Influence of La and Ce additions on the magnetocaloric effect of Fe–B–Cr-based amorphous alloys

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 Downloaded 31 Jan 2013 o 161.111.152.13. Redis ibu ion subjec o AIP license o copy igh ; see h p://apl.aip.o g/abou / igh s_and_pe missions 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 Downloaded 31 Jan 2013 o 161.111.152.13. Redis ibu ion subjec o AIP license o copy igh ; see h p://apl.aip.o g/abou / igh s_and_pe missions 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- 6462兲, and he Uni ed S a es O ice o Na al Resea ch 共P ojec No. N00014-11-1-0311兲. 1A. M. Tishin and Y. I. Spichkin, The Magne ocalo ic E ec and i s Appli- ca ions 共Ins i u e o Physics, B is ol, 2003兲. 2K. A. Gschneidne J ., V. K. Pecha sky, and A. O. Tsokol, Rep. P og. Phys. 68, 1479 共2005兲. 3B. Yu, M. Liu, P. W. Egol , and A. Ki ano ski, In . J. Re ig. 33, 1029 共2010兲. 4V. F anco, J. S. Blazquez, C. F. Conde, and A. Conde, Appl. Phys. Le . 88, 042505 共2006兲. 5F. Johnson and R. D. Shull, J. Appl. Phys. 99, 08K909 共2006兲. 6R. Caballe o-Flo es, V. F anco, A. Conde, K. E. Knipling, and M. A. Willa d, Appl. Phys. Le . 96, 182506 共2010兲. 7V. F anco, A. Conde, and L. F. Kiss, J. Appl. Phys. 104, 033903 共2008兲. 8J. Y. Law, R. V. Ramanujan, and V. F anco, J. Alloys Compd. 508,14 共2010兲. 9V. P o enzano, A. J. Shapi o, and R. D. Shull, Na u e 共London兲429,853 共2004兲. 10J. M. D. Coey, Ra e-Ea h I on Pe manen Magne s 共Ox o d Uni e si y P ess, New Yo k, 1996兲. 11R. C. O’Handley, Mode n Magne ic Ma e ials: P inciples and Applica- ions 共Wiley, New Yo k, 2000兲. 12V. F anco, C. F. Conde, J. S. Blázquez, A. Conde, P. S ec, D. Janičko ič, and L. F. Kiss, J. Appl. Phys. 101, 093903 共2007兲. 13Y. Wang and X. Bi, Appl. Phys. Le . 95, 262501 共2009兲. 14A. Jaya aman, Valence Changes in Compounds, in Handbook on he Phys- ics and Chemis y o Ra e Ea hs, edi ed by K. A. Gschneidne J . and L. Ey ing 共No h-Holland, Ams e dam, 1979兲, Vol. 2, p. 575–611. 15J. Chappe , R. A ese-Boggiano, and J. M. D. Coey, J. Magn. Magn. Ma e . 7, 175 共1978兲. 16K. H. J. Buschow and P. G. Van Engen, J. Phys. Colloq. 41, C8-650 共1980兲. 17V. F anco and A. Conde, In . J. Re ig. 33, 465 共2010兲. 18K. Fukamichi, T. Sakakiba a, S. Todo, and Y. Sa oh, IEEE T ansl. J. Magn. Jpn. 1, 1103 共1985兲. 19N. S. Kazama, H. Fujimo i, and H. Wa anabe, Sci. Rep. Res. Ins . Tohoku Uni . A 27, 193 共1979兲. 20N. Heiman and K. Lee, AIP Con . P oc. 34, 319 共1976兲. 21K. Fukamichi, H. Koma su, T. Go o, and H. Wakabayashi, Physica B 149, 276 共1988兲. 22S. H. Aly, G. N. Nicolaides, Y. F. Tao, and G. C. Hadjipanayis, J. Phys. F: Me . Phys. 16,L21共1986兲. 23K. Fukamichi and Y. Sa oh, IEEE T ansl. J. Magn. Jpn. 1,1101共1985兲. 24P. G. De Gennes, J. Phys. Radium 23, 510 共1962兲. 25K. Yano, E. Ki a, K. Tokumi su, H. Ino, and A. Tasaki, J. Magn. Magn. Ma e . 104–107, 131 共1992兲. 26K. Yano, Y. Akiyama, K. Tokumi su, E. Ki a, and H. Ino, J. Magn. Magn. Ma e . 214, 217 共2000兲. 27V. I. Z e e , A. M. Tishin, and M. D. Kuz’min, J. Appl. Phys. 107, 043907 共2010兲. 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 Downloaded 31 Jan 2013 o 161.111.152.13. Redis ibu ion subjec o AIP license o copy igh ; see h p://apl.aip.o g/abou / igh s_and_pe missions