Ad ances in Na u al Sciences:
Nanoscience and Nano echnology
PAPER • OPEN ACCESS
Impac o g ain size and s uc u al changes on
magne ic, dielec ic, elec ical, impedance and
modulus spec oscopic cha ac e is ics o CoFe2O4
nanopa icles syn hesized by honey media ed sol-
gel combus ion me hod
To ci e his a icle: Ragh end a Singh Yada e al 2017 Ad . Na . Sci: Nanosci. Nano echnol. 8
045002
View he a icle online o upda es and enhancemen s.
Rela ed con en
S udies on s uc u al, op ical and magne ic
p ope ies o cobal subs i u ed magne i e
luids (CoxFe1xFe2O4)
Blessy Babuku y, Nandakuma Kala ikkal
and Swapna S Nai
-
E ec o Mn2+ doping and SiO2 coa ing
on magne o-op ical p ope ies o CoFe2O4
nano-pa icles
Kamal R Awad, M M S Wahsh, A G M
O hman e al.
-
In luence o Ra e Ea h (Gd3+) on
S uc u al, Gigahe z Dielec ic and
Magne ic S udies o Cobal e i e
E um Pe aiz and I H Gul
-
This con en was downloaded om IP add ess 195.178.95.132 on 29/06/2018 a 13:36
1 © 2017 Vie nam Academy o Science & Technology
Ragh end aSinghYada 1, I oKuři ka1, Ja milaVilcako a1,
Ja omi Ha lica2, Ji iMasilko2, LukasKalina2, JakubTkacz2, JiříŠ ec2,
Voj ěchEne 2 and Mi osla aHajdúcho á2
1 Cen e o Polyme Sys ems, Uni e si y Ins i u e, Tomas Ba a Uni e si y in Zlín, T ida Tomase Ba i
5678, 760 01 Zlín, Czechia
2 Ma e ials Resea ch Cen e, B no Uni e si y o Technology, Pu kyňo a 464/118, 61200 B no, Czechia
E-mail: yada[email p o ec ed].cz
Recei ed 9 Feb ua y 2017
Accep ed o publica ion 26 July 2017
Published 29 Augus 2017
Abs ac
In his wo k CoFe2O4 spinel e i e nanopa icles we e syn hesized by honey media ed sol-gel
combus ion me hod and u he annealed a highe empe a u e 500 °C, 700 °C, 900 °C and
1100 °C. The syn hesized spinel e i e nanopa icles is in es iga ed by x- ay di ac ion,
Raman spec oscopy, Fou ie ans o m in a ed (FTIR) spec oscopy, he mog a ime ic
analysis/di e en ial scanning calo ime y (TGA/DSC), ield emission scanning elec on
mic oscopy, x- ay pho oelec on spec oscopy and ib a ing sample magne ome e . The x- ay
di ac ion s udy e eals ace-cen e ed cubic spinel cobal e i e c ys al phase o ma ion. The
c ys alli e size and la ice pa ame e a e inc eased wi h annealing empe a u e. Raman and
Fou ie ans o m in a ed spec a also con i m spinel e i e c ys al s uc u e o syn hesized
nanopa icles. The exis ence o ca ion a oc ahed al and e ahed al si e in cobal e i e
nanopa icles is con i med by x- ay pho oelec on spec oscopy. Magne ic measu emen shows
inc eased sa u a ion magne iza ion 74.4 emu g−1 a highe annealing empe a u e 1100 °C,
high coe ci i y 1347.3 Oe a lowe annealing empe a u e 500 °C, and high emanen
magne iza ion 32.3 emu g−1 a 900 °C annealing empe a u e. The magne ic p ope ies
o syn hesized e i e nanopa icles can be uned by adjus ing sizes h ough annealing
empe a u e. Fu he mo e, he dielec ic cons an and ac conduc i i y shows a ia ion wi h
equency (1–107 Hz), g ain size and ca ion edis ibu ion. The modulus spec oscopy s udy
e eals he ole o bulk g ain and g ain bounda y owa ds he esis ance and capaci ance. The
cole-cole plo s in modulus o malism also well suppo he elec ical esponse o nanopa icles
o igina ed om bo h g ain and g ain bounda ies. The dielec ic, elec ical, magne ic,
impedance and modulus spec oscopic cha ac e is ics o syn hesized CoFe2O4 spinel e i e
Ad ances in Na u al Sciences: Nanoscience and Nano echnology
Impac o g ain size and s uc u al
changes on magne ic, dielec ic, elec ical,
impedance and modulus spec oscopic
cha ac e is ics o CoFe2O4 nanopa icles
syn hesized by honey media ed sol-gel
combus ion me hod
R S Yada e al
045002
ANSNCK
© 2017 Vie nam Academy o Science & Technology
8
Ad . Na . Sci.: Nanosci. Nano echnol.
ANSN
2043-6254
10.1088/2043-6254/aa853a
Pape
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Ad ances in Na u al Sciences: Nanoscience and Nano echnology
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dis ibu ion o his wo k mus main ain a ibu ion o he au ho (s) and he i le
o he wo k, jou nal ci a ion and DOI.
2017
2043-6254/17/045002+14$33.00
h ps://doi.o g/10.1088/2043-6254/aa853a
Ad . Na . Sci.: Nanosci. Nano echnol. 8 (2017) 045002 (14pp)
R S Yada e al
2
nanopa icles demons a e he applicabili y o hese nanopa icles o magne ic eco ding,
memo y de ices and o mic owa e applica ions.
Keywo ds: spinel e i e, nanopa icles, g een syn hesis, magne ic p ope y, dielec ic p ope y
Classi ica ion numbe s: 2.03, 4.02, 5.02
1. In oduc ion
Recen ly, spinel e i e nanopa icles ha e been ex ensi ely
s udied due o i s in e es ing p ope ies o a ious applica ions
[1–3]. Among he spinel e i es, CoFe2O4 is an a ac i e ma -
e ial due o i s app ecia ed p ope ies such as high coe ci i y,
mode a e sa u a ion magne iza ion, la ge magne oc ys alline
aniso opy, high elec ical esis i i y, high magne os ic i e
coe icien , good mechanical ha dness and chemical s abili y
[4, 5]. I has echnological po en ial applica ions in high den-
si y eco ding sys ems, mic owa e abso be s, a ge ed d ug
deli e y sys ems, magne ic esonance imaging con as agen ,
high alue o he speci ic abso p ion a e o hype he mia
ea men , cell sepa a ion and de ec ion, ca alys o wa e
spli ing, emo al o hea y me als om was e wa e , magne ic
swi ches, chemical senso s, s ess and non-con ac o que sen-
so s, e c [6–13]. The p ope ies o spinel e i e nanopa icles
a e highly sensi i e o he a ious ac o s such as p epa a ion
echniques, pa icle size, mo phology, annealing empe a u e
and ca ion dis ibu ion a e ahed al and oc ahed al si es. Bulk
CoFe2O4 possesses an in e se spinel s uc u e wi h Co2+ ions
in oc ahed al si e and Fe3+ ions equally dis ibu ed be ween
e ahed al and oc ahed al si es. Howe e , nanosized CoFe2O4
e i e nanopa icles exhibi ca ionic in e sion and pe cen age
o p esence o Co2+ and Fe3+ ions a bo h si es depends on he
me hod o p epa a ion o spinel e i e nanopa icles [14]. The
p edominan supe exchange in e ac ion be ween he ca ions a
e ahed al and oc ahed al si es ia oxygen ions in luences he
magne ic p ope ies o spinel e i e [15].
In he las decade, spinel e i e nanos uc u es ha e been
syn hesized by a ious chemical syn hesis me hods such as
sol-gel, co-p ecipi a ion, hyd o he mal, sol o he mal, sono-
chemical me hod, elec ochemical, e e se micelles [16–21].
Nowadays, he e is a g ea need o de elop simple, cos -
e ec i e and en i onmen iendly me hods o p oduc ion o
spinel e i e nanopa icles. Recen ly, biosyn hesis is an al e -
na i e syn hesis echnique o syn hesize spinel e i e nano-
pa icles. Laokul e al [22] demons a ed he use o a simple
syn he ic me hod using cheap p ecu so s o aloe e a plan
ex ac which p o ides high-yield nanosized e i es wi h
well c ys alline s uc u e and accep able magne ic p ope ies,
and he me hod is expec ed o p epa e nanoc ys alline oxides
o o he in e es ing ma e ials. Phumying e al [23] epo ed
syn hesis o e i e nanoc ys alline powde s using aloe e a
plan ex ac solu ion in hyd o he mal syn hesis echnique.
Mo eo e , Manikandan e  al [24] syn hesized e i e nano-
pa icles ia aloe e a plan ex ac using mic owa e combus-
ion me hod. Wongp a a e al [25] in es iga ed he e ec o
ca ions dis ibu ion on magne ic p ope ies o Co1−xNixFe2O4
(x = 0, 0.25,0.50, 0.75 and 1.0) nanopa icles syn hesized
by aloe e a ex ac solu ion assis ed hyd o he mal me hod.
Kombaiah e al [26] s udied he mic owa e assis ed and con-
en ional combus ion syn hesis o hibiscus osa-sinensis plan
ex ac based ZnFe2O4 nanopa icles and hei op ical and
magne ic p ope ies. The hibiscus osa-sinensis is an he ba-
ceous plan and he bio-chemical cons i uen s o his plan s
a e a axe ol ace a e, β-si os e ol, campes e ol, s igmas e ol,
choles e ol, e gos e ol, lipids, ci ic, a a ic and oxalic acids,
uc ose, glucose, suc ose, la onoids and la onoid gly-
cosides. Sun e  al [27] epo ed magne ic p ope ies o he
nanoc ys alline CoFe2O4 e i e hin ilms p epa ed by a no el
sol–gel me hod using glucose as an addi ional agen . Fu he ,
Tong e  al [28] de eloped a e sa ile glucose-enginee ed
p ecipi a ion–sin e ing p ocess o he selec i e and mass
p epa a ion o sponge-like e i e (M = Fe, Co, Zn, Ni, Mn)
mic o-polyhed a. In his esea ch g oup’s epo ed wo k, glu-
cose ac ed as a educ an , p o ec ing agen , s uc u e-di ec ing
agen and sac i icial empla e. Fu he mo e, ou esea ch
g oup also in es iga ed he e ec o s uc u al changes on
magne ic p ope ies o e i e nanopa icles ob ained using
s a ch in sol-gel combus ion syn hesis [29–31].
I is in e es ing o s udy o ma ion and p ope y o spinel e -
i e nanopa icles syn hesized ia a me hod media ed h ough
na u al sou ce o glucose and uc ose, i.e. honey. He ein,
we used a g een syn hesis ou e ia honey media ed sol-gel
au o-combus ion me hod o p epa e CoFe2O4 spinel e i e
nanopa icles. This is a no el way wi h a unique combina-
ion o biological species wi h an aqueous solu ion con aining
sal s o desi ed me als o sol-gel and sel -igni ing combus-
ion p ocess. The e m g een syn hesis is used since na u al
honey is used o syn hesis o e i e nanopa icles which ac
as gela ing and educing agen o uel o sol-gel au o-com-
bus ion syn hesis. Honey is swee iscous luid made by bees
and he majo cons i uen s o honey a e glucose and uc ose
[32]. The p esence o glucose and uc ose in na u al honey
ob iously plays a ole on he o ma ion o nanopa icles as
iscous medium, p o ec ing agen and na u al educ an . The
syn hesis o e i e nanopa icles using honey a oids he usage
o ha m ul and oxic educing agen in combus ion me hod.
The use o honey is an en i onmen ly iendly, simple and
e icien ou e o o ma ion o cobal e i e nanopa icles.
In he p esen wo k honey is used o syn hesis o CoFe2O4
spinel e i e nanopa icles. Fu he , he e ec o g ain size
and s uc u al changes on magne ic, dielec ic and elec ical
p ope ies a e in es iga ed. Fu he mo e, he de ailed s udy o
modulus and impedance spec oscopy is ca ied ou o e eal
he con ibu ion o g ain and g ain bounda y on elec ical
anspo mechanism and elaxa ion p ocess.
Ad . Na . Sci.: Nanosci. Nano echnol. 8 (2017) 045002
R S Yada e al
3
2. Expe imen al
2.1. Ma e ials and p epa a ion me hod
The nanopa icles o CoFe2O4 spinel e i e we e syn hesized
using honey media ed sel -p opaga ing sol-gel au o-com-
bus ion me hod. All he chemicals used in ou expe imen s,
Fe(NO3)3·9H2O, Co(NO3)2·6H2O we e o analy ical g ade
and we e pu chased om Al a Aesa GmbH & Co KG,
Ge many. Honey was p oduc o Aus alia, made by bees
ha o age on eucalyp us ees, packed in he UK o Tesco
S o es L d, Cheshun , EN8 9SL, UK. In a ypical syn hesis,
Co(NO3)2·6H2O (4.16 g) and Fe(NO3)3·9H2O (11.6 g) we e
dissol ed in dis illed wa e (150 ml) o ob ain a mixed solu-
ion. An aqueous solu ion (150 ml) o honey (10 g) was mixed
wi h he me al-ni a e solu ion. The mixed solu ion was placed
on a ho pla e wi h con inuous s i ing a 100 °C. Du ing e ap-
o a ion, he solu ion o med a e y iscous gel. Then he gel
was hea ed o 350 °C o ini ia e a sel -sus aining combus ion
eac ion and p oduce as-bu n e i e powde . The main con-
s i uen s o honey, i.e. glucose and uc ose a e ‘single’ suga s
o monosaccha ides. These monosaccha ides ha e he same
molecula o mula (C6H12O6), howe e , he a angemen o
a oms a e di e en in each case. When he me al-honey e i e
gel p ecu so was placed a empe a u e 350 °C, he decom-
posi ion o glucose and uc ose wi h elease o gases ni ogen
and ca bon dioxide occu ed and hen inal p oduc cobal
e i e powde s o med. The ollowing equa ion ep esen s
he decomposi ion o me al-honey e i e gel p ecu so s in o
cobal e i e:
Co(NO
3
)
2
·6H
2
O+2Fe(NO
3
)
3
·9H
2
O+2C
6
H
12
O
6
+2O2
∆
−→ CoFe2O4+4N2↑+27H2O↑+12CO2↑.
Finally, he as-p epa ed cobal e i e nanopa icles powde s
we e addi ionally annealed in a u nace in ai a mosphe e a
500 °C, 700 °C, 900 °C and 1100 °C, o 2 h, o achie e di -
e en nanosized e i e samples. The samples as p epa ed and
annealed a 500 °C, 700 °C, 900 °C, 1100 °C we e designa ed
as CoH, CoH5, CoH7, CoH9, CoH11, espec i ely.
2.2. Cha ac e iza ion echniques
The s uc u al cha ac e is ics o syn hesized cobal e i e
nanopa icles we e in es iga ed using PANaly ical Empy ean
x- ay di ac ome e wi h Cu-Kα adia ion (λ = 1.5406 Å).
Raman measu emen s we e pe o med using Nano inde -S,
SOLAR TII, L d, a 488 nm exci a ion wi h lase powe
13 mW wi h A + lase exci a ion sou ce o e he ange o
150–850 cm−1. Fou ie ans o m in a ed (FTIR) spec -
oscopy o e i e nanopa icles we e eco ded using Nicole
iS 50 FTIR spec ome e . The mo phology o he syn hesized
spinel e i e nanopa icles we e s udied using a ield emis-
sion scanning elec on mic oscope (FESEM) model JEOL
JSM-7600F, equipped wi h an ene gy dispe si e spec oscopy
(EDS) sys em. Magne ic hys e esis loops we e measu ed
using a ib a ing sample magne ome e (VSM 7407, Lake
Sho e) a oom empe a u e wi h maximum applied magne ic
ield o 10 kOe. The he mal analysis was ca ied ou using a
simul aneous he mog a ime ic and di e en ial he mal anal-
ysis (TG-DTA) sys em using TA Ins umen s Q600. Ca ion
dis ibu ion a oc ahed al and e ahed al si es and alence
s a es in samples we e in es iga ed by x- ay pho oelec on
spec oscopy (XPS) using K a os Analy ical Axis Ul a DLD.
The dielec ic cons an and dielec ic loss angen we e mea-
su ed in he equency ange 1–107 Hz a oom empe a u e
using a B oadband Dielec ic Impedance Analyze Concep
40 (No ocon ol, Ge many). The sample dimension o pelle
o e i e nanopa icles was 20 mm in diame e and 0.5 mm
in hickness. The complex impedance measu emen was ca -
ied ou wi h a s anda d sample cell BDS 1200 employing RC
model.
3. Resul and discussion
3.1. The mog a ime ic analysis/di e en ial scanning
calo ime y (TGA/DSC) s udy
The mal analysis was ca ied ou o cobal e i e p ecu so
gel o in es iga e he honey-media ed sol-gel au o-combus ion
p ocess o o ma ion o cobal e i e nanopa icles. Figu e1
shows TGA/DSC cu es o he d ied gel o e i e p ecu so s.
The TGA cu e exhibi s a mul i-s ep weigh loss. The weigh
loss om oom empe a u e o 110 °C is due o loss o esidual
wa e in he e i e p ecu so gel, which appea s on he DSC
cu e as an exo he mic peak a 90 °C [33]. The ea e , a
con inuous h ee-s ep weigh loss is no iced a empe a u e
anging om 148 °C o 350 °C. This also appea s as h ee
b oad exo he mic peaks a 154 °C, 252 °C, 350 °C on he
DSC cu e. The i s weigh loss is a ibu ed o he decom-
posi ion o he honey (i.e. uc ose and glucose). The second
exo he mic peak wi h la ge weigh loss is a ibu ed o he
decomposi ion o he d ied e i e p ecu so gels which was
ini ia ed by oxida ion– educ ion eac ion be ween he ni a e
and honey and e o lu ion o CO2 and NOx gases [34]. The
hi d exo he mic peak is a ibu ed o decomposi ion o he
o ganic esidual combus ion. The e is no u he weigh loss
a e 350 °C, he e o e, i indica ed pu e cubic cobal e i e
0 200 400 600 800 1000
0
20
40
60
80
100
Tempe a u e (
o
C)
Weigh (%)
0
10
20
30
40
50
60
Hea low (w/g)
Figu e 1. TGA/DSC s udy o sol-gel e i e p ecu so s o
o ma ion o cobal e i e nanopa icles by honey media ed sol-gel
au o-combus ion me hod.
Ad . Na . Sci.: Nanosci. Nano echnol. 8 (2017) 045002
R S Yada e al
4
spinel phase o ma ion a his empe a u e ia honey media ed
sol-gel au o-combus ion me hod.
3.2. S uc u al s udy
The phase o ma ion o syn hesized cobal e i e nanopa -
icles was in es iga ed by powde x- ay di ac ion. Figu e2
shows x- ay di ac ion (XRD) pa e ns o CoFe2O4 spinel
e i e nanopa icles syn hesized by honey media ed au o-
combus ion syn hesis and u he annealed a 500 °C, 700 °C,
900 °C, and 1100 °C.
The p esence o di ac ion planes (2 2 0), (3 1 1), (2 2 2),
(4 0 0), (4 2 2), (5 1 1), (4 4 0) in he di ac ion pa e ns con-
i ms ha all he samples exhibi cubic spinel s uc u e ha ing
space g oup Fd3m. All he di ac ion peaks a e well ma ched
wi h he s anda d JCPDS da a o CoFe2O4 (22-1086) [35].
The unindexed di ac ion peak in CoH7 sample is due
o p esence o α-Fe2O3 phase [36]. The b oad di ac ion
peak indica ed ha pa icles a e o nanosize ange. I is also
no iceable ha he di ac ion peaks a e sha pe and na owe
wi h an inc ease o annealing empe a u e. This indica ed
he imp o emen o c ys allini y wi h inc ease o annealing
empe a u e 500 °C, 700 °C, 900 °C and 1100 °C. The c ys-
alli e size and mic o-s ain analysis we e e alua ed using
Williamson–Hall me hod [37]. Acco ding o his me hod,
x- ay di ac ion peak b oadening
βhkl =βsize +βs ain
. The
ac ual peak b oadening (
β
) is ob ained by co ec ing he
expe imen al peak b oadening (
βex
) and he ins umen al
b oadening (
βin
) as
β2=β2
ex −β2
in
. Hence, XRD peak
b oadening
βhkl =βsize +βs ain
equa ioncan be in modi ied
o m as:
β
hkl =
0.94λ
Dcosθ
+4ε anθ
,
(1)
β
hklcosθ=
0.94λ
D
+4εsinθ
,
(2)
whe e β is ull wid h a hal maximum, λ is wa eleng h o
Cu-Kα adia ion (λ = 1.5406 Å), ε is s ain, and D is c ys al-
li e size. The Williamson Hall plo s o βcosθ e sus 4sinθ o
cobal e i e nanopa icles a e shown in igu e3. A linea plo
p o ides he in e cep as he c ys alli e size and he slope as he
s ain. The ob ained c ys alli e size and s ain o cobal e i e
nanopa icles a e abula ed in able1. I can be obse ed ha
Figu e 2. X- ay di ac ion pa e n o cobal e i e nanopa icles syn hesized by honey media ed sol-gel au o-combus ion syn hesis and
u he annealed a 500 °C, 700 °C, 900 °C, and 1100 °C.
Figu e 3. Williamson–Hall plo s o cobal e i e nanopa icles
syn hesized by honey media ed sol-gel combus ion me hod.
Ad . Na . Sci.: Nanosci. Nano echnol. 8 (2017) 045002

R S Yada e al
5
he c ys alli e size inc eases wi h inc ease o annealing empe -
a u e. The size o CoH sample is 20 nm and inc eases o 88 nm
o CoH11 sample. The s ain alue a ies om 1.7 × 10−3 o
CoH sample o −3.7 × 10−5 o CoH11 sample.
The la ice cons an o CoFe2O4 spinel e i e nanopa icles
has been calcula ed by d-spacing using he ela ion [38]
a=dhklh
2
+k
2
+l
2
(3)
whe e (h, k, l) a e he Mille indices. The la ice cons an was
ound o inc ease wi h inc ease o annealing empe a u e,
as shown in able 1. The inc ease in la ice cons an wi h
annealing obeys Vega d’s law [39]. The inc ease in la ice
cons an wi h inc ease o annealing empe a u e is associa ed
wi h a ia ion in mic os uc u e du ing annealing o ma e ial
and he mal ac i a ed o de ing o eo de ing o ca ions in
cubic spinel s uc u e.
X- ay densi y (dx) o CoFe2O4 spinel e i e nanopa icles
can be calcula ed by conside ing ha a basic uni cell o he
cubic spinel s uc u e con ains 8 ions [40] as ollows
dx=
8M
Naa
3
,
(4)
whe e M is he molecula weigh o sample, Na is A ogad o’s
numbe (6.0225 × 1023 pa icles/mole), and a is la ice pa am-
e e con e ed in o cm uni s. The x- ay densi y (dx) alues o
CoFe2O4 spinel e i e nanopa icles a e abula ed in able1.
I is ound ha he densi y is in luenced by he annealing
empe a u e. Densi y o cobal e i e nanopa icles wi h high
alues o he small sized pa icle was obse ed. Fu he , he
e ahed al (A)-si e adii ( A), oc ahed al (B)-si e adii ( B),
hopping leng h o e ahed al si e (dA), hopping leng h o
oc ahed al si e (dB), e ahed al and oc ahed al bond leng h
(dA× and dB×), e ahed al edge (dA×E), sha ed and unsha ed
oc a hed al edge (dB×E and dB×EU) o syn hesized cubic
CoFe2O4 spinel e i e nanopa icles a e e alua ed wi h la ice
cons an ‘a’, oxygen posi ional pa ame e ‘u’ (0.381 Å) and
oxygen ion adius Ro om he ollowing equa ions[41]:
A
=(
u−0.25
)
a√3−Ro, B
=(
0.625 −u
)
a−Ro,
dA=0.25a√3, dB=0.25a√2,
dA×=a√3(u−1/4),dB×=a[3u
2
−(11/4)u+(43/64)]1/2,
(5)
dA×E=a√2(2u−1/2),dB×E=a√2(1−2u),
dB×EU =a[4u
2
−3u+(11/16)]1/2.
The e alua ed alues o hese s uc u al pa ame e s a e ab-
ula ed in ables 1 and 2. I is no iceable ha he e alua ed
alue o dA and dB inc eases wi h inc ease o g ain size o
e i e nanopa icles. The inc ease in he alue o dA and dB
wi h inc ease g ain size is associa ed wi h inc ease in dis ance
be ween magne ic ions wi h inc ease o g ain size. I can be
also obse ed ha dA ˃ dB; which indica es ha he elec on
hopping be ween ions a e ahed al A si e and oc ahed al B
si e is less p obable han ha be ween oc ahed al B si e and
oc ahed al B si es. Fu he mo e, he e alua ed alue o A, B,
dA×, dB×, dA×E, dB×E, dB×EU inc eases wi h inc ease o g ain
size. I is also associa ed wi h ca ion edis ibu ion on g ain
size g ow h.
3.3. FESEM s udy
Figu e 4 shows he ield emission scanning elec on mic os-
copy (FESEM) mic og aphs o cobal e i e nanopa -
icles. I can be obse ed om FESEM image ha CoH
sample nanopa icles we e sphe ical wi h pa icle size ange
10–25 nm, as shown in igu e4(a). Fu he , i is also e iden
ha pa icle size inc eases wi h annealing empe a u e. The
CoH7 sample nanopa icles we e wi h g ain size 20–120 nm,
whe eas CoH11 sample nanopa icles we e in he ange o
70–150 nm, as ahown in igu es 4(b) and (c). Figu e 4(d)
shows he ypical EDX spec um o he ep esen a i e cobal
e i e sample. This spec um ma ks he p esence o Co, Fe
Table 1. C ys alli e size, s ain, la ice pa ame e , x- ay densi y (dx), adii o e ahed al and oc ahed al si es A and B, espec i ely, o
cobal e i e nanopa icles.
Sample
C ys alli e size
(nm) S ain
La ice
pa ame e (Å)
dx
(gm cm−3) A (Å) B (Å)
CoH 20 1.7 × 10−38.3817 5.292 0.5217 0.6651
CoH5 26 8.7 × 10−48.3844 5.287 0.5223 0.6657
CoH7 40 5.6 × 10−48.3862 5.284 0.5227 0.6662
CoH9 75 7.3 × 10−58.3875 5.282 0.5230 0.6666
CoH11 88 −3.7 × 10−58.3900 5.277 0.5236 0.6672
Table 2. Hopping leng h (dA) and (dB), e ahed al bond leng h (dA×), oc ahed al bond leng h (dB×), e ahed al edge (dA×E), sha ed (dB×E)
and unsha ed oc ahed al edge (dB×EU) o cobal e i e nanopa icles.
Sample dA (Å)dB (Å)dA× (Å)dB× (Å)dA×E (Å)dB×E (Å)dB×EU (Å)
CoH 3.6292 2.9629 1.9017 2.0462 3.1051 2.8207 2.9650
CoH5 3.6304 2.9639 1.9023 2.0469 3.1061 2.8216 2.9660
CoH7 3.6312 2.9645 1.9027 2.0473 3.1068 2.8222 2.9666
CoH9 3.6318 2.9650 1.9030 2.0477 3.1073 2.8226 2.9671
CoH11 3.6328 2.9658 1.9036 2.0483 3.1082 2.8235 2.9680
Ad . Na . Sci.: Nanosci. Nano echnol. 8 (2017) 045002
R S Yada e al
6
and O which u he con i ms he o ma ion o pu e CoFe2O4
spinel e i e.
3.4. Raman spec oscopy
Raman spec oscopy is a powe ul echnique o in es iga ing
he a omic s uc u e o nanopa icles [42]. Figu e 5 shows
he Raman spec a o CoFe2O4 spinel e i e nanopa icles.
G oup heo y analysis p edic s he ollowing op ical phonon
dis ibu ion: 5T1u + A1g + Eg + 3T2g, in which, he 5T1u
modes a e IR ac i e, whe eas he o he i e (A1g + Eg + 3T2g)
modes a e Raman ac i e composed o he mo ion o O
ions and bo h A-si e and B-si e ions in he spinel s uc u e
[43]. Fu he mo e, he A1g mode is associa ed o symme ic
s e ching o he oxygen anion, he Eg mode is associa ed o
symme ic bending o he oxygen anion, and he T2g mode is
due o asymme ic s e ching o he oxygen anion wi h espec
o he e ahed al and oc ahed al ca ions [44]. I can be seen
om igu e5 and able3 ha as syn hesized CoFe2O4 spinel
e i e nanopa icles shows Raman modes a ~198, ~297, ~461,
~558, ~604 and 680 cm−1. Raman modes a a ound 680 cm−1
shows a shoulde like ea u e a he lowe wa enumbe side
(~604 cm−1). These bands we e assigned o A1g(1) and A1g(2)
modes, demons a ing he s e ching ib a ions o he Fe–O
amd M–O bonds in e ahed al si es. The lowe equency
Raman modes (~198, ~297, ~461, and ~558 cm−1) we e
assigned o he T2g and Eg Raman modes, demons a ing he
ib a ion o he spinel s uc u e. I is also no iceable om
igu e 5 and able 3 ha he e we e a li le shi in Raman
modes wi h inc ease o annealing empe a u e. I was associ-
a ed wi h inc ease o pa icle size and ca ion edis ibu ion in
CoFe2O4 spinel e i e annealed samples [42–44]. The ca ion
edis ibu ion can be no iced by compa ing he ela i e in en-
si ies o he A1g(1) and A1g(2) modes. The change in a io o
in ensi y wi h inc ease o annealing empe a u e is obse ed
and i is abula ed in able3.
3.5. FTIR spec oscopy
The FTIR spec a o CoFe2O4 spinel e i e nanopa icles we e
eco ded in 75–900 cm−1 ange, a e as shown in igu e6. The
posi ions o he ib a ional bands o CoFe2O4 spinel e i e
a e abula ed in able4. In spinel e i e s uc u e, he ib a-
ional band a ound 550 cm−1 co esponds o he s e ching
ib a ion o e ahed al g oup and he ib a ional band a ound
350 cm−1 co esponds o he s e ching ib a ion o oc a-
hed al g oups [45]. F om igu e6 and able4, i can be seen
ha he FTIR spec a consis o wo majo abso p ion bands,
he i s a abou 550 cm−1 (ν1) and he second one a abou
Figu e 4. Cobal e i e nanopa icles wi h FESEM images (a) as p epa ed, (b) annealed a 700 °C, (c) annealed a 1100 °C, and EDX
pa e n (d).
Figu e 5. Raman spec a o cobal e i e nanopa icles a di e en
annealing empe a u es.
Ad . Na . Sci.: Nanosci. Nano echnol. 8 (2017) 045002
R S Yada e al
7
350 cm−1 (ν2). These abso p ion bands u he con i m he o -
ma ion o CoFe2O4 spinel e i e s uc u e. A small shi in he
abso p ion bands o he e ahed al and oc ahed al si es can
be obse ed om igu e6. The o ce cons an , which is p o-
po ional o a omic numbe o me al ions, a omic numbe o
oxygen ions and me al-oxygen bond leng h, is associa ed wi h
he shi o abso p ion band posi ion due o e ahed al (A)
si es and oc ahed al (B) si es, espec i ely [46]. Fu he , he
alue o o ce cons an , namely, FT and FB o he e ahed al
(A) and he oc ahed al (B) si es, espec i ely, a e e alua ed
om he ollowing equa ion[47]
F=4π2c2ν2µ,
(6)
whe e F is he o ce cons an , c is he ligh eloci y 2.99 × 108
m s−1, ν is he ib a ion equency o he A and B si es, µ
is he educed mass o he Fe3+ ions and he O2− ions
(~2.065 × 10−26 kg mol−1). The e alua ed alue o o ce con-
s an is abula ed in able4. The alue o o ce cons an o e -
ahed al si e was in he ange o 2.08 × 102 N m−1–1.97 × 102
N m−1, whe eas i was 0.82 × 102 N m−1 − 0.66 × 102 N m−1
o oc ahed al si e. The a ia ion o o ce cons an is associ-
a ed wi h ca ions edis ibu ion among e ahed al and oc a-
hed al si es wi h a ia ion o g ain size [48].
3.6. XPS s udy
XPS measu emen s we e ca ied ou o in es iga e elec-
onic s a e and ca ion dis ibu ion. I can be obse ed om
igu es 7(a) and (c), ha he high esolu ion Co 2p XPS
spec a o CoH5 and CoH11 sample is associa ed wi h wo
spin–o bi double s cha ac e is ics o Co 2p3/2 and Co 2p1/2
and wo shakeup sa elli es [49]. Figu e7(a) shows wo peaks
si ua ed a ~780 eV and ~795 eV, co esponding o he Co
2p3/2 and Co 2p1/2 o Co2+ s a e, which con i m ha he
alence s a e o cobal is 2. Fu he , o CoH5 sample, he Co
2p3/2 peak is decon olu ed in o wo peaks si ua ed a 780.2
and 782.6 eV ( igu e 7(a)), co esponding o Co in wo c ys al-
log aphic en i onmen , i.e. oc ahed al and e ahed al si es in
spinel e i e. The decon olu ed wo peaks ha e binding ene -
gies a 780.2 and 782.6 eV, which is associa ed wi h Co2+ ions
a oc ahed al si es and e ahed al si es, espec i ely. In acco -
dance wi h in eg a ed in ensi y o decon olu ed peaks, he
dis ibu ion o Co2+ ions is 70% a oc ahed al si es and 30%
a e ahed al si es. Simila ly, o CoH11 sample, he Co 2p3/2
spec a is also decon olu ed in o wo peaks si ua ed a 780.1
and 782.0 eV ( igu e 7(c)). The binding ene gies o decon o-
lu ed peaks a 780.1 and 782.0 eV a e assigned o Co2+ ions a
oc ahed al si es and e ahed al si es, espec i ely. In CoH11
sample, he dis ibu ion o Co2+ ions is 66% a oc ahed al
si es and 34% a e ahed al si es. Fu he , om igu es7(b)
and (d) i can also be obse ed ha he high esolu ion Fe
2p spec a o CoH5 and CoH11 sample, is associa ed wi h
wo spin–o bi double s cha ac e is ics o Fe 2p3/2 and Fe 2p1/2
and wo shakeup sa elli es [50]. Two peak si ua ed a ~711 eV
and ~725 eV ep esen he Fe 2p3/2 and Fe 2p1/2 o Fe3+ s a e,
con i ming ha he alence s a e o i on is 3. Fu he mo e,
wi h he in eg a ed in ensi y o decon olu ed peaks, he dis-
ibu ion o Fe3+ ions is 76% a oc ahed al si es and 24% a
e ahed al si es in CoH5 sample, whe eas, i is 77% a oc a-
hed al si es and 23% a e ahed al si es in CoH11 sample.
The e o e, he occupa ion o mula o CoFe2O4 nanopa icles
can be desc ibed as ollows
Co+2
0.30Fe+3
0.48Co+2
0.70Fe+3
1.52O
4
Table 3. Raman modes o cobal e i e nanopa icles.
Sample
Raman peak (cm−1)Ra io o in ensi y
IA1g(1)/IA1g(2)
A1g(1) A1g(2) T2g(1) T2g(2) EgT2g(3)
CoH 680 604 558 461 297 198 1.388
CoH5 680 603 561 463 287 221 1.433
CoH7 672 587 562 464 276 214 1.173
CoH9 678 599 559 460 287 217 1.447
CoH11 685 603 563 463 301 204 2.420
Figu e 6. FTIR spec a o cobal e i e nanopa icles a di e en
c ys alli e sizes.
Table 4. The equency ν1 and ν2 and o ce cons an FT and FB o
he e ahed al and oc ahed al si es, espec i ely, o cobal e i e
nanopa icles.
Sample ν1 (cm−1)ν2 (cm−1)
FT × 102
(N m−1)
FB × 102
(N m−1)
CoH 533 334 2.08 0.82
CoH5 529 333 2.05 0.81
CoH7 523 327 2.00 0.78
CoH9 521 314 1.99 0.72
CoH11 519 301 1.97 0.66
Ad . Na . Sci.: Nanosci. Nano echnol. 8 (2017) 045002
R S Yada e al
8
o CoH5 sample and
Co+2
0.34Fe+3
0.46Co+2
0.66Fe+3
1.54O
4
o CoH11 sample.
3.7. Magne ic p ope ies
Figu e 8 shows he a ia ion o magne iza ion as a unc ion o
applied magne ic ield o cobal e i e nanopa icles a oom
empe a u e. The hys e esis cu es show he a ia ion o mag-
ne iza ion wi h a ia ion o g ain size o e i e nanopa icles.
The e alua ed alue o a ia ion in magne ic pa ame e s such
as sa u a ion magne iza ion (Ms), emanence magne iza ion
(M ) and coe ci i y (Hc) a e abula ed in able5. Fu he , he
expe imen al magne ic momen (ηB) was e alua ed in acco -
dance wi h he ollowing ela ion [41]:
η
B=
MM
S
5585
,
(7)
whe e M is he molecula weigh . Mo eo e , he aniso opy
cons an is e alua ed using ollowing ela ion [51]
Hc=
0.96 K
MS
,
(8)
whe e K is aniso opy cons an .
In e omagne ic ma e ials, he magne iza ion will no
pass h ough o igin, howe e , a magne iza ion e sus applied
magne ic ield (M–H) loop, is o med. Figu e8 indica es e -
omagne ic beha iou o CoFe2O4 nanopa icles. Since, he
M–H loops do no pass h ough he o igin, he e o e, a ze o
applied magne ic ield, i e ains a magne iza ion alue, and i
is he emnen magne iza ion (M ). Coe ci i y is a measu e o
Figu e 7. XPS spec a o cobal e i e nanopa icles: (a, b) annealed a 500 °C, and (c,d) annealed a 1100 °C.
Figu e 8. Hys e esis cu e o cobal e i e nanopa icles a
di e en c ys alli e sizes.
Ad . Na . Sci.: Nanosci. Nano echnol. 8 (2017) 045002