In luence o isoch onal annealing on he mic os uc u e and magne ic p ope ies o Cu-
ee HITPERM Fe40.5Co40.5Nb7B12 alloy
P. Gup a, Tapas Ganguli, A. Gup a, A. K. Sinha, S. K. Deb, P. S ec J ., and V. F anco
Ci a ion: Jou nal o Applied Physics 111, 113518 (2012); doi: 10.1063/1.4728161
View online: h p://dx.doi.o g/10.1063/1.4728161
View Table o Con en s: h p://sci a ion.aip.o g/con en /aip/jou nal/jap/111/11? e =pd co
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In luence o isoch onal annealing on he mic os uc u e and magne ic
p ope ies o Cu- ee HITPERM Fe
40.5
Co
40.5
Nb
7
B
12
alloy
P. Gup a,
1
Tapas Ganguli,
1
A. Gup a,
2
A. K. Sinha,
1
S. K. Deb,
1
P. S ec J .,
3
and V. F anco
4
1
Indus Synch o on U iliza ion Di ision, Raja Ramanna Cen e o Ad anced Technology, Indo e 452013,
India
2
UGC-DAE Conso ium o Scien i ic Resea ch, Uni e si y Campus, Khandwa Road, Indo e 452017, India
3
Ins i u e o Physics, Slo ak Academy o Sciences, Dub a ska ces a 9, 845 11 B a isla a, Slo akia
4
Dp o. Fı´sica de la Ma e ia Condensada, ICMSE-CSIC, Uni e sidad de Se illa, P.O. Box 1065, Se illa 41080,
Spain
(Recei ed 28 Janua y 2012; accep ed 8 May 2012; published online 7 June 2012)
Sys ema ic s udy o he e ec o isoch onal annealing on he s uc u e and magne ic p ope ies o
Cu- ee HITPERM alloy (Fe
40.5
Co
40.5
Nb
7
B
12
) is desc ibed he ein. Mo¨ssbaue spec oscopy (MS)
and anomalous x- ay di ac ion (XRD) measu emen a Fe K-edge (7.112 keV) join ly p o ide
clea e idence o he p esence o a omically o de ed a0-FeCo (B2 s uc u e) phase as a
nanoc ys alline e omagne ic phase. Being a sho ange o de p obe, Mo¨ssbaue spec oscopy also
con i ms he de elopmen o an addi ional non-magne ic Nb- ich phase in he nanoc ys alline
specimens (annealed abo e 723 K) wi h simul aneous lowe ing o he olume ac ion o
e omagne ic phases. The ac ion o Fe a oms in he non-magne ic phase is 15% upon annealing
a 773 K o 1 h, which inc eases g adually and eaches o as high as 19% a e annealing a 923 K.
This phase was no de ec ed by XRD and ansmission elec on mic oscopy (TEM) measu emen s,
which may be a ibu ed o iny c ys alli e size and/o high deg ee o diso de . In he second s age o
c ys alliza ion, i.e., abo e 923 K, he alloy becomes ully c ys alline and a s able, ha d magne ic
cc-(FeCo)
23
B
6
ype phase was obse ed as a main bo ide phase along wi h so magne ic a0-FeCo
phase and Nb ich non-magne ic phase. The mo magne ic measu emen e idenced e-c ys alliza ion
p ocess as a conside able dec ease in magne iza ion a he second ans o ma ion s age.
Simul aneous lowe ing o he olume ac ion o magne ic phases wi h he o ma ion o
non-magne ic phase p o ides con incing o igin o he dec ease in magne iza ion a he second
c ys alliza ion s age. V
C2012 Ame ican Ins i u e o Physics.[h p://dx.doi.o g/10.1063/1.4728161]
I. INTRODUCTION
Nanoc ys alline alloys, which consis o nanosized e -
omagne ic c ys als embedded in a esidual e omagne ic
amo phous ma ix, exhibi excellen so magne ic p ope ies
such as low coe ci i y, high sa u a ion magne iza ion, high
pe meabili y, and low hys e esis losses. Technical applica-
ions equi e ma e ials wi h s able and good so magne ic
p ope ies o e a wide empe a u e and ime ange. Fe based
nanoc ys alline alloys p oduced by con olled pa ial c ys al-
liza ion o amo phous p ecu so s (ob ained by apid quench-
ing o m he mel ) a e he bes known so magne ic
ma e ials ill da e. They can be classi ied as: FINEMET
(FeSiCuNbB),
1
NANOPERM (FeCu (Z , Nb, H ) B),
2
and
HITPERM FeCo (Z , Nb, H ) B (Cu)
3
alloys. The c ys alli-
za ion o such alloys occu s in wo ans o ma ion s ages, in
he p ima y s age o c ys alliza ion a-Fe
3
Si nanoc ys alline
g ains wi h a DO
3
c ys al s uc u e ( o Fineme alloys),
a-Fe nanoc ys als wi h body-cen e ed-cubic (bcc) (A2) s uc-
u e ( o Nanope m), nanoc ys alline a0-FeCo g ains wi h
B2 s uc u e ( o HITPERM) a e o med. De i i ica ion
p ocess is comple ed in he second ans o ma ion s age,
occu ing a highe empe a u e whe e ab up dec ease in
so magne ic p ope ies is obse ed wi h he o ma ion o
di e en ha d magne ic and/o non-magne ic bo ide and
nioba e phases.
In he nanoc ys alline s a e, whe e he nanosized e o-
magne ic c ys alline g ains a e embedded in a esidual e o-
magne ic amo phous ma ix, he so magne ic p ope ies
a ise om he exchange in e ac ion be ween he andomly
o ien ed nanoc ys alline g ains (5–20 nm) h ough he in e -
ening amo phous ma ix (a omic scale),
1
whe e he smoo h-
ing ac ion o exchange ene gy dec eases he e ec i e
aniso opy.
4
The exchange coupling among hese g ains
de e io a es abo e he Cu ie empe a u e o amo phous ma-
ix, which in u n de e io a es he so magne ic p ope ies
in such sys ems. The e o e, FINEMET and NANOPERM
alloys ha e low he mal limi a ion.
High empe a u e powe applica ions equi e ha he
so magne ic p ope ies o hese alloys should be main ained
up o ele a ed empe a u es.
5
Due o p esence o Co, HIT-
PERM ype alloys possesses high Cu ie empe a u e o
amo phous and nanoc ys alline phases and main ains high
induc ion (1.6–2.1 T) up o ele a ed empe a u es as com-
pa ed o FINEMET and NANOPERM and hus a e sui able
ma e ials o ope a ion a high empe a u es.
6
Cu ee HITPERM alloys possess lowe alues o coe -
ci i y as compa ed o Cu con aining HITPERM alloys.
7
In
addi ion o his, because Cu a oms do no o m clus e s, he
g ain sizes in he nanoc ys alline s a e o Cu-con aining and
Cu- ee alloys a e ound o be almos same.
8
The e o e,
Cu- ee alloys ha e he bene i o inc easing he sa u a ion
0021-8979/2012/111(11)/113518/10/$30.00 V
C2012 Ame ican Ins i u e o Physics111, 113518-1
JOURNAL OF APPLIED PHYSICS 111, 113518 (2012)
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magne ic lux densi y.
9
Howe e , i may be no ed ha he
la e ansi ion me als (Z , Nb, Mo e c.) a ec s he d i ing
o ce o he Cu clus e ing phenomenon o such alloys.
10
The so magne ic p ope ies o such nanoc ys alline
alloys ha e s ong co ela ion wi h how he nanoc ys alline
phases e ol e upon hea ea men unde sui able condi-
ions.
11
The e o e, he op imiza ion o mic os uc u e and
magne ic p ope ies unde he in luence o some p ocessing
echnique (such as he mal p ocessing) is impo an o
applica ion o hese alloys as so magne ic ma e ials. Con-
olled annealing ea men can pa e a way in con olling he
magne ic p ope ies o he amo phous as well as nanoc ys al-
line phases and hence he so magne ic p ope ies o he
alloy composi ion. The de ailed in es iga ion on he e ec o
annealing is expec ed o p o ide a be e unde s anding o
he mic os uc u e and magne ic p ope ies.
In addi ion o his, Willa d e al.
12
p o ided unambigu-
ous e idence abou he a omically o de ed a0-FeCo phase as
he nanoc ys alline phase in FeCoZ BCu alloys. Howe e ,
he e is no expe imen al e idence, whe he he Cu ee Hi -
pe m alloy has ei he an a omically o de ed o a diso de ed
FeCo nanoc ys alline phase. I is impo an o no e ha due
o simila a omic sca e ing ac o s o Fe and Co, he e is am-
bigui y in dis inguishing be ween he diso de ed a-FeCo
phase and o de ed a0-FeCo phase by he con en ional XRD
measu emen , in he nanoc ys alline s a e o such alloys.
Close o he abso p ion edges o he cons i uen s (Fe o Co),
he anomalous sca e ing ac o s play an impo an ole and
he di e ence in he a omic sca e ing ac o s enhances sig-
ni ican ly, which makes he obse a ion o supe la ice
e lec ion possible, in case o he o de ed phase.
13
In he p esen wo k, mel spun Fe
40.5
Co
40.5
Nb
7
B
12
alloy
was isoch onally annealed a di e en empe a u es o e a
wide ange o empe a u es and he ela ion be ween he
mic os uc u e and magne ic p ope ies o he alloy was
in es iga ed using complemen a y echniques o synch o on
adia ion based x- ay di ac ion (SR-XRD), TEM, Mo¨ssba-
ue spec oscopy, di e en ial scanning calo ime y (DSC),
and he mo-magne ic g a ime e y (TMG). The deg ee o
a omic o de ing o he nanoc ys alline FeCo phase was also
de e mined by anomalous x- ay sca e ing measu emen a
Fe K-edge (7.112 keV).
II. EXPERIMENTAL
Alloy o nominal composi ion Fe
40.5
Co
40.5
Nb
7
B
12
was
p epa ed by a c mel ing high pu i y elec oly ic Fe, Co, Nb,
and B me als basis in an a gon a mosphe e. Amo phous ib-
bons, 6 mm wide and abou 20 lm hick, we e p oduced
om he ingo s using a single wheel mel spinning ech-
nique. Chemical composi ion o he ibbon was checked by
induc i ely coupled plasma spec oscopy and no de ec able
de ia ion om he nominal composi ion was obse ed. The
ibbons we e isoch onally annealed o 1 h in a ubula u -
nace unde acuum a mosphe e (be e han 10
5
To ) a
empe a u es anging om 573 K o 973 K. A di e en ial
scanning calo ime e was used o examine he c ys alliza ion
empe a u es o an as-cas ibbon. A scanning a e o
10 K/min was used o empe a u es be ween 300 K and
873 K. The s uc u es o he as-spun and annealed ibbons
we e examined by SR-XRD and TEM. X- ay di ac ion
measu emen s we e pe o med a ADXRD beamline o
Indus-2 synch o on sou ce, India,
14
u ilizing he monoch o-
ma ic x- ays o ene gy 15 keV. Image pla e a ea de ec o was
used o eco d he spec a. La hanum hexabo a e (LaB
6
) was
used as s anda d ma e ial o calib a ion. In o de o dis in-
guish o de ed a0-FeCo phase om he diso de ed a-FeCo
phase, anomalous XRD measu emen s we e also pe o med
by choosing he x- ay ene gy o 7.112 keV (Fe-Kedge). All
samples o TEM we e isoch onally annealed in high ac-
uum (be e han 7.5 10
7
To ) a di e en empe a u es
and subsequen ly polished by ion beam milling using Ga an
PIPS. TEM obse a ions we e pe o med using JEOL 2000
FX. Fo all he annealed specimens, he
57
Fe Mo¨ssbaue
measu emen s a oom empe a u e in ansmission geome y
ha e been done using a
57
Co: Rh sou ce and a cons an
accele a ion Mo¨ssbaue d i e. To cha ac e ize he mal
beha io o he magne iza ion o he alloy, he momagne ic
g a ime e y was pe o med using Pe kin-Elme TGA-7.
A e elec onically cancelling he sample weigh , an appa-
en weigh was eco ded a e placing a magne (magne ic
ield 20 mT) below he sample pan. Hea ing was hen ca -
ied ou om 323 K o 1123 K wi h a a e o 10 K/min.
Changes in he magne ic o ce ac ing on he sample a e
ela ed o he a ia ions in magne iza ion wi h empe a u e
and a e eco ded as appa en weigh change o he sample.
III. RESULTS AND DISCUSSION
A. DSC measu emen
Figu e 1shows he DSC he mog am o he as-quenched
samples measu ed in he empe a u e ange whe e he p ima y
c ys alliza ion akes place. The exo he mal peaks wi h onse a
T
onse
and he peak posi ion a T
c ys1
co espond o he o ma-
ion o he nanoc ys alline bcc-FeCo. Fo Fe
40.5
Co
40.5
Nb
7
B
12
alloy, T
onse
742 K and T
c ys1
768 K has been de ec ed. I
may be no ed ha T
onse
is ob ained as he in e sec ion o he
la ges slope o he exo he mal peak wi h he baseline o he
DSC eco d and T
c ys
is he empe a u e o he peak. In gene al,
600 650 700 750 800 850
-2
-1
0
1
2
3
4
Fe40.5Co40.5Nb7B12 alloy
Hea Flow (mW)
T(K)
Tc ys1
Tonse
FIG. 1. DSC scan o as-cas Fe
40.5
Co
40.5
Nb
7
B
12
alloy.
113518-2 Gup a e al. J. Appl. Phys. 111, 113518 (2012)
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he Nb-con aining HITPERM ype alloys ollow a wo s ep
c ys alliza ion p ocess.
15,16
The p ima y c ys alliza ion s age
(abo e 700 K) p oduces bcc-FeCo nanoc ys als dispe sed in e-
sidual amo phous ma ix. The alloy becomes ully c ys alline
in a seconda y c ys alliza ion s age (abo e 900 K) wi h he p e-
cipi a ion o addi ional bo ide and nioba e phases.
17
B. XRD measu emen
Figu e 2gi es SR-XRD spec a o he alloy in he
annealed s a e wi h some ep esen a i e aw image pla e pa -
e ns, illus a ing he mic o s uc u al e olu ion o he sam-
ples as a unc ion o annealing empe a u e. Fo compa ison,
he spec um o he alloy in he as-quenched s a e is also
included in he same igu e. The sample- o-image-pla e dis-
ance was 125.36 mm. The image pla e da a iles we e in e-
g a ed using FIT2D, inco po a ing pola iza ion co ec ion.
18
In he as p epa ed s a e, XRD pa e n shows a b oad
halo, which is cha ac e is ic o he amo phous phase. Wi h
p og essi e s ages o annealing, he sys em g adually ans-
o ms o nanoc ys alline phase. The XRD spec a o he as-
quenched alloy can be i ed by a Lo en zian unc ion wi h
ull wid h a hal maximum o 3.2260.02. The XRD pa -
e ns o he annealed specimens show ha a e annealing a
723 K ( empe a u e co esponds o onse o c ys alliza ion),
he b oad halo s a ed shaping in o na ow peak and he alloy
becomes pa ially nanoc ys alline, whe e nano-c ys als a e
dispe sed in he emaining amo phous ma ix (Fig. 2). This
nanoc ys alline phase comp ises o bcc-Fe (Co) phase as
indica ed by sha p peaks in he XRD pa e n o he specimen
annealed a 773 K, a 2h alues o 23.51, 33.52, 41.36,
and 48.14wi h some small indica ion o amo phous phase.
The ela i e in ensi ies ma ch well wi h he JCPDS da a-
base
19
and addi ionally he di ac ion ings a e o uni o m
in ensi y (Fig. 2(b)), which shows ha he c ys alli es ha e
andom o ien a ion.
20
In case o annealed specimens, he assump ion o single
Lo en zian o he i ing was ound o be alid only up o
658 K, whe e he specimen emained in he pu e amo phous
s a e. F om 723 K onwa ds, da a we e i ed by aking he
supe posi ion o Lo en zian and Gaussian peaks: Lo en zian
co esponds o he amo phous phase and Gaussian o he
nanoc ys alline phase. I may be no ed ha wi h inc easing
annealing empe a u e (up o he empe a u e o 923 K), di -
ac ion peaks co esponding o bcc-FeCo nanoc ys alline
phase become p og essi ely sha pe bu he peak posi ion
emains nea ly una ec ed o he whole ange o annealing
empe a u e. A e annealing a 973 K (well abo e he end o
p ima y c ys alliza ion), he peak co esponding o (110)
e lec ion o Fe, Co nanoc ys alline phase becomes e y
sha p and he alloy becomes ully c ys alline. No signa u e
o he emaining amo phous phase was obse ed. Close
inspec ion o he spec a in he ully c ys alline s a e o he
alloy sugges s ha a ious addi ional small peaks s a
appea ing which co espond o di e en bo ide- ype phases
such as (FeCo)
3
B, (FeCo)
2
B and (FeCo)
23
B
6
phases and
(FeCo)
3
Nb nioba e phase.
15,17,21
S udies on he c ys alliza-
ion o FINEMET alloys ha e exhibi ed such ha d magne ic
bo ide phases upon joule hea ing.
22
The a e age c ys alli e size (D) and la ice mic o-s ain
(e) o FeCo phase was es ima ed by applying he
Williamson-Hall me hod.
23
The physical line b oadening B
is a sum o line b oadening connec ed o c ys alli e size (D)
and o line b oadening connec ed o la ice s ain (e). Fo he
Gaussian x- ay p o iles, Williamson-Hall equa ion is
exp esses as,
24
ðBcos hÞ2¼kk
D

2
þðesin hÞ2;(1)
whe e B is he ull wid h a hal maximum o XRD peaks, k
is Sche e cons an , kis he wa eleng h o x- ay, and his
he B agg angle. The line b oadening and he posi ion o he
ou B agg peaks we e used o es ima e he mean c ys alli e
size, (D) and la ice mic o-s ain (e). Figu e 3shows he cal-
cula ed Dand e alues o he alloy as a unc ion o inc eas-
ing annealing empe a u e. The esul s indica e ha he
c ys alli e size inc eases wi h inc easing annealing empe a-
u e. Upon annealing a 973 K, when he sys em is com-
ple ely c ys allized, he size o c ys alli e u he inc eases
and a ains a alue o 13 nm (Fig. 3(a)). I may be no ed
ha he e inemen o g ain size below e omagne ic
exchange leng h, L
0
(46 nm o equia omic FeCo alloy
7
), is
necessa y o ob ain supe io so magne ic p ope ies in such
alloys.
25
Fu he mo e, he dec ease in la ice mic o-s ain
wi h empe a u e (Fig. 3(b)) indica es imp o ed c ys alline
quali y wi h inc easing c ys alli e size o FeCo nanoc ys al-
line phase.
The la ice pa ame e o he nanoc ys alline phase, as
calcula ed om he esul s o XRD measu emen s, ini ially
exhibi a small dec ease (0.3%) wi h annealing empe a u e
and hen becomes almos cons an o annealing empe a-
u es g ea e han 823 K (Fig. 4). The dec ease in la ice
10 15 20 25 30 35 40 45 50 55
0402
923 K
(220)
(211)
(200)
o
'
-(Fe,Co) Phase
573 K
973 K
873 K
823 K
773 K
723 K
658 K
In ensi y ( a b. uni s )
(deg ees)
Fe
44.5
Co
44.5
Nb
7
B
12
alloy
As-quenched
(110)
973 K
(ii)
FIG. 2. (a): XRD pa e ns o he Fe
40.5
Co
40.5
Nb
7
B
12
alloy a e annealing
up o he onse o second c ys alliza ion s age. Fo compa ison XRD pa e n
o he as p epa ed sample is also shown. The beam ene gy used o hese
measu emen s was 15 keV. (b) Inse shows aw image pla e x- ay di ac ion
da a o (i) as p epa ed sample, (ii) annealed a 873 K, and (iii) annealed a
973 K.
113518-3 Gup a e al. J. Appl. Phys. 111, 113518 (2012)
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pa ame e is co ela ed wi h he inc ease in c ys alli e size.
Gene ally o such alloy sys ems, he densi y o c ys alline
phase is highe han ha o he amo phous phase; he e o e
as he dense c ys alline phase p ecipi a es ou , i will expe i-
ence a ensile s ess due o su ounding amo phous ma ix.
The e o e, he associa ed s ain in c ys alline FeCo phase
will dec ease wi h inc easing c ys alli e size. This ini ial
dec ease in la ice pa ame e may hus be unde s ood in
e ms o dec ease in he e ec o ensile s ess exe ed by he
low densi y amo phous ma ix on he nanoc ys alline phase
wi h inc ease in c ys alli e size.
26
The a io o he a ea o he nanoc ys alline phase o ha
o he sum o he a eas o he nanoc ys alline and he amo -
phous phases was used o calcula e he c ys alline ac ion o
he nanoc ys alline phase.
27
As expec ed, wi h inc easing
c ys alliza ion, he c ys alline ac ion was ound o be
inc easing, and inally a 973 K, c ys alliza ion o nanoc ys-
alline FeCo phase comple es ( ull c ys alliza ion), and a
his empe a u e, a e y good i ing o he da a was ob ained
by Gaussian p o ile co esponding o he single c ys alline
phase.
F om he con en ional XRD pa e n, i is di icul o
de ec he co ec s uc u e (o de ed o diso de ed) in case o
alloys o compounds o he ype FeCo, CuZn e c, which
di e in a omic numbe by only one o wo uni s. I is
because he supe la ice (SL) line in ensi y is in gene al p o-
po ional o (
A

B
)
2
, whe e
A
and
B
a e a omic sca e ing
ac o s o elemen s A and B, espec i ely. The a omic sca -
e ing ac o s o elemen A and elemen B a e e y simila
o exci a ion by a s anda d labo a o y sou ce (Cu K
a
), and
he SL in ensi y is, he e o e, e y weak as compa ed o un-
damen al line (FL) in ensi y.
13
Howe e , he co ec s uc-
u e can be ob ained when he inciden wa eleng h kis
nea ly equal o wa eleng h k
K
o he K-abso p ion edge o
he one o he sca e ing elemen (ei he A o B). Close o he
abso p ion edges o he cons i uen s (Fe o Co in case o
FeCo alloy), he a omic sca e ing ac o s o he sca e ing
elemen s ge signi ican ly modi ied due o he con ibu ion o
anomalous dispe sion e ec s. This inc eases he di e ences
in he a omic sca e ing ac o s be ween he elemen s,
he eby enhancing he in ensi y o he supe la ice e lec ion
ela i e o ha o he undamen al line and hence makes he
obse a ion o supe la ice e lec ion possible, in case o an
o de ed s uc u e.
In he comple e o de ed s a e o FeCo alloy, each uni
cell will con ain one Fe a om, a (0, 0, 0) and one Co a om a
(1
=2,1
=2,1
=2). The e o e, he s uc u e ac o ,
F¼ Fe þ Co½epiðhþkþlÞ;
F¼ Fe þ Co o ðhþkþlÞe en;
F¼ Fe  Co o ðhþkþlÞodd:(2)
The o de ed s uc u e hus p oduces di ac ion lines o all
alues o hkl, and he e o e, i esembles he di ac ion pa -
e n o a simple cubic subs ance. Fo a ully o de ed alloy,
in ensi y o SL line (100) ela i e o ha o he undamen al
line (110) can be es ima ed as
in ensi yðSLÞ=in ensi y ðFLÞ¼p1
sin2hcos h

ð Fe  CoÞ2
ð Fe þ CoÞ2
!
(3)
whe e p is he mul iplici y ac o and he igonome ic e ms
co espond o he Lo en z ac o . When kis nea k
k
, he
a omic sca e ing ac o would be
F¼ 0þD ;(4)
whe e 0is he a omic sca e ing ac o when kkkand D
is change in 0when kis nea kk. He e, k/k
k
is 1.00 o he
Fe a om and 1.08 o Cobal a om, and he alue o D is
hen abou 5.0 o Fe a om and 2.7 o Cobal a om;
13
he e o e a a 2h alue o 35.71
o
(whe e he SL peak is
obse ed expe imen ally), he in ensi y o he SL e lec ion
would be p opo ional o 10.4 including he mul iplici y
ac o and Lo en z ac o . The a io o he SL e lec ion ela-
i e o FL e lec ion is e alua ed o be 0.012. Howe e , his
a io co esponds o 0.00035 when kkk. In he p esen
case, anomalous XRD measu emen s was pe o med a Fe
K-edge (7.112 keV) o he specimen annealed a 823 K o
750 800 850 900 950 1000
-6.0x10-4
0.0
6.0x10-4
1.2x10-3
1.8x10-3
2.4x10-3
3.0x10-3
8
10
12
14
(b)
La ice s ain
Tempe a u e (K)
La ice s ain
D (nm)
C ys alli e size
(a)
FIG. 3. Va ia ion o c ys alli e size (D) and la ice mic o-s ain (e)o he
FeCo nanoc ys alline phase as a unc ion o inc easing annealing empe a u e.
750 800 850 900 950 1000
2.846
2.848
2.850
2.852
2.854
2.856
2.858
2.860
2.862
2.864
2.866
Tempe a u e (K)
FIG. 4. Va ia ion in la ice cons an wi h inc easing annealing empe a u e.
113518-4 Gup a e al. J. Appl. Phys. 111, 113518 (2012)
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de ec ion o co ec s uc u e (o de ed o diso de ed) o
Fe
40.5
Co
40.5
Nb
7
B
12
alloy and is shown in Fig. 5. P esence o
weak (100) supe -la ice e lec ion along wi h he (110) un-
damen al e lec ion indica e he p esence o a omically o -
de ed FeCo nanoc ys alline phase ha ing B2 s uc u e. The
di ac ion pa e n was i ed by a supe posi ion o h ee Lo -
en zian peaks: one co esponds o (100) SL e lec ion and
he o he wo co espond o amo phous and nanoc ys alline
phases o (110) e lec ions. The in eg a ed in ensi y a io o
(100) SL e lec ion ela i e o ha o (110) e lec ion is es i-
ma ed as 0.0117. This is in good ag eemen (wi hin 2.5%)
wi h he calcula ed in ensi y a io. I may be no ed ha he
o de ing o a-FeCo nanoc ys alline phase in such alloys
depends on Fe, Co composi ion
28,29
as well as on he p epa-
a ion condi ions.
30
Fu he , XRD measu emen s also p o ide de ailed in o -
ma ion abou he s uc u al changes occu ing in he emain-
ing amo phous g ain-bounda y phase. In he amo phous
phase, he a oms do no ha e a long ange o de and only
sho ange o de exis s. The sho ange o de can be
exp essed by a adial dis ibu ion unc ion 4p 2qð Þsuch
ha 4p 2qð Þd is he a e age numbe o a oms cen e s
be ween and þd om he cen e o an a e age a om.
31
The adial dis ibu ion unc ion is gi en by
4p 2qð Þ¼4p 2qoð Þþ2
pð1
0
kiðkÞsinð kÞdk (5)
whe e qoð Þis he a e age densi y in a oms/A
˚
3
,k¼4psinðhÞ
k
is ecip ocal la ice ec o (A
˚
1
), and iðkÞis he modi ied
sca e ing in ensi y. I may be no ed ha he exp ession
abo e is alid o he amo phous sample con aining only one
kind o a om. In he FeCoNbB alloy unde s udy, Fe and Co
ha e e y close a omic numbe s and hey o m abou 81% o
composi ion, B o ms 12% o composi ion bu i is a poo
x- ay sca e e and Nb o ms only 7% o he composi ion,
whose con ibu ion in sca e ing is small and hus igno ed.
Conside ing only one kind o a om, he adial dis ibu ion
unc ion has been calcula ed o he as-quenched as well as
annealed Fe
40.5
Co
40.5
Nb
7
B
12
alloy be o e he onse o c ys-
alliza ion. Fo all he samples in he pu e amo phous s a e,
TM-TM dis ance is ound o be nea ly iden ical and equals
o 2.69 A
˚, whe e TM deno es ansi ion me al. Figu e 6
shows he ep esen a i e adial dis ibu ion unc ion (RDF)
o he sample annealed a 658 K, whe e he alloy emains in
he pu e amo phous phase. In gene al, he posi ion o he i s
b oad maximum can be used o calcula e he dis ance
be ween he nea es neighbo a oms (X
m
) in he amo phous
phase using he ela ion, Ck¼2Xmsinh, whe e Cis a con-
s an and gene ally aken as 1.23.
32
Upon compa ison o he
ansi ion me al- ansi ion me al (TM-TM) dis ance as
ob ained om he RDF, he alue o Cwas ound o be
1.31 o he p esen se o expe imen s. This has been used
o es ima e he TM-TM dis ance, om he amo phous con i-
bu ion, in he pa ially c ys alline samples. Figu e 7gi es he
a ia ion in he a e age TM–TM nea es neighbou dis ance
in he amo phous phase, as ob ained om he posi ion o he
b oad amo phous peak. Be o e nanoc ys allisa ion, he TM-
TM dis ance dec eases sligh ly, his could be unde s ood in
e ms o s uc u al elaxa ion, which is expec ed o esul in
annihila ion o de ec s and excess ee olume and hus
should esul in a dec ease in he TM-TM nea es neighbo
dis ance. A mono onous inc ease in he TM–TM dis ance
upon nanoc ys allisa ion may be a ibu ed o en ichmen o
he amo phous phase in me alloid.
33
I may be no ed ha he
x- ay sca e ing om he me alloid a oms is signi ican ly
30 40 50 60
E= 7.112 keV (Fe K-edge)
Å
In ensi y ( a b. uni s )
deg.
(110)
(100)
'
-FeCo Phase
FIG. 5. SR-XRD measu emen a 7.112 keV con i ms he o de ed a0-Fe, Co
phase by he p esence o (100) supe la ice e lec ion.
FIG. 6. Radial dis ibu ion unc ion o he Fe
40.5
Co
40.5
Nb
7
B
12
alloy in i s
pu e amo phous s a e.
300 400 500 600 700 800 900 1000
0.60
0.65
0.70
0.75
0.80
0.85
0.90
2.67
2.68
2.69
2.70
2.71
2.72
Tempe a u e (K)
wid h o amo phous halo
Xm
FIG. 7. A e age TM–TM nea es neighbou dis ance and wid h o he amo -
phous halo as a unc ion o annealing empe a u e.
113518-5 Gup a e al. J. Appl. Phys. 111, 113518 (2012)
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weak as compa ed o ha om he TM a oms. The wid h o
he amo phous halo o he XRD pa e n, which is a measu e
o he deg ee o diso de in he amo phous phase, exhibi s an
in e es ing beha io wi h annealing empe a u e, as shown in
Figu e 7. This beha iou may be unde s ood as ollows. Ini-
ially, annealing in he empe a u e ange 573–823 K causes
a dec ease in he diso de . This may be connec ed o s uc-
u al elaxa ion in he amo phous phase, which esul s in an
inc eased opological o de in he sys em. Annealing a
highe empe a u es esul s in a sha p inc ease in he diso de
and hen shows a apid dec ease. Ini ially, wi h inc easing
c ys alliza ion, as me alloid is expelled ou o nanoc ys al-
line g ains, i will o m a concen a ion g adien a ound he
c ys alli es. Howe e , o highe annealing empe a u e me -
alloid dis ibu es a he uni o mly h oughou he amo phous
phase, esul ing in a ela i ely homogeneous dis ibu ion.
33
This edis ibu ion a ec s he magne ic p ope ies o he
amo phous phase and he so magne ic p ope ies o he
nanoc ys alline alloy.
C. T ansmission elec on mic oscopy
The mic os uc u e and selec ed a ea elec on di ac ion
pa e ns o he sample in di e en s ages o ans o ma ion
a e shown in Figs. 8(a) and 8(b). The obse ed g ain sizes o
he bcc-phase (Fig. 8(a)-inse s (i)–(iii)) a e in acco dance
wi h he alues de e mined om XRD analysis. TEM images
show ha he e is no signi ican size e olu ion o he bcc-
phase pa icles wi h annealing empe a u e. Howe e , he
pa icles seem o be dis ibu ed in a no comple ely andom
manne (see images in Fig. 8(a)-inse s (i) and (ii)); his e ec
is enhanced in he s ages p io o he o ma ion o he
(FeCo)
23
B
6
ype phase and possibly e lec s he medium-
ange o de , which may be a p ecu so o he o ma ion o
complex (FeCo)
23
B
6
phase. The pa icles o his phase, espe-
cially in he inal s age o i s o ma ion, seem o consis o
se e al g ains and ange up o 300 nm in size. No p e e en ial
o ien a ion o he cc-phase wi h espec o he ibbon su ace
has been obse ed. I is o be no ed ha he pa icles o bcc-
FIG. 8. (a) E olu ion o mo phology
du ing ans o ma ion om amo phous
s a e (b igh ield images): inal s ages o
nanoc ys allisa ion, sample annealed a
873 K/1 h (i) and 923 K/1 h (ii) ini ial
s ages o o ma ion o (FeCo)
23
B
6
phase,
sample annealed a 948 K/1 h (iii) com-
ple ely c ys allized sample annealed a
973 K/1 h (i ) wi h ully de eloped
g ains o (FeCo)
23
B
6
. (b) Le -di ac ion
pa e n om he sample annealed a
923 K/1 h showing he p esence o bcc-Fe
(Co) phase (indices in he cen al pa o
he image) wi h aces o amo phous
emains. Righ -di ac ion pa e n om
he cen al pa icle in (a) (iii) (973K/1 h,
b igh ield) showing he p esence o cc-
phase o he (FeCo)
23
B
6
ype (zone axis
111) oge he wi h ings o bcc-Fe (Co).
113518-6 Gup a e al. J. Appl. Phys. 111, 113518 (2012)
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Fe (Co) e ain hei small size e en a e ull c ys alliza ion
o he sample.
D. Mo¨ssbaue measu emen s
Mo¨ssbaue spec oscopy has been used as a complemen-
a y ool o he de e mina ion o he s uc u e and magne ic
p ope ies o he Fe
40.5
Co
40.5
Nb
7
B
12
alloy as a unc ion o
isoch onal annealing. Figu e 9 ep esen s Mo¨ssbaue spec a
o he alloy along wi h he i ings in he as-quenched s a e as
well as a e isoch onal annealing a a ious empe a u es up
o 973 K. In he p esen s udy, he i ing o he Mo¨ssbaue
spec a has been pe o med using he NORMOS p og am,
which allows a simul aneous i o se e al c ys alline spec a
wi h possible addi ion o an amo phous phase.
34
The as-
quenched alloy consis s o a b oad sex e ypical o amo -
phous phase (Fig. 9). The alloy emains in ully amo phous
s a e only up o he annealing empe a u e o 658 K, clea
e idence o he onse o c ys alliza ion was obse ed a e
annealing a 723 K (Fig. 9). The Mo¨ssbaue spec a o he
alloy in as-quenched s a e as well as a e annealing (up o
he empe a u e o 723 K) we e analyzed using NORMOS
(DIST) p og am, in e ms o a dis ibu ion o hype ine ields
ep esen ing he dis ibu ion o local en i onmen a ound he
Fe a oms. In he as quenched s a e, he Mo¨ssbaue spec um
has been i ed closely by he a e age magne ic hype ine
ield (hB
h
i) alue o 23.8 60.2 T o an amo phous sex e .
Upon annealing, he hB
h
i alue inc eases, eaching a alue
o 24.2 60.1 T a 723 K. This sugges s an inc ease in opo-
logical o de ing in he sys em, which co obo a es he SR-
XRD esul s. Figu e 10 p esen s esul an hype ine ield dis-
ibu ion o he alloy in he amo phous phase (up o 658 K)
and upon e olu ion o he nanoc ys alline phase (a 723 K).
The Hype ine ield dis ibu ion in he amo phous phase
consis s o wo b oad humps: A b oad hump wi h a maxi-
mum o hB
h
ia a ound 25 T and a smalle hump wi h a max-
imum o hB
h
ia ound 10 T. The smalle hump ep esen s he
Fe a oms ha ing Nb nea es neighbo s (NN). I is known ha
he p esence o Nb in he i s coo dina ion shell o Fe signi -
ican ly educes he hype ine ield o Fe a oms.
35
In he
amo phous s a e o he alloy P (hB
h
i) o he peaks a ound
25 T and a ound 10 T dec ease wi h annealing empe a u e
(Fig. 10). These changes co espond o he elemen s edis-
ibu ion in o ally amo phous alloy du ing he s uc u al
elaxa ion. Since Mo¨ssbaue measu emen shows only he
nea es en i onmen o Fe a oms, his spa ial dis ibu ion o
elemen s du ing composi ional luc ua ion can be in e p e ed
as a dec ease in he numbe o Fe-Fe NN as well as Fe-Nb
NN. This sugges s ha bo h he on-si e momen (Fe-Fe) and
he su ounding momen s (Fe-Nb) a e dec easing wi h
inc ease in annealing empe a u e. Addi ionally, o de ing in
he peaks a 25 T and 10 T is clea ly seen by he dec ease in
he wid h o hB
h
idis ibu ion wi h annealing empe a u e.
Upon annealing a 723 K, an addi ional hump a ound 34 T is
clea ly seen, which gi es a signa u e o he onse o o de ing
o he nanoc ys alline a0-FeCo phase. XRD and DSC meas-
u emen s also suppo his obse a ion.
The Mo¨ssbaue spec a o he alloys annealed a and
abo e 723 K show clea e idence o he c ys alliza ion
(Fig. 9). The e o e, he de ail i ing o he spec a a e c ys-
alliza ion was done using NORMOS (SITE) by conside ing
wo o e lapping sex e s: a sha p sex e co esponding o he
bcc-FeCo nanoc ys alline phase and a ela i ely b oad sex e
indica ing he emaining amo phous phase. I may be no ed
ha , in o de o ge bes i ing in c ys alline s a e o he
alloy, an addi ional double co esponding o Nb- ich non
magne ic phase was also included in he i ing model o
alloys annealed a and abo e 773 K. E idence o he o ma-
ion o such non magne ic nioba e phase was also obse ed
a e annealing a 773 K in ea lie s udies in he nanoc ys al-
lisa ion s age.
36
The i ing o he Mo¨ssbaue spec a a e annealing a
773 K sugges s ha nea ly 46% o Fe esides in he amo -
phous s a e. The p esence o he hype ine ield componen s
o 34.5 60.1 T shows he p esence o bcc-FeCo nanoc ys al-
line phase.
15
The olume ac ion o he non-magne ic com-
ponen is 14.8% wi h he quad upole spli ing o
1.56 60.05 mm/s. I may be no ed ha he line wid hs o he
quad upole double as ob ained om he i ing is e y la ge;
-8 -6 -4 -2 0 2 4 6 8
T ansmission (a b. uni s)
Veloci y (mm/s)
As-quenched
573 K
723 K
658 K
773 K
823 K
873 K
973 K
923 K
FIG. 9. Mo¨ssbaue spec a along wi h he i ings o he Fe
40.5
Co
40.5
Nb
7
B
12
alloy as a unc ion o inc easing annealing empe a u e.
5 1015202530354045
0.000
0.008
0.016
p is ine
573 K
658 K
723 K
P (B
HF
)
A e age B
HF
(T)
Amo phous s a e
FIG. 10. Hype ine ield dis ibu ion o Fe
40.5
Co
40.5
Nb
7
B3
12
alloy up o he
annealing empe a u e o 723 K.
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his sugges s ha Nb- ich phase is in a diso de ed s a e. This
diso de esul s in he dis ibu ion o quad upole spli ing.
Fu he annealing a highe empe a u es o 823 K and
873 K causes he specimen o consis o FeCo nanoc ys al-
line phase wi h a c ys alline ac ion o 42% and 47%,
espec i ely. Howe e , he spec um has been bes i ed
wi h c ys alline sex e s ha ing in e nal magne ic ield hB
h
i
o 34.6 60.1 and 34.5 60.1 T, espec i ely. The olume
ac ion o he non-magne ic componen was also ound o
be inc easing and eaches o 18.4% a e annealing a 873 K.
On he o he hand, i s quad upole spli ing dec eased o
0.71 60.04 mm/s. A e annealing a 923 K, he spec um
was bes i ed wi h hB
h
i alue o 34.2 60.1 T, co espond-
ing o FeCo nanoc ys alline phase, wi h inc eased c ys alline
ac ion o 54%. The olume ac ion o non-magne ic
componen becomes 19%, wi h quad upole spli ing o
0.70 60.02 mm/s.
Annealing a a empe a u e o 973 K esul s in he com-
ple e c ys alliza ion o he alloy. The bes i ing o he spec-
um has been ob ained wi h hB
h
io 34.3 60.1 and
28.2 60.1 T co esponding o FeCo and (FeCo)
23
B
6
, phases,
espec i ely,
22,37
no ace o any emaining amo phous ma-
ix was obse ed. Howe e along wi h nanoc ys alline Fe-
Co phase and bo ide phase, he p esence o non-magne ic
phase was s ill obse ed wi h olume ac ion o 16.5%
and quad upole spli ing o 0.53 60.07 mm/s. Dec ease o
quad upole spli ing wi h annealing empe a u e indica ed
possible o de ing o he Nb- ich non-magne ic phase which
can be a ibu ed o (FeCo)
3
Nb phase.
36
Fu he mo e, he A23 pa ame e ( he a ea a io o he
second and hi d lines o he Mo¨ssbaue spec a) gi es in o -
ma ion abou he o ien a ion o he magne ic momen . I was
ound ha he A23 pa ame e o as-quenched alloy is
2.6 60.1, which sugges s ha o ien a ion o spins is no an-
dom a he hey ha e some p e e ence o he in-plane o ien-
a ion. The A23 pa ame e dec eases wi h annealing and
becomes 1.2 60.1 upon annealing a 923 K, which indica es
ha he o ien a ion o spins is p e e en ially ou -o plane.
Upon u he annealing a 973 K, A23 pa ame e becomes
almos 2.0 60.1, which shows ha spins a e andomly o i-
en ed. Thus, upon annealing, magne ic momen s a e chang-
ing hei o ien a ion om in-plane o ou -o -plane o
andom.
38
I may be no ed ha s udied alloy exhibi s ong
pe pendicula magne ic aniso opy in he annealing empe a-
u e ange o 723 K-923 K ( i s ans o ma ion s age). In he
men ioned empe a u e ange, he alloy has peculia wo
phase mic os uc u e consis ing o FeCo nano-c ys als and
he emaining amo phous phase, as o he wise, spins a e o i-
en ed ei he in-plane o andom.
The o de ed a0-FeCo phase has lowe alues o hB
h
ias
compa ed o diso de ed a-FeCo phase (33.6 T and 35.7 T,
espec i ely).
15,29
In he p esen case, hB
h
i alue o he
nanoc ys alline FeCo phase is anging om 34.2 T o
34.6 T. I is clea ha low ield con ibu ions (close o 33 T)
a e p edominan , as is ound in he FeCo a omically o de ed
s uc u e.
28
In he second c ys alliza ion s age (973 K), as depic ed by
Mo¨ssbaue measu emen s, he coexis ence o o de ed a0-FeCo
nanoc ys alline so magne ic phase and ha d magne ic
(FeCo)
23
B
6
,phasehasalsobeencon i medwi hSR-XRD
measu emen s. Mo¨ssbaue measu emen s also suppo he
p esence o Nb ich non-magne ic phase in nano-c ys alline
specimens annealed a he empe a u e g ea e han 723 K.
Howe e , he p esence o he same has no been de ec ed
h ough XRD measu emen up o 923 K. This may be a ib-
u ed o smalle c ys alli e size and/o high deg ee o diso de .
39
I is impo an o no e ha he wid h o hype ine ield dis ibu-
ion o Mo¨ssbaue spec um depends mainly on he chemical
sho ange o de ; hus, i can be u ilized o iden i y phases
whose dimensions a e oo small o XRD measu emen s.
40
Thus in concu ence wi h anomalous di ac ion measu e-
men s, Mo¨ssbaue measu emen s also suppo s he nanoc ys-
alline phase in Fe
40.5
Co
40.5
Nb
7
B
12
alloy has an a omically
o de ed a0-FeCo (B2) s uc u e.
41
E. The momagne ic measu emen s
TMG measu emen s we e pe o med o de ec he c ys-
alliza ion o e omagne ic phases in Fe
40.5
Co
40.5
Nb
7
B
12
alloy. Figu e 11 shows he empe a u e dependence o he
low ield (20 mT) magne iza ion. Fo compa ison, DSC plo
is also included in he same igu e. Upon hea ing, he e is a
i s dec ease in magne iza ion (M) due o app oaching he
Cu ie empe a u e (T
c
) o he ini ial amo phous phase. How-
e e , i does no all o ze o because he nanoc ys allisa ion
o bcc-(Fe, Co) phase akes place be o e T
c
is eached (as
e idenced by he DSC eco d and he e olu ion o he XRD
spec a). The onse o nanoc ys allisa ion p oduces an
inc ease in magne iza ion due o he appea ance o he e o-
magne ic bcc-(Fe, Co) phase, which has a la ge Cu ie em-
pe a u e. The o e lapping o hose wo compe ing e ec s
(dec ease in M due o he Cu ie empe a u e o he amo -
phous phase and inc ease in M due o he o ma ion o he
e omagne ic phase) al e s he shape o he M (T) cu e,
which dec eases mo e slowly han a ypical e o-
pa amagne ic ansi ion. The inc ease o he c ys alline ac-
ion o he nanophase p oduces a la ge inc ease in M. A e
eaching a maximum, magne iza ion dec eases u he . This
dec ease could be ei he due o a Cu ie ansi ion o due o
u he c ys alliza ion o he alloy, whe e he exis ing bcc-
600 700 800 900 1000 1100
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
-2
-1
0
1
2
3
4
M (a b. uni s)
Tempe a u e (
K
)
Hea low (mW)
FIG. 11. Tempe a u e dependence o he low ield magne iza ion o as–
quenched Fe
40.5
Co
40.5
Nb
7
B
12
alloy (upon hea ing) along wi h DSC scan up
o i s c ys alliza ion s age.
113518-8 Gup a e al. J. Appl. Phys. 111, 113518 (2012)
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