In luence o La and Ce addi ions on he magne ocalo ic e ec
o Fe–B–C -based amo phous alloys
J. Y. Law,1V. F anco,2and R. V. Ramanujan1,a兲
1School o Ma e ials Science and Enginee ing, Nanyang Technological Uni e si y, Singapo e 639798
2Dp o. Física de la Ma e ia Condensada, ICMSE-CSIC, Uni e sidad de Se illa, P.O. Box 1065,
41080 Se illa, Spain
共Recei ed 14 Ma ch 2011; accep ed 14 Ap il 2011; published online 10 May 2011兲
The magne ic en opy change 共⌬SM兲, empe a u e o peak ⌬SM共Tpk兲and e ige an capaci y 共RC兲
in Fe共RE兲80B12C 8共RE=La, Ce, o Gd兲alloys we e s udied. Inc easing La, Ce, and Gd con en
led o ela i ely cons an , dec ease, and inc ease in Tpk, espec i ely. Bo h he phenomenologically
cons uc ed uni e sal cu e o ⌬SMand ield dependence powe laws demons a ed ha hese
alloys exhibi ed simila c i ical exponen s a Cu ie empe a u e. Wi h 5% Ce added o Fe80B12C 8,
Tpk could be uned nea oom empe a u e wi h ela i ely cons an peak ⌬SM.Fe
79B12C 8La1
exhibi ed enhanced RC compa ed o Gd5Si2Ge1.9Fe0.1. The unable Tpk and enhanced RC a e needed
in ac i e magne ic egene a o s. © 2011 Ame ican Ins i u e o Physics.关doi:10.1063/1.3589353兴
Magne ic e ige a ion 共MR兲o e s a compe i i e al e -
na i e o con en ional apo comp ession e ige a ion sys-
ems due o i s high ene gy e iciency and en i onmen al
iendliness.1–3I employs he magne ocalo ic e ec 共MCE兲,
which is ela ed o he e e sible empe a u e change in a
magne ocalo ic ma e ial 共MCM兲subjec ed o a ying mag-
ne ic ield unde adiaba ic condi ions.1The Cu ie empe a-
u e 共TC兲o MCM plays a signi ican ole in magne ocalo ic
s udies because MCE peaks nea TC. Gadolinium, a well-
known MCM, exhibi s la ge MCE wi h a second o de mag-
ne ic ansi ion 共SOMT兲a TCnea oom empe a u e 共RT兲.
Howe e , i s high cos , poo co osion esis ance, and e-
s ic ed a ailabili y necessi a e he de elopmen o MCM o
nea RT MR. An ideal MCM should be low cos and exhibi
good e ige an capaci y 共RC兲and peak magne ic en opy
change 共兩⌬SM
pk兩兲 wi h li le hys e esis. I on-based amo phous
alloys ul ill such equi emen s. They o e low magne ic
hys e esis, high elec ical esis i i y, enhanced co osion e-
sis ance, good mechanical p ope ies, and unable TCby
composi ion a ia ion.4–6In addi ion, he elemen s in ol ed
a e abundan and ab ica ion cos s a e easonable, making
hem highly compe i i e. Fe80C 8B12 amo phous alloys ex-
hibi p omising MCE nea RT, C addi ions enhance he co -
osion esis ance o he alloy.7Gd addi ions o his alloy ha e
been s udied p e iously8wi h he aim o uning he TCo he
alloy. Fe79B12C 8Gd1alloy displayed enhanced 兩⌬SM
pk兩
共⬃33% la ge han Fe80B12C 8兲and RC alues 关⬃29% la ge
han Gd5Si2Se1.9Fe0.1 共Re . 9兲兴. These indings sugges ha
s udies o he e ec o a e ea hs 共REs兲addi ions on he
MCE o Fe-based amo phous alloys would be use ul. The
ype o RE addi ions o ansi ion me als 共TMs兲, such as Fe,
in luences he ne magne ic momen o he alloys signi i-
can ly: Gd and hea y RE con ibu e o e imagne ism while
ligh RE con ibu e o e omagne ism, which gene ally e-
sul s in a la ge ne magne ic momen han he o me .10 The
magne ism in such alloys depends on he na u e o coupling
be ween he RE and TM momen s. As he 4 -5delec on
exchange in e ac ion a he RE si e is e omagne ic, he an-
i e omagne ic 5d共RE兲-3d共TM兲elec on in e ac ions esul
in e omagne ic coupling o ligh RE o TM momen s and
ice e sa o hea y RE.11 This p esen wo k shows ha La,
Ce, and ou p e iously s udied Gd addi ions o Fe–B–C
amo phous alloys in luence he empe a u e o ⌬SM
pk 共Tpk兲
di e en ly.
Alloys wi h nominal composi ion Fe80−xB12C 8Lax
共x=0, 1, 5, 10, and 15兲and Fe80−yB12C 8Cey共y=2, 5, 10,
and 15兲we e mel spun in o ibbons. The ibbons a e de-
no ed by hei 共a兲La con en as La1, La5, La10, and La15,
and 共b兲Ce con en as Ce2, Ce5, Ce10, and Ce15. The amo -
phici y o he ibbons was con i med by x- ay di ac ion.
Magne ic p ope ies we e measu ed by Lakesho e 7407 i-
b a ing sample magne ome e o magne ic ields up o 15
kOe. The magne ic en opy change 共⌬SM兲due o he a ia-
ion in applied magne ic ield 共H兲was de e mined om
⌬SM=兰0
H共
⳵
M/
⳵
T兲HdH. RC is calcula ed in wo ways in his
s udy: 共a兲RCFWHM: he p oduc o ⌬SM
pk imes he ull em-
pe a u e wid h a hal maximum o he peak 共RCFWHM
=⌬SM
pk⫻
␦
TFWHM兲, and 共b兲RCAREA: nume ical in eg a ion o
he a ea unde he ⌬SM共T兲cu es, using he ull empe a u e
wid h a hal maximum o he peak as he in eg a ion limi s.
The composi ional dependence o 兩⌬SM
pk兩,T
pk, and
RCFWHM a e shown in he main panel o Fig. 1. Fo bo h La
and Ce se ies, 兩⌬SM
pk兩 alues emains ela i ely cons an o
RE con en up o 5 a . % and p og essi ely dec eases o
highe concen a ions. The 兩⌬SM
pk兩 o Fe80−xRExB12C 8共RE
=La o Ce; x=1–5 a . %兲alloys compa e a o ably wi h
he base Fe80B12C 8amo phous alloy.7Fo highe Gd con-
en , he dec ease in 兩⌬SM
pk兩 o he Gd alloy se ies was la ge
han hose o he La and Ce se ies 共Gd con en ⱖ3 a . %兲.
⌬SMhas been shown o be co ela ed wi h he magne ic mo-
men o he ma e ial in o he alloy sys ems.8,12,13 To in es i-
ga e whe he such a ela ionship holds be ween 兩⌬SM
pk兩
and he magne ic momen o Fe80−xB12C 8Laxand
Fe80−yB12C 8Ceyamo phous alloys, he empe a u e depen-
dence o magne iza ion was measu ed below TC. The low
empe a u e spon aneous magne iza ion 共M0兲was ob ained
by he linea ex apola ion o M共T3/2兲plo s. The expe imen-
al 兩⌬SM
pk兩 alues we e plo ed as a unc ion o M0in he inse
a兲Au ho o whom co espondence should be add essed. Elec onic mail:
[email p o ec ed]. Tel.: ⫹65 67904342. FAX: ⫹65 67909081.
APPLIED PHYSICS LETTERS 98, 192503 共2011兲
0003-6951/2011/98共19兲/192503/3/$30.00 © 2011 Ame ican Ins i u e o Physics98, 192503-1
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o Fig. 1,a共i兲 o bo h alloy se ies as well as he p e iously
s udied Fe80−zB12C 8Gdz共z=1–11 a . %兲alloys.8兩⌬SM
pk兩in-
c eases wi h inc easing M0, e idencing he abo emen ioned
linea co ela ion be ween 兩⌬SM
pk兩and M0. This also a ibu es
o he composi ional dependence o 兩⌬SM
pk兩. As La a oms do
no exhibi magne ic momen ,11 he end o 兩⌬SM
pk兩dec eas-
ing wi h highe La concen a ion in La alloys e lec dilu ion
o he magne ic coupling be ween he Fe momen s. The M0
alues o he Ce alloy se ies we e obse ed o be lowe han
he co esponding La alloys in Fig. 1,a共ii兲. The Ce ion in
Fe–Ce alloys was epo ed o exhibi e a alen alence s a e
unlike o he i alen RE ions.14 Hence, he localized 4 elec-
on o Ce a om can be easily displaced o he 5dconduc ion
band. This esul s in a u he dis inc hyb idiza ion o 5d
s a es wi h 3ds a es in Fe–Ce alloys, which can lead o lowe
magne iza ion in Fe–Ce alloys compa ed o o he amo phous
ligh RE-Fe alloys.15,16 Fo he Gd alloy se ies, he la ge
magne ic momen o Gd compa ed o he o he RE in es i-
ga ed in his s udy led o he highes 兩⌬SM
pk兩 alue 共1 a . %
Gd兲. I s educed 兩⌬SM
pk兩 o inc easing Gd addi ions is due o
he an ipa allel coupling be ween Gd and Fe momen s, lead-
ing o educed M0 o highe Gd con en .
The empe a u e o he peak magne ic en opy change
共Tpk兲can be conside ed as Tc o low H.17 Tpk shows li le
a ia ion as La con en inc eases, consis en wi h ea lie e-
po s in amo phous Fe–La bina y alloys.18 The p esence o
C and B in ou alloys displaces TC o highe empe a u es
compa ed o he li e a u e.18–20 In con as , Tpk educes as Ce
concen a ion inc eases. The Ce alloy se ies displays lowe
Tpk alues compa ed o he La alloy se ies.21
The magne ic o de ing empe a u es o Gd and Ce al-
loys we e he highes and lowes , espec i ely.22 Ce was e-
po ed o adop he e a alen s a e in Ce–Fe alloys, which
can lead o educ ion in he Fe–Fe dis ance, which in u n
educes TC,23 and hus hese alloys exhibi lowes TCcom-
pa ed o o he ligh RE alloys.22 Gd has been epo ed o
display he la ges TCamong all RE,22,23 which led de
Gennes o co ela e his maximum wi h he maximal alue o
4 spin in Gd.24 In addi ion, Tpk in he La se ies showed li le
a ia ion wi h La con en compa ed o hose o Ce and Gd
con aining alloys. In con as , Ce alloys show a mono onic
dec ease in Tpk wi h inc easing Ce con en . Unlike he La
and Ce se ies, Tpk was obse ed o inc ease wi h highe Gd
addi ions.25,26 RCFWHM educed wi h inc easing RE con en ,
wi h he Gd alloy se ies displaying he la ges dec ease com-
pa ed o he La and Ce alloy sys ems. Fo Ce15, he dec eas-
ing end o RC shows a la ge nega i e slope compa ed o
ha o he La15 alloy. To s udy his educ ion in RCFWHM,
he composi ional dependence o ull empe a u e wid h a
hal maximum 共
␦
TFWHM兲o 兩⌬SM
pk兩was plo ed 关inse o Fig.
1共c兲兴. Fo RE=15 a . %:
␦
TFWHM inc eased o he La15 al-
loy while he Ce15 alloy showed a la ge educed
␦
TFWHM
among he Ce alloy se ies. Fo La alloy se ies,
␦
TFWHM did
no signi ican ly change wi h La concen a ion. On he o he
hand,
␦
TFWHM dec eased wi h inc easing Ce concen a ion.
The dec ease in RC o he La alloy se ies could be a ibu ed
o he educ ion in 兩⌬SM
pk兩共RC being p opo ional o 兩⌬SM
pk兩
and
␦
TFWHM兲since 兩⌬SM
pk兩gene ally plays a dominan ole in
RC maximiza ion o SOMT ma e ials.27 Fo he Ce alloy
se ies, he educed 兩⌬SM
pk兩and
␦
TFWHM con ibu es o a much
lowe RC alue, e.g., in he Ce15 alloy. Fo he Gd se ies, he
la ge dec easing end o RC could be a ibu ed o he la ge
educ ion in 兩⌬SM
pk兩wi h Gd addi ion.
Li e a u e epo s o he p ope ies o MCM a e usually
published a he maximum a ailable magne ic ield in indi-
idual labo a o ies. To compa e di e en li e a u e alues,
he ield dependence s udies o ⌬SM
pk and RC should be
known. The ield dependence o magne ic en opy change
can be exp essed as ⌬SM
pk⬀Hn, alida ed expe imen ally in
se e al so magne ic amo phous alloys and some RE-based
c ys alline MCM.17 The exponen nis ield in a ian a TCo
Tpk.17 The ield dependence o RC can also be ep esen ed by
a powe law exp ession: RCFWHM⬀HN. Exponen s n 共and N兲
should ha e simila alues o a gi en alloy se ies since hey
a e con olled by he c i ical exponen s o he alloy se ies.
As an example, ⌬SM
pk共H兲and RC共H兲 o he La5 and Ce5
alloys a e p esen ed in he inse s o Fig. 2. The good i s
shown aid he de e mina ion o he exponen s n and N. Fo
he La alloys: n=0.79⫾0.01 and N=1.20⫾0.01; and Ce al-
loys: n=0.77⫾0.03 and N=1.20⫾0.01. These alues a e
close o hose ob ained o Gd alloys 共n=0.75⫾0.01 and N
=1.16⫾0.01兲.8Bo h RCFWHM and RCAREA ha e been p e-
dic ed o scale wi h ield wi h he same alue o exponen ,17
in good ag eemen wi h ou expe imen al esul s. When
兩RCAREA兩 o he La1 and La5 alloy a e ex apola ed o H
=50 kOe, alues o 386 J kg−1 and 356 J kg−1, espec-
i ely, a e ob ained, which a e up o ⬃9% highe han he
well-known MCM—Gd5Si2Ge1.9Fe0.1.9Fo Ce2 alloys, i s
兩RCAREA兩yield 367 J kg−1 when ex apola ed o 50 kOe,
FIG. 1. 共Colo online兲Composi ional dependence o 共a兲兩⌬SM
pk兩,共b兲Tpk, and
共c兲RCFWHM o he as-spun ibbons a H=11 kOe. 共1a兲inse : 共i兲spon ane-
ous magne iza ion dependence o 兩⌬SM
pk兩and 共ii兲composi ional dependence
o M0.共1c兲inse : composi ional dependence o
␦
TFWHM.
192503-2 Law, F anco, and Ramanujan Appl. Phys. Le . 98, 192503 共2011兲
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which shows ⬃3% imp o emen o e Gd5Si2Ge1.9Fe0.1.9A
phenomenological uni e sal cu e o ⌬SMis used o ex-
apola e magne ocalo ic p ope ies o magne ic ields and/o
empe a u es which a e inaccessible in di e en labo a o ies.
This aids he pe o mance e alua ion o di e en MCM. I s
cons uc ion equi es he no maliza ion o ⌬SM共T兲wi h e-
spec o hei peaks:17 ⌬S⬘=⌬SM/⌬SM
pk and escaling he em-
pe a u e axis
␪
using wo e e ence empe a u es 共T 兲such
ha ⌬SM共T 兲/⌬SM
pk=0.6. The escaled ⌬SM共T兲cu es o La
and Ce alloys a e p esen ed in he main panel o Fig. 2. The
no malized ⌬SMcu es collapse nicely on o a single cu e
o each alloy se ies, con i ming ha hey exhibi SOMT,
ha he uni e sal cu e is applicable o hese alloys and ha
hei c i ical exponen s should be he same.
In summa y, addi ions o La and Ce o Fe–B–C amo -
phous alloys led o di e en in luences on Tpk. Wi h inc eas-
ing RE con en , Tpk dec eases o Fe80−yB12C 8Ceybu in-
c eases o Fe80−zB12C 8Gdz. La addi ions ha e li le e ec
on Tpk. Fo x=1 and 5 a . % in Fe80−xB12C 8Laxand
Fe80−xB12C 8Cexamo phous alloys, Tpk can be uned nea
RT wi h 兩⌬SM
pk兩compa able o he base Fe80B12C 8alloy.
Bo h ⌬SM
pk共H兲and RC共H兲ag ees wi h heo e ical p edic ions
o a powe law dependence, yielding exponen s as 0.79 and
1.20, espec i ely, o he La alloy se ies and 0.77 and 1.20,
espec i ely, o he Ce alloys. These a e in good ag eemen
wi h he p e ious esul s o he Gd alloy se ies.
Fe79B12C 8La1alloys exhibi enhanced RC compa ed o he
well-known MCM Gd5Si2Ge1.9Fe0.1.
This wo k was suppo ed by he U.S. AOARD 共G an
No. AOARD-08-4018兲, p og am manage , D . R. Ponnap-
pan, by he Spanish Minis y o Science and Inno a ion and
EU FEDER 共P ojec No. MAT 2010-20537兲, he PAI o he
Regional Go e nmen o Andalucía 共P ojec No. FQM-
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FIG. 2. 共Colo online兲Uni e sal cu es o Fe80−xB12C 8RExwhe e RE
=La o Ce. Inse : ield dependence o ⌬SM
pk 共䊐兲,RC
FWHM 共䊊兲, and RCAREA
共䉭兲 o 共a兲La5 and 共b兲Ce5 alloys. Lines a e i s o he powe law
exp essions.
192503-3 Law, F anco, and Ramanujan Appl. Phys. Le . 98, 192503 共2011兲
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