The in luence o Co addi ion on he magne ocalo ic e ec o Nanope m- ype
amo phous alloys
V. F anco, J. S. Blázquez, and A. Conde
Ci a ion: Jou nal o Applied Physics 100, 064307 (2006); doi: 10.1063/1.2337871
View online: h p://dx.doi.o g/10.1063/1.2337871
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The in luence o Co addi ion on he magne ocalo ic e ec
o Nanope m- ype amo phous alloys
V. F anco, J. S. Blázquez, and A. Condea兲
Depa amen o de 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 3 Ma ch 2006; accep ed 21 June 2006; published online 22 Sep embe 2006兲
The e ec o Co addi ion on he magne ocalo ic e ec o amo phous alloys wi h Nanope m- ype
composi ion has been s udied o empe a u es abo e oom empe a u e. Co addi ion p oduces an
inc ease in he maximum magne ic en opy change and a shi o i s associa ed empe a u e o highe
empe a u es. The maximum e ige an capaci y 共RC兲 alue ob ained in his s udy is 82 J kg−1 o
a maximum applied ield H=15 kOe. This alue is ⬃30% la ge han ha o a Mo-con aining
Fineme - ype alloy measu ed unde he same expe imen al condi ions. Howe e , he RC o he
alloys, when calcula ed om empe a u es co esponding o he hal -maximum en opy change
alue, de e io a es wi h he p esence o Co in he alloy. The ield dependence o he magne ic
en opy change has also been analyzed, showing a powe dependence o all he magne ic egimes
o he samples. This ield dependence a he Cu ie empe a u e de ia es om mean ield
p edic ions. © 2006 Ame ican Ins i u e o Physics.关DOI: 10.1063/1.2337871兴
INTRODUCTION
The magne ocalo ic e ec 共MCE兲, epo ed by Wa bu g
in 1881,1consis s in he empe a u e change o a magne ic
ma e ial upon he applica ion o a magne ic ield. When mag-
ne ized, he en opy o he spin subsys em is dec eased and,
unde adiaba ic condi ions, he ans e o ene gy o he la -
ice p o okes he hea ing o he ma e ial. Con e sely, he
adiaba ic demagne iza ion o he ma e ial causes i s cooling,
an e ec ha has been employed o eaching empe a u es
below 1 K since 1933.2
MCE phenomenon is no new, and he e we e p oposals
o employing i a empe a u es close o oom empe a u e
since 1976.3In 1998 a p o o ype was e icien ly es ed o
oom- empe a u e magne ic e ige a ion.4This long delay in
he applica ion o he MCE a high empe a u es was no due
o concep ual di icul ies, bu o echnological ones, he se-
lec ion o adequa e ma e ials being among hem.
To display a signi ican MCE esponse, a ma e ial needs
o exhibi an app eciable empe a u e dependence o magne-
iza ion in he applica ion empe a u e ange. The e o e, o
cooling a empe a u es a ound 1 K, pa amagne ic ma e ials
can be used as hei magne ic esponse inc eases when ap-
p oaching 0 K. Howe e , hei esponse is negligible a em-
pe a u es close o oom empe a u e. In o de o ob ain ma-
e ials wi h a no iceable empe a u e dependence o
magne iza ion a highe empe a u es, e omagne ic ma e i-
als can be used. When he Cu ie empe a u e o he ma e ial
is app oached, he e omagne ic-pa amagne ic ansi ion
causes a peak in he magne ic en opy change associa ed
wi h he magne iza ion/demagne iza ion o he ma e ial. As
he Cu ie empe a u e o Gd is close o oom empe a u e
共294 K兲and i s magne ic momen is la ge, his elemen was
he ma e ial o choice o de eloping he ini ial oom-
empe a u e p o o ypes.3,4 The e o s o inding ma e ials
which can be employed as high empe a u e magne ic e ig-
e an s a e no u ile, because e ige a ion based on MCE is
ene ge ically mo e e icien han ha o con en ional gas
comp ession-expansion e ige a o s and mo e en i onmen-
al iendly as nei he ozone-deple ing no global-wa ming
ola ile e ige an s a e equi ed. The e o e, cu en ly he e
is an in ensi e esea ch in his ield,5–7 wi h wo main objec-
i es: he maximiza ion o ma e ial p ope ies and he educ-
ion o ma e ial cos . In his espec , he peak en opy change
共兩⌬SM
pk兩兲 has been maximized wi h he so-called gian MCE
共Re . 8兲and gian in e se MCE,9while cos educ ion is
being in es iga ed by using ansi ion me al based alloys in-
s ead o a e ea h based ma e ials.10 In pa icula , he e is a
g owing in e es in s udying he applicabili y o so mag-
ne ic amo phous alloys as magne ic e ige an s11–15 due o
hei educed magne ic hys e esis 共 i ually negligible兲, en-
hanced elec ical esis i i y, and unable Cu ie empe a u e.
In he case o bulk amo phous alloys,16,17 ou s anding me-
chanical p ope ies a e also exhibi ed. All hese cha ac e is-
ics a e bene icial o a success ul applica ion o he ma e ial.
The aim o his wo k is o analyze MCE o so magne ic
amo phous alloys o he Nanope m amily, aking in o con-
side a ion he in luence o Co addi ion on he e ige an ca-
paci y o he ma e ial, and o s udy he ield dependence o
he magne ic en opy change. As he magne ic momen and
Cu ie empe a u e o Fe based amo phous alloys depend on
Co addi ion, i could be expec ed ha i will also ha e an
in luence on MCE.
EXPERIMENT
Amo phous ibbons 共⬃5 mm wide and 20–30
␮
m
hick兲o Fe83Z 6B10Cu1and Fe78Co5Z 6B10Cu1we e ob-
ained by mel spinning. The amo phous cha ac e o he
as-quenched alloys was checked by x- ay di ac ion. The
ield dependence o magne iza ion was measu ed in a Lake-
sho e 7407 ib a ing sample magne ome e using a maxi-
a兲Elec onic mail: [email p o ec ed]
JOURNAL OF APPLIED PHYSICS 100, 064307 共2006兲
0021-8979/2006/100共6兲/064307/4/$23.00 © 2006 Ame ican Ins i u e o Physics100, 064307-1
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mum applied ield H=15 kOe wi h ield s eps o 50 Oe, o
cons an empe a u es in he ange o 300–625 K wi h inc e-
men s o 10 K. P io o he measu emen s, he s ess o he
samples was elaxed by p eannealing hem a 700 K.
The MCE can be cha ac e ized by he magne ic en opy
change due o he applica ion o a magne ic ield H, which
can be e alua ed om he p ocessing o he empe a u e and
ield dependen magne iza ion cu es using a nume ical ap-
p oxima ion o he equa ion
⌬SM=
冕
0
H
冉
⳵
M
⳵
T
冊
H
dH,共1兲
whe e he pa ial de i a i e is eplaced by ini e di e ences
and he in eg a ion is pe o med nume ically.
In o de o compa e he pe o mance o di e en ma e-
ials, ei he he peak en opy change 兩⌬SM
pk兩o he e ige an
capaci y 共RC兲is used. The e ige a ion a low empe a u es
equi es a na ow empe a u e span o he e ige a ion cycle,
making 兩⌬SM
pk兩 he pa ame e o choice o compa ing low
empe a u e ma e ials, while high empe a u e e ige a ion
implies a wide empe a u e ange and, consequen ly, RC is
employed o compa ison. Acco ding o Wood and Po e ,18
he RC o a e e sible e ige a ion cycle ope a ing be ween
Thand Tc共 he empe a u es o he ho and cold ese oi s,
espec i ely兲is de ined as RC=⌬SM⌬T, whe e ⌬SMis he
magne ic en opy change a he ho and cold ends o he
cycle and ⌬T=Th−Tc. Mo eo e , hys e esis losses can be
aken in o accoun when e alua ing he e ige an ma e ial
by sub ac ing hem om he compu ed RC,19 making he
compa ison be ween ma e ials wi h di e en coe ci i ies
mo e s aigh o wa d. The op imal e ige a ion cycle is ha
which maximizes he RC.
RESULTS AND DISCUSSION
Tempe a u e dependence o he magne ic en opy
change
Figu e 1 shows he empe a u e dependence o he mag-
ne ic en opy change co esponding o an applied ield H
=15 kOe o he wo s udied samples. Co addi ion p oduces
an enhancemen in he empe a u e a which he maximum
en opy change akes place, in ag eemen wi h he in luence
o Co con en on he Cu ie empe a u e o he amo phous
phase 共TC
am兲 o hese alloys.20 I is wo h men ioning ha , in
con as o his beha io , amo phous alloys wi h la ge me -
alloid concen a ion exhibi a mono onous dec ease o TC
am
wi h inc easing Co con en .21–23 In he case o he s udied
alloys, Co addi ion leads o an inc ease o he 兩⌬SM
pk兩 alue,
unlike he obse ed beha io o he FeCoSiAlGaPCB alloy
se ies, wi h la ge me alloid con en .17 I has o be no ed ha
an es ima e o he e o in 兩⌬SM
pk兩is below 3%, which is
below he di e ences obse ed o bo h samples. The expla-
na ion o his in luence o he me alloid con en on TC
am and
兩⌬SM
pk兩should be asc ibed o he change in he local en i on-
men o Fe and Co a oms and i s e ec on he exchange
in e ac ion be ween a oms.23 The 兩⌬SM
pk兩 alue o he Co-
con aining Nanope m- ype alloy is ⬃50% la ge han ha o
a Mo-con aining Fineme - ype alloy, wi h a compa able TC
am,
measu ed unde he same expe imen al condi ions,14 while
he Co- ee Nanope m- ype alloy inc eases he peak en opy
change by ⬃31% wi h espec o he same Fineme - ype al-
loy. Compa ing wi h he Fe70B5C5Si3Al5Ga2P10 amo phous
alloy,17 he Co-con aining alloy p esen s a compa able alue
o 兩⌬SM
pk兩, wi h he ad an age o a peak empe a u e Tpk,
which is 100 K close o oom empe a u e o he alloy
s udied in he p esen wo k.
Field dependence o he magne ic en opy change
The magne ic en opy change no only depends on he
measu ing empe a u e bu also on he alue o he maximum
applied ield. Figu e 2 shows he combined ield and em-
pe a u e dependence o 兩⌬SM兩 o he wo s udied alloys. Fo
all empe a u es, he magne ic en opy change inc eases wi h
inc easing maximum applied ield H. The ield dependence
can be exp essed as
FIG. 1. 共Colo online兲Tempe a u e dependence o he magne ic en opy
change o a maximum applied ield o 15 kOe.
FIG. 2. 共Colo online兲Field and empe a u e dependences o he magne ic
en opy change o Fe83Z 6B10Cu1共bo om兲and Fe78Co5Z 6B10Cu1共 op兲.
064307-2 F anco, Blázquez, and Conde J. Appl. Phys. 100, 064307 共2006兲
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⌬SM⬀Hn,共2兲
whe e ndepends on he magne ic s a e o he sample. Fo
e omagne s abo e hei Cu ie empe a u e, he di ec in e-
g a ion o he Cu ie-Weiss law indica es ha n=2.5Howe e ,
o empe a u es below he Cu ie empe a u e no analy ical
exp ession is a ailable. Mo eo e , he in insic i e e sible
beha io o e omagne ic ma e ials has o be aken in o ac-
coun in o de o de i e a he modynamical model,24 a con-
side a ion which is specially impo an o ma e ials wi h
non-negligible hys e esis 共which is no he case in he p esen
s udy兲. Ne e heless, on he basis o a mean ield app oach,
he ield dependence o he magne ic en opy change a he
Cu ie empe a u e has been p edic ed o co espond o n
=2/3.25 In o de o de e mine he ield dependence o he
expe imen al 兩⌬SM兩da a o he di e en magne ic egions o
he s udied samples, a local exponen 16 can be calcula ed as
n=dln兩⌬SM兩
dln H.共3兲
Figu e 3 shows he empe a u e dependence o he local
exponen s o he Co- ee alloy o applied ields o 0.5, 1,
and 1.5 T. Some gene al ea u es o he cu es, also ul illed
o he Co-con aining alloy, a e wo h men ioning. In he
e omagne ic egime he local exponen is n⬇1. A he Cu-
ie empe a u e o he amo phous alloy, a dec ease in nis
obse ed. Howe e , i does no each 2/3, as p edic ed by
he mean ield app oach, bu dec eases only o ⬃0.74. Abo e
TC
am he local exponen inc eases up o n⬇2, as p edic ed by
he Cu ie-Weiss law. I should be ecalled ha his law is
accu a e o low ields and high empe a u es, which explains
he as e inc ease o n o smalle applied ields, as he high
empe a u e condi ion is achie ed a lowe empe a u es o
smalle applied ields. The inal inc ease in he exponen is
asc ibed o nume ical e o s, as he magne ic en opy change
is negligible a hese empe a u es.
The ield dependence o ⌬SMa Tpk o he Co- ee alloy
is also analyzed in Fig. 4 by ep esen ing ⌬SM
pk e sus ield
and i ing he cu e o a powe law 共equi alen esul s a e
ob ained o he Co-con aining alloy兲. The alue ob ained o
he exponen 共⬃0.76兲is compa able o he minimum in Fig.
3. This alue o he exponen , highe han he mean ield
p edic ions, could be due o local inhomogenei ies in he
amo phous alloy, causing a dis ibu ion o Cu ie empe a-
u es, al hough he amo phous cha ac e o he alloy can also
ha e an e ec . On he o he hand, disc epancies wi h mean
ield heo ies in he icini y o a ansi ion empe a u e can
be expec ed.
Re ige an capaci y
As p e iously men ioned, he compa ison be ween di -
e en ma e ials o high empe a u e magne ic e ige a ion
should be based on he e ige an capaci y. Figu e 5 shows
he e ige an capaci y o he s udied alloys as a unc ion o
he empe a u e o he cold ese oi , Tc, anging om oom
empe a u e up o Tpk o each alloy. As Tcsepa a es om Tpk,
he e ige an capaci y o he ma e ial inc eases. An op imal
e ige a ion cycle can be ound o he Co-con aining alloy
in he expe imen al empe a u e ange, as e idenced by a
maximum in RC. The maximum RC alues ob ained in his
s udy a e 77 and 82 J/kg o he Co- ee and Co-con aining
alloys, espec i ely, indica ing a supe io pe o mance o he
Co-con aining alloy o e ige a ion cycles wi h Tcabo e
oom empe a u e. Howe e , he shape o he cu e o he
Co- ee alloy sugges s a maximum RC below oom empe a-
u e o his alloy.
Ins ead o compa ing he maximum ob ained RC alues,
i we compa e he RC alues o e ige a ion cycles wi h
empe a u es co esponding o hal o 兩⌬SM
pk兩共i.e., he em-
pe a u e span o he cycle co esponds o he wid h a hal -
FIG. 3. 共Colo online兲Tempe a u e dependence o he local exponen de e -
mining he ield dependence o he magne ic en opy change o he
Fe83Z 6B10Cu1alloy o h ee di e en maximum applied ields. The lines
a e a guide o he eyes.
FIG. 4. 共Colo online兲Field dependence o he peak en opy change o he
Fe83Z 6B10Cu1alloy. The line is he i ing o he da a.
FIG. 5. 共Colo online兲Dependence o he e ige an capaci y on he em-
pe a u e o he cold end o he e ige a ion cycle o he Fe83Z 6B10Cu1and
Fe78Co5Z 6B10Cu1alloys.
064307-3 F anco, Blázquez, and Conde J. Appl. Phys. 100, 064307 共2006兲
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maximum兲, he conside a ion o he Co-con aining alloy as
he one wi h a be e pe o mance no longe holds. In his
case RC alues a e 71 and 63 J/kg o he Co- ee and Co-
con aining alloys, espec i ely. This is in ag eemen wi h he
p e ious sugges ion o an op imal cycle o he Co- ee alloy
wi h a cold end below oom empe a u e. These alues a e
compa able o ecen esul s on he magne ocalo ic e ec o
Co–C con aining Nanope m- ype alloys.15
Figu e 6 p esen s he ela ionship be ween Thand Tc o
cycles which p oduce he maximum RC o a gi en Tc. Fo
he Co-con aining alloy, he op imal e ige a ion cycle co -
esponds o Th⬇531 K and Tc⬇325 K, while o he Co-
ee alloy he maximum ob ained RC co esponds o Th
⬇440 K and Tc⬇308 K.
The maximum RC alue measu ed in his wo k a o -
ably compa es o he p e iously men ioned Fineme - ype and
Fe70B5C5Si3Al5Ga2P10 amo phous alloys, being ⬃30%
la ge in he p esen case.
CONCLUSIONS
The e ec o Co addi ion on he magne ocalo ic e ec o
Fe83Z 6B10Cu1and Fe78Co5Z 6B10Cu1amo phous alloys has
been s udied. The empe a u e a which he maximum mag-
ne ic en opy change akes place is shi ed o highe empe a-
u es wi h Co addi ion, simul aneously inc easing he alue
o his peak en opy change. Howe e , he e ige an capac-
i y o he alloys, when calcula ed om he hal -maximum
empe a u es, de e io a es wi h he p esence o Co in he al-
loy. These alloys a o ably compa e o o he amo phous ma-
e ials conside ed as candida es o high empe a u e mag-
ne ic e ige a ion, such as Fineme - ype and
FeCoSiAlGaPCB alloys. The e ige an capaci y is in-
c eased by ⬃30% o he p esen case.
The ield dependence o he magne ic en opy change
has also been analyzed, showing a powe dependence o all
he magne ic egimes o he samples. In he e omagne ic
ange he exponen is 1. In he pa amagne ic egime, well
abo e he Cu ie empe a u e, he powe is 2, in ag eemen
wi h he Cu ie-Weiss law. Howe e , he ield dependence a
he Cu ie empe a u e de ia es om mean ield p edic ions.
ACKNOWLEDGMENTS
This wo k was suppo ed by he Spanish Go e nmen
and EU-FEDER 共P ojec No. MAT 2004-04618兲and he PAI
o Jun a de Andalucía. One o he au ho s 共J.S.B.兲is g a e ul
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FIG. 6. 共Colo online兲Tempe a u e o he ho end o he e ige a ion cycle
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