fe-hydroxides derived from two microemulsionscontaining @0.12 M Ni(NO3)210.10 M Fe(NO3)3# and 2.0 M ammonia so-lution. Sample was heated in air in a rate of 10 °C/min.7484 J. Appl. Phys., Vol. 93, No. 10, Parts 2 & 3, 15 May 2003 Fang et al.Downloaded 31 Mar 2011 to 137.30.164.181. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissionstern recorded from the sample calcined at 550 °C for 3 h andthe TGA curve indicate that NiFe2O4 could be formed at550 °C, we still claim 600 °C as the formation temperaturebecause the sample calcined at 550 °C exhibits a relativelylow saturation magnetization ~43.0 emu/g! when measured at300 K. This may indicate that at 550 °C the sample may stillcontains a small amount of amorphous impurities, which isundetectable by XRD and TGA. It is worth mentioning theformation temperature of 600 °C is much lower than thatobserved from the solid-state reaction.11Figure 6 shows the hysteresis loops of NiFe2O4 powdercalcined for 3 h at 600 °C @Fig. 6~a!# and 800 °C @Fig. 6~b!#.Both samples present soft-magnetic behaviors with coerciv-ity less than 350 Oe at 5 K ~see the insets of Fig. 6!. Forsample calcined at 800 °C, we obtained saturation magneti-zation of 54.5 emu/g, which is very close to the bulk value of55 emu/g reported for NiFe2O4 .12 For sample calcined at600 °C, the magnetization measured at 5 K and 300 K stillincreases slightly with increasing magnetic field up to 50kOe. At the maximum field of 50 kOe, we obtained value ofmagnetization being only 46.9 emu/g at 300 K. This behav-ior is believed to be associated with superparamagnetism, asthe particle of ,15 nm is close to the critical size of super-paramagnetism for NiFe2O4 . When increasing the particlesize by elevating the calcinations temperature, this phenom-enon becomes unapparent and even vanished.ACKNOWLEDGMENTThis work was supported by the L.A. Board of Regents,NSF/LEQSF ~2001-04!-RII-03 and the Air Force, F49620-02-C-0060.1 G. A. Ozin, Adv. Mater. 4, 612 ~1992!.2 H. Gleiter, Adv. Mater. 4, 474 ~1992!.3 Z. H. Zhou, J. M. Xue, J. Wang, H. S. O. Chan, T. Yu, and Z. X. Shen, J.Appl. Phys. 91, 6015 ~2002!.4 G. Economos, J. Am. Ceram. Soc. 42, 628 ~1959!.5 Y. Shi, J. Ding, X. Liu, and J. Wang, J. Magn. Magn. Mater. 205, 249~1999!.6 D.-H. Chen and X.-R. He, Mater. Res. Bull. 36, 1369 ~2001!.7 Y. Xie, Y. Qian, J. Li, Z. Chen, and L. Yang, Mater. Sci. Eng., B 34, L1~1995!.8 J. Wang, J. Fang, S.-C. Ng, L.-M. Gan, C.-H. Chew, X. Wang, and Z.Shen, J. Am. Ceram. Soc. 82, 873 ~1999!.9 Y. Ohara, K. Koumoto, T. Shimizu, and H. Yanagida, J. Mater. Sci. 30,263 ~1995!; D. L. Perry and S. L. Phillips ~Ed.!, Handbook of InorganicCompounds ~CRC Press, Boca Raton, 1995!, p. 216.10 H. P. Klug and L. E. Alexander ~ed.!, X-ray Diffraction Procedures forPolycrystalline and Amorphous Materials ~Wiley, New York, 1954!.11 W. J. Tomlinson and J. Lilley, J. Mater. Sci. 13, 1148 ~1978!.12 J. Smit and H. P. Wijin, Ferrites ~Philips Technical Library, Eindhoven,The Netherlands, 1959!, p. 157.FIG. 4. XRD trace of NiFe2O4 , which was prepared from microemulsionscontaining @0.12 M Ni(NO3)210.10 M Fe(NO3)3# solution and was cal-cined at 600 °C for 3 h.FIG. 6. The hysteresis loops of NiFe2O4 measured at 300 K and 5 K. ~a!Sample calcined at 600 °C for 3 h and ~b! sample calcined at 800 °C for 3 h.FIG. 5. TEM images of microemulsion-derived NiFe2O4 ~calcined at600 °C for 3 h!.7485J. Appl. Phys., Vol. 93, No. 10, Parts 2 & 3, 15 May 2003 Fang et al.Downloaded 31 Mar 2011 to 137.30.164.181. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions

NiFe2O4 ultrafine powder with high crystallinity has been prepared through a reverse microemulsion route. The composition in starting solution was optimized, and the resulting NiFe2O4 was formed at temperature of around 550–600 °C, which is much lower than that observed from the solid-state reaction. Magnetic investigation indicates that samples are soft magnetic materials with low coercivity and with the saturation magnetization close to the bulk value of Ni ferrite

Jiye Fang (1661452)

Narayan Shama (10061761)

Le Duc Tung (10061383)

Eun Young Shin (5750741)

Charles J. O’Connor (1910260)

Kevin L. Stokes (2144260)

Gabriel Caruntu (1731379)

John B. Wiley (1405783)

Leonard Spinu (1901704)

Jinke Tang (2056753)

The Francis Crick Institute

O’Connor, Charles J.

Wiley, John B.

University of Wyoming

Ultrafine NiFe 2 O 4 powder fabricated from reverse microemulsion process

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https://scholarworks.uno.edu/cgi/viewcontent.cgi?article=1003&amp;context=phys_facpubs

Ultrafine NiFe2O4 powder fabricated from reverse microemulsion process

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