The influence of Co addition on the magnetocaloric effect of Nanoperm-type amorphous alloys

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 View Table o Con en s: h p://sci a ion.aip.o g/con en /aip/jou nal/jap/100/6? e =pd co Published by he AIP Publishing A icles you may be in e es ed in The e ec o dis ibu ed exchange pa ame e s on magne ocalo ic e ige a ion capaci y in amo phous and nanocomposi e ma e ials J. Appl. Phys. 111, 07A334 (2012); 10.1063/1.3679456 In luence o Co and Ni addi ion on he magne ocalo ic e ec in Fe 88 − 2 x Co x Ni x Z 7 B 4 Cu 1 so magne ic amo phous alloys Appl. Phys. Le . 96, 182506 (2010); 10.1063/1.3427439 Magne ocalo ic e ec in Fe–Z –B–M ( M = Mn , C , and Co) amo phous sys ems J. Appl. Phys. 105, 07A910 (2009); 10.1063/1.3054369 In luence o Ge addi ion on he magne ocalo ic e ec o a Co-con aining Nanope m- ype alloy J. Appl. Phys. 103, 07B316 (2008); 10.1063/1.2835688 The magne ocalo ic e ec in so magne ic amo phous alloys J. Appl. Phys. 101, 09C503 (2007); 10.1063/1.2709409 [This a icle is copy igh ed as indica ed in he a icle. Reuse o AIP con en is subjec o he e ms a : h p://sci a ion.aip.o g/ e mscondi ions. Downloaded o ] IP: 150.214.182.116 On: F i, 22 Jan 2016 15:32:26 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 [This a icle is copy igh ed as indica ed in he a icle. Reuse o AIP con en is subjec o he e ms a : h p://sci a ion.aip.o g/ e mscondi ions. Downloaded o ] IP: 150.214.182.116 On: F i, 22 Jan 2016 15:32:26 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 [This a icle is copy igh ed as indica ed in he a icle. Reuse o AIP con en is subjec o he e ms a : h p://sci a ion.aip.o g/ e mscondi ions. Downloaded o ] IP: 150.214.182.116 On: F i, 22 Jan 2016 15:32:26 ⌬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 [This a icle is copy igh ed as indica ed in he a icle. Reuse o AIP con en is subjec o he e ms a : h p://sci a ion.aip.o g/ e mscondi ions. Downloaded o ] IP: 150.214.182.116 On: F i, 22 Jan 2016 15:32:26 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 o Jun a de Andalucía o a esea ch con ac . 1E. Wa bu g, Ann. Phys. Chem. 13,141共1881兲. 2W. F. Giauque and G. P. MacDougall, Phys. Re . 43,768共1933兲. 3G. V. B own, J. Appl. Phys. 47, 3673 共1976兲. 4C. A. Zimm, A. Jas ab, A. S e nbe g, V. K. Pecha sky, K. A. Gschneidne , J ., M. G. Osbo ne, and I. E. Ande son, Ad . C yog. Eng. 43,1759共1998兲. 5A. M. 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Phys. 100, 064307 共2006兲 [This a icle is copy igh ed as indica ed in he a icle. Reuse o AIP con en is subjec o he e ms a : h p://sci a ion.aip.o g/ e mscondi ions. Downloaded o ] IP: 150.214.182.116 On: F i, 22 Jan 2016 15:32:26