Soft magnetic properties of high-temperature nanocrystalline alloys: Permeability and magnetoimpedance.

So magne ic p ope ies o high- empe a u e nanoc ys alline alloys: Pe meabili y and magne oimpedance J. S. Blázquez, V. F anco, A. Conde, and L. F. Kiss Ci a ion: Jou nal o Applied Physics 93, 2172 (2003); doi: 10.1063/1.1539294 View online: h p://dx.doi.o g/10.1063/1.1539294 View Table o Con en s: h p://sci a ion.aip.o g/con en /aip/jou nal/jap/93/4? e =pd co Published by he AIP Publishing A icles you may be in e es ed in E ec o magne ic ield annealing me hods on so magne ic p ope ies o nanoc ys alline (Fe0.5Co0.5)73.5Si13.5B9Nb3Cu1 alloy J. Appl. Phys. 117, 17B729 (2015); 10.1063/1.4917324 In es iga ion on high- empe a u e magne ic pe meabili y o Si- ich nanoc ys alline (Fe0.9Co0.1)74.5Nb2Si17.5B5Cu1 alloy J. Appl. Phys. 117, 17B701 (2015); 10.1063/1.4906297 Magne ic pe meabili y o Si- ich (FeCoNi)-based nanoc ys alline alloy: The mal s abili y in a wide empe a u e ange J. Appl. Phys. 113, 17A310 (2013); 10.1063/1.4794718 E ec o P addi ion on nanoc ys alliza ion and high empe a u e magne ic p ope ies o low B and Nb con aining FeCo nanocomposi es J. Appl. Phys. 111, 07A301 (2012); 10.1063/1.3670056 High- empe a u e gian magne oimpedance in Fe-based nanoc ys alline alloy J. Appl. Phys. 87, 5263 (2000); 10.1063/1.373315 [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: 150.214.182.17 On: Wed, 27 Jan 2016 09:39:13 So magne ic p ope ies o high- empe a u e nanoc ys alline alloys: Pe meabili y and magne oimpedance J. S. Bla ´zquez, V. F anco, and A. Condea) Depa amen o de Fı ´sica de la Ma e ia Condensada, ICMSE-CSIC, Uni e sidad de Se illa, P. O. Box 1065, 41080 Se illa, Spain L. F. Kiss Resea ch Ins i u e o Solid S a e Physics and Op ics, Hunga ian Academy o Sciences, P. O. Box 49, 1525 Budapes , Hunga y 共Recei ed 5 June 2002; accep ed 21 No embe 2002兲 The echnological applicabili y o FeCoNbBCu alloys is sugges ed in e ms o measu emen s o oom empe a u e magne oimpedance and empe a u e dependence o magne ic pe meabili y ␮ . Resul s o he Fe78-xCoxNb6B15Cu1alloy se ies show ha oom empe a u e so magne ic p ope ies a e enhanced in he lowes Co con aining alloy ( ␮ ⬃10 500 and magne oimpedance a io ⬃60% a 1 MHz兲. Howe e , pe meabili y exhibi s a smoo he he mal dependence in he alloys wi h medium and high Co con en . A adeo be ween magne ic so ness and i s he mal s abili y e eals he alloy wi h 39 a . % Co as he mos sui able composi ion among hose s udied, cha ac e ized by a empe a u e coe icien o ⬃0.02%/K om oom empe a u e up o 900 K. This alue is 1 o de o magni ude smalle han hose obse ed o FeSiBCuNb 共FINEMET- ype兲alloys and Mn e i es and ex ended o e a much wide empe a u e ange han in hese ma e ials. © 2003 Ame ican Ins i u e o Physics. 关DOI: 10.1063/1.1539294兴 I. INTRODUCTION So magne ic nanoc ys alline alloys ha e been p o usely s udied since he de elopmen o FINEMET 共FeSiBNbCu兲1 and NANOPERM alloys 共FeMB and FeMBCu, M⫽Nb, Z , H ...兲.2These ma e ials p esen a wo-phase mic os uc u e, in which e omagne ic nanoc ys als 共 ␣ -FeSi o ␣ -Fe, espec- i ely兲a e embedded in a esidual e omagne ic amo phous phase. Thei ou s anding so -magne ic p ope ies a oom empe a u e a e widely co e ed in he li e a u e.3Howe e , as he empe a u e inc eases, so magne ic p ope ies a e los due o he ansi ion o he amo phous phase o he pa amag- ne ic s a e,4which limi s he applicabili y o hese ma e ials a high empe a u es. Sea ching o so magne ic nanoc ys- alline alloys wi h high empe a u e applicabili y led o he de elopmen o HITPERM- ype alloys 共FeCoMBCu兲,5in which pa ial subs i u ion o Fe by Co was shown o enhance he Cu ie empe a u e o he amo phous phase. The highe coe ci i y exhibi ed by HITPERM alloys, compa ed o FINEMET and NANOPERM, has been ex- plained in e ms o he di e en e olu ion o he sa u a ion magne os ic ion cons an ␭Sdu ing nanoc ys alliza ion. Whe eas in FINEMET and NANOPERM alloys he con i- bu ions o ␭Scoming om he c ys alline and esidual amo - phous phases a e o di e en sign, gi ing an o e all alue close o ze o, in HITPERM alloys bo h con ibu ions a e posi i e.3In his case, he so ness o he ma e ial is con- olled by he ela i e a ia ion o he magne os ic ion om he amo phous phase o he c ys alline one.6 The e ha e been nume ous s udies conce ning he mi- c os uc u al cha ac e iza ion and magne ic phase ansi ion in HITPERM- ype alloys.3,5,7–10 Howe e , he e a e s ill ew esul s on magne ic p ope ies ele an o possible applica- ions o hese ma e ials, such as magne ic pe meabili y ␮ and gian magne oimpedance e ec 共GMI兲. The la e has been a ield o in ensi e esea ch in ecen yea s;11–13 o da e i is a new way o he applica ion o so magne ic ma e ials.14–17 The e a e nume ous s udies o he di e en ac o s a ec ing he magne oimpedance beha io o so magne ic nanoc ys alline alloys as FINEMET and NANOP- ERM, analyzing, o example, he in luence o he he mal ea men s,18–25 composi ional e ec s,18–20 he in luence o domain s uc u e and induced aniso opies,21–23 he e ec o he measu ing equency,19–22,24 and empe a u e,24,25 e c. Howe e , he e is a lack o da a in he li e a u e conce ning he HITPERM amily o alloys. In his wo k he in luence o he Co o Fe a io on he oom empe a u e magne oimpedance and he mal depen- dence o magne ic pe meabili y o HITPERM- ype alloys has been s udied. I will be shown ha al hough Co addi ion de e io a es he oom empe a u e so magne ic p ope ies o he alloy, a wide empe a u e ange o s able magne ic p op- e ies is ob ained. II. EXPERIMENT Amo phous ibbons, ⬃20 ␮ m hick and ⬃5 mm wide, o nominal composi ions Fe78⫺xCoxNb6B15Cu1共x⫽18, 39, 60兲we e p oduced a Wa saw Uni e si y o Technology by he single olle mel -spinning echnique. The de i i ica ion a兲Au ho o whom co espondence should be add essed; elec onic mail: [email p o ec ed] JOURNAL OF APPLIED PHYSICS VOLUME 93, NUMBER 4 15 FEBRUARY 2003 21720021-8979/2003/93(4)/2172/6/$20.00 © 2003 Ame ican Ins i u e o Physics [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: 150.214.182.17 On: Wed, 27 Jan 2016 09:39:13 p ocess o he alloys has been s udied by di e en ial scan- ning calo ime y 共DSC兲, ansmission elec on mic oscopy and x- ay di ac ion echniques. Pe meabili y measu emen s we e pe o med on o oidal samples a a equency o 6 kHz and an applied ield low enough o assu e he measu emen o ini ial pe meabili y 共⬃ 0.5 A/m兲. The expe imen consis ed o se e al hea ing– cooling cycles and bo h he measu emen and hea ea men o he samples we e pe o med a he same ime. Fo hese measu emen s wo coils we e wounded a ound he sample. Wi h he i s coil an ac ield is applied o he sample, whe eas he signal induced in he second coil is de ec ed using a lock-in echnique. An impedance analyze 共Hewle - Packa d 4192A兲was used o calib a e he alues o pe me- abili y a oom empe a u e. Fo magne oimpedance measu emen s he impedance analyze was used. Two elec ical con ac s we e spo welded o he samples a a dis ance o 5 cm. DSC expe imen s con- i med ha his p ocedu e did no a ec he de i i ica ion p ocess o he alloys s udied. Samples we e annealed in a halogen-lamp u nace in acuum a di e en s ages o he de i i ica ion p ocess p esen ed in Table I. Fo measu ing he ield dependence o he impedance, an ac in ensi y o 10 mA a equencies anging om 0.5 o 5 MHz was applied h ough he sample. The maximum applied ield was 7.2 kA/m. III. RESULTS A. De i i ica ion p ocess The de i i ica ion p ocess o he as-cas samples occu s in wo main s ages.26 Du ing he i s one, a nanoc ys alline mic os uc u e is o med, in which ␣ -FeCo nanoc ys als wi h an a e age g ain size o ⬃5 nm a e embedded in a esidual amo phous ma ix. The c ys alline olume ac ion a he end o he nanoc ys alliza ion p ocess is ⬃55% o he alloys wi h 18 and 39 a . % Co, bu i is lowe in he alloy wi h 60 a . % Co 共⬃ 45%兲.26 A highe empe a u es 共⬎900 K兲, ec ys alliza ion o a ac ion o he ␣ -FeCo c ys alli es and he esidual amo phous ma ix p oduces a ully c ys alline alloy, wi h he appea ance o bo ide phases, mainly 共FeCo兲 共FeCo兲23B6.27 B. Ini ial pe meabili y Figu e 1共a兲shows he e olu ion o he ini ial pe meabil- i y wi h empe a u e o Fe60Co18Nb6B15Cu1as-cas sample submi ed o con inuous hea ing and cooling cycles. The cha ac e is ic ea u es ha e been numbe ed in he igu e. Ini- ially 共1兲 he elaxa ion o he in e nal s esses p o okes a p og essi e inc ease o he oom empe a u e pe meabili y; cooling cycles 共2兲show ha pe meabili y emains cons an o empe a u es lowe han 550 K a his s age. A cha ac e - is ic Hopkinson peak is obse ed a he Cu ie empe a u e o he amo phous phase, which is due o a as e dec ease o magne ic aniso opy han ha o magne iza ion wi h inc eas- ing empe a u e, and hus he pe meabili y di e ges a he Cu ie poin .28 Abo e he Cu ie poin o he amo phous phase, an ab up all in he pe meabili y is obse ed 共3兲, due o he ansi ion o he sys em o he pa amagne ic s a e. A highe empe a u es, an inc ease o pe meabili y a he onse o nanoc ys alliza ion occu s 共4兲, which is connec ed wi h he appea ance o he e omagne ic nanoc ys als o he ␣ -FeCo phase.29 When his mic os uc u e is achie ed, he sys em shows he highes oom empe a u e pe meabili y. Howe e , no Hopkinson peak can be de ec ed a he Cu ie poin o he esidual amo phous phase (TC am), which can be due o he non-ze o alue o he e ec i e magne ic aniso - opy o he whole sys em: he nanoc ys als p esen a much highe Cu ie empe a u e han he amo phous ma ix and he e o e, ␮ does no di e ge a TC am . Also, he all in ␮ a TC am is smoo he o he nanoc ys allized sample han o he ully amo phous one. In ac , he esidual amo phous ma ix is no homogeneous30 and hus he Cu ie empe a u e is no well de ined.31 Fo his alloy, oom empe a u e pe meabili y shows high alues a his s age, bu i depends s ongly on empe a u e, which is a nondesi able e ec o high empe a- FIG. 1. Ini ial pe meabili y s empe a u e in successi e hea ing–cooling cycles o : 共a兲Fe60Co18Nb6B15Cu1and 共b兲Fe39Co39Nb6B15Cu1alloys. Numbe s indica e he sequence o hea ing-cooling cycles. TABLE I. The mal ea men s o samples submi ed o magne oimpedance expe imen s. Ini ial nanoc ys alline co esponds o samples wi h low c ys- alline olume ac ion, while inal nanoc ys alline co esponds o samples annealed up o he end o he i s c ys alliza ion s age. Alloy Sample Hea ea men Fe60Co18 Nb6B15 Cu1 S uc u ally elaxed 15 min a 600 K Ini ial nanoc ys alline 15 min a 725 K Final nanoc ys alline 15 min a 800 K Fe39Co39 Nb6B15 Cu1 S uc u ally elaxed 15 min a 600 K Ini ial nanoc ys alline 15 min a 725 K Final nanoc ys alline 15 min a 850 K S uc u ally elaxed 15 min a 600 K Fe18Co60 Nb6B15 Cu1Ini ial nanoc ys alline 15 min a 700 K Final nanoc ys alline 15 min a 800 K 2173J. Appl. Phys., Vol. 93, No. 4, 15 Feb ua y 2003 Blazquez e al. [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: 150.214.182.17 On: Wed, 27 Jan 2016 09:39:13 u e applica ions o he ma e ial. As nanoc ys alliza ion p og esses, pe meabili y inc eases 共5兲, bu o empe a u es abo e he second ans o ma ion s age pe meabili y de- c eases 共6兲, and he so magne ic p ope ies o he ma e ial a e los in all he explo ed empe a u e ange 共7兲due o he p esence o bo ide- ype phases. The sligh inc ease in ␮ as empe a u e dec eases can be explained in e ms o he Cu ie empe a u es o he bo ide- ype phases o med, especially he 共FeCo兲23B6phase, wi h TC⫽784 K.32 The beha io o he o he alloys s udied shows simila ends, howe e a wide empe a u e ange o cons an pe - meabili y can be obse ed o he nanoc ys alline samples o he alloys wi h highe Co con en 关Fig. 1共b兲兴: In con as wi h he 18 a . % Co alloy, whe e ␮ dec eases a empe a u es abo e 500 K, he alloys wi h 39% and 60% ha e a cons an alue o pe meabili y up o 950 and 900 K, espec i ely. This can be asc ibed o he highe Cu ie empe a u e o he amo - phous ma ix, which migh allow he magne ic coupling be- ween he nanoc ys als h ough he ma ix up o highe empe a u es.4 C. Magne oimpedance Figu e 2 shows he modulus o impedance 共兩Z兩兲 e sus dc applied magne ic ield 共H兲, ob ained a oom empe a u e a a equency o 1 MHz, o samples o he 18 a . % Co alloy in he as-quenched s a e and a e annealing. The alue o 兩Z兩a he maximum applied ield dec eases as he c ys alline ac- ion inc eases, being he same o as-cas and elaxed samples, in ag eemen wi h he educ ion o dc esis i i y wi h he p og ess o c ys alliza ion. Usually he GMI e ec is desc ibed in e ms o he mag- ne oimpedance a io 共MIR 兲, calcula ed as: MIR ⫽100• 兩 Z共H兲 兩 ⫺ 兩 Z共Hmax兲 兩 兩 Z共Hmax兲 兩 , whe e 兩 Z(Hmax) 兩 is he impedance modulus measu ed a maximum applied ield 共7200 A/m兲. Figu e 3 shows MIR alues e sus H, o all he s udied alloys in he as-cas , s uc u ally elaxed, ini ial-nanoc ys alline and inal- nanoc ys alline s a es. The maximum alue o MIR e sus annealing empe a u e is ep esen ed in Fig. 4. Fo he alloy wi h 18 a . % Co he GMI e ec inc eases o he elaxed sample wi h espec o he as-cas sample, eaches a maxi- mum alue o he ini ial-nanoc ys alline sample 共⬃ 60%兲 and dec eases o he inal-nanoc ys alline sample. Howe e , o he highe Co con en alloys, he maximum GMI e ec appea s o he as-cas samples, dec easing as he annealing empe a u e inc eases. The magne oimpedance scans 共Fig. 3兲show a single- peak s uc u e o all he as-cas samples s udied and o he ini ial-nanoc ys alline sample o he 18 a . % Co alloy; how- e e a double peak s uc u e can be obse ed o all he o he FIG. 2. Magne oimpedance modulus o Fe60Co18Nb6B15Cu1alloy: 共a兲as- cas , 共b兲s uc u ally elaxed, 共c兲ini ial-nanoc ys alline, and 共d兲 inal- nanoc ys alline samples. FIG. 3. Magne oimpedance a io o he di e en alloys s udied: 共a兲as-cas , 共b兲s uc u ally- elaxed, 共c兲ini ial-nanoc ys alline, and 共d兲 inal- nanoc ys alline samples FIG. 4. In luence o he mic os uc u e on he maximum magne oimpedance a io. 2174 J. Appl. Phys., Vol. 93, No. 4, 15 Feb ua y 2003 Blazquez e al. [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: 150.214.182.17 On: Wed, 27 Jan 2016 09:39:13 samples s udied. This kind o wo-peak s uc u e and he hys e e ic beha io o magne oimpedance a e dele e ious o he applicabili y o he alloys. IV. DISCUSSION The beha io o he pe meabili y and magne oimpedance is co ela ed wi h he p e iously epo ed beha io o coe - ci i y and magne os ic ion.6,26 As he ac o s ha a ec he magne ic p ope ies depend s ongly on he mic os uc u e, i is sui able o di ide he samples s udied in amo phous samples 共as-cas and s uc u ally elaxed samples兲and nano- c ys alline samples 共annealed a he beginning and a he end o he nanoc ys alliza ion兲. A. Amo phous samples Figu e 5 shows he ini ial pe meabili y measu ed a 400 K共maximum empe a u e below which ␮ emains app oxi- ma ely cons an o all he alloys s udied and no p oducing u he s uc u al ans o ma ion o he samples兲 e sus maximum achie ed empe a u e in he p e ious hea ea - men o he con inuous hea ing-cooling cycle expe imen s. In his igu e i is possible o obse e he e olu ion o ␮ wi h he mic os uc u e. An inc ease in pe meabili y wi h he s uc u al elaxa ion phenomena can be ound o all he s udied alloys, being he e ec la ge as he Co con en de- c eases in he alloy. This e olu ion di e s om he one e- po ed o coe ci i y26 and om he obse ed e olu ion in MIR 共Fig. 4兲. In ac , only o he 18 a . % Co alloy is a clea so ening o he magne ic p ope ies obse ed a e s uc u al elaxa ion, e lec ed in he magne oimpedance esul s as an inc ease in he GMI e ec in s uc u ally elaxed samples. This di e ence can be unde s ood in e ms o he p e i- ously p oposed mechanism o he inc ease in oom empe a- u e coe ci i y: he domain wall s abiliza ion phenomena.6 Pe meabili y measu emen s and hea ea men s o he samples we e made simul aneously, hus he annealing was unde he p esence o an ac ield. I has been epo ed ha annealing unde ac ield diminishes 共o e en nulls兲 he do- main wall s abiliza ion e ec ,33 which can explain he di e - en e olu ion o he pe meabili y and he coe ci i y wi h he s uc u al elaxa ion. As i has been poin ed be o e, he beha io o MIR wi h he s uc u al elaxa ion ag ees wi h he beha io ound o he coe ci i y.6,26 Howe e , he domain wall s abiliza ion phenomena would be a sui able explana ion o he magne ic ha dening o he highe Co con en alloys only i i is pos- sible o con i m ha he domain wall mo ion is a con ibu ing mechanism o he magne iza ion p ocess a he equency used in he magne oimpedance expe imen s 共1 MHz兲. The equency e olu ion o MIR in nanoc ys alline alloys shows ha he maximum alue o MIR inc eases up o a ce ain alue o equency, a e which i dec eases. This all in he GMI e ec has been associa ed wi h he disappea ance o he con ibu ion o he domain wall mo ion o he magne iza ion p ocess a high equencies.15,34 The e o e, he measu ing equency was changed om 0.5 o 5 MHz in he magne- oimpedance expe imen s. A con inuous inc ease in MIR was obse ed as he applied equency is inc eased, con i ming ha he domain wall mo ion is a con ibu ing mechanism o he magne iza ion p ocess a 1 MHz and, he e o e, he do- main wall s abiliza ion is a sui able explana ion o he mag- ne ic ha dening o he high Co con en alloys. The wo-peak s uc u e obse ed in he magne oimped- ance scans is ela ed o he magne ic aniso opy ield, HK, being equal o he obse ed shi o he maximum alue o MIR wi h espec o H⫽0.34 In ou case, his is ue o he 18 a . % Co con aining alloy, howe e , because he domain wall s abiliza ion phenomena a ec he posi ion o he maxi- mum alue o MIR,35 i is no possible o a i m he same o he 39 and 60 a . % Co alloys. In amo phous samples, he main con ibu ion o he an- iso opy ield is he magne oelas ic aniso opy, and HKcan be exp essed as HK⫽2K ␮ 0MS ⫽3␭S ␴ ␮ 0MS, whe e K⫽共3/2兲␭S ␴ , is he magne oelas ic aniso opy con- s an , ␭S he sa u a ion magne os ic ion cons an , ␴ he in- e nal s esses, ␮ 0 he acuum pe meabili y, and MS he sa u- a ion magne iza ion. Fo he s uc u ally elaxed sample o he 18 a . % Co alloy HK, ob ained om he posi ion o maximum alue o MIR, is ⬃200 A/m. The alues o ␭Sand ␮ 0MS o his sample a e 30 ppm and 1.1 T, espec i ely, which gi es a alue o ⬃1 MPa o he in e nal s esses and an aniso opy cons an alue compa able o hose ound in o he me allic glasses wi h simila sa u a ion magne os ic- ion cons an s.36 B. Nanoc ys alline samples Bo h he pe meabili y and magne oimpedance esul s ag ee wi h he epo ed beha io o coe ci i y a e he nanoc ys alliza ion p ocess,26 in which he coe ci i y de- c eases a he beginning o he nanoc ys alliza ion only o he alloy wi h 18 a . % Co. Fo his alloy, he ini ial pe me- abili y shows high alues a low empe a u es 共⬍500 K兲in nanoc ys allized samples 共⬃ 10 500兲bu low alues can be ound in he o he alloys 共⬃ 1000兲. The e y low alues ob ained o samples annealed a e he second ans o ma- FIG. 5. Ini ial pe meabili y measu ed a 400 K s maximum eached em- pe a u e in he p e ious ea men . A ows indica e he c ys alliza ion p o- cesses de ec ed by DSC. 2175J. Appl. Phys., Vol. 93, No. 4, 15 Feb ua y 2003 Blazquez e al. [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: 150.214.182.17 On: Wed, 27 Jan 2016 09:39:13 ion s ages a e due o he o ma ion o bo ide- ype phases which d as ically ha den he magne ic p ope ies. Fo o he HITPERM- ype composi ion, Fe44Co447 B4Cu1,8 he maximum ini ial pe meabili y measu ed a oom empe a u e was 1800, ob ained a 0.4 kHz. A 6 kHz 共mea- su ing equency in ou expe imen s兲 he alue o ␮ is ⬃1000, simila o he ob ained alue o ou nanoc ys allized alloy Fe39 Co39Nb6B15Cu1, bu 1 o de o magni ude lowe han he maximum alue exhibi ed by he nanoc ys alline samples o Fe60 Co18Nb6B15Cu1共⬃10 500兲. The e olu ion o pe meabili y and he dec ease o esis- i i y wi h nanoc ys alliza ion mus a ec he e olu ion o he GMI e ec .37 Fo samples o he di e en alloys a he same annealing s age 共s uc u ally elaxed, ini ial nanoc ys- alline and inal nanoc ys alline兲, he 兩Z兩 alues a he maxi- mum applied ield a e simila , indica ing ha esis i i y does no di e conside ably be ween hese samples. The e o e, he composi ional e ec on GMI o he se ies s udied migh be asc ibed o he di e en alues o pe meabili y. The GMI e ec inc eases a he beginning o he nanoc- ys alliza ion only o he alloy wi h 18 a . % Co, as i has been p e iously obse ed o FINEMET and NANOPERM composi ions.37 Fo hese alloys, bo h he enhancemen o magne ic so ness and he dec ease o esis i i y con ibu e o he inc ease in he GMI e ec . Howe e , o he 39 and 60 a . % Co alloys he GMI e ec is lowe in he nanoc ys al- lized samples han in he amo phous samples, despi e he dec ease o he esis i i y bu in ag eemen wi h he obse ed beha io o he ini ial pe meabili y and he epo ed e olu- ion o he coe ci i y.26 This kind o co ela ion be ween he e olu ion o esis i i y and GMI e ec has also been ob- se ed o o he nanoc ys alline alloys, whe e a dec ease o esis i i y a ad anced s ages o nanoc ys alliza ion canno a oid he dec ease o he GMI e ec .37 The di e en e olu ion o he magne os ic ion cons an o he di e en alloys can explain he di e en obse ed be- ha io . In ac , he nanoc ys alline ␣ -FeCo phase ha ap- pea s in he 39 and 60 a . % Co alloys wi h composi ions close o Fe61 Co39 and Fe40 Co60 , espec i ely,38 shows a highe ␭S alue 共⬃65 ppm兲39 han ha co esponding o he amo phous alloy 共⬃10–15 ppm兲6and his makes he ne magne os ic ion cons an inc ease as he nanoc ys alliza ion p og esses. Howe e , o he alloy wi h 18 a . % Co, he magne os ic ion cons an is ⬃15 ppm o bo h he amo phous6and ␣ -Fe82Co18 c ys alline phases.39 Fo FINEMET and NANOPERM alloys, ␭Sis nega i e in he nanoc ys als and posi i e in he amo phous phase, p oducing a dec ease o he ne magne os ic ion o he sys em and, consequen ly, an enhancemen o he magne ic p ope ies a oom empe a u e.3 An impo an ea u e o possible applica ions o hese ma e ials is he empe a u e ange o cons an pe meabili y. S udies on he empe a u e dependence o he ini ial pe me- abili y in nanoc ys allized FINEMET- ype alloys40 show ha ␮ ab up ly dec eases a empe a u es highe han 575 K. To cha ac e ize quan i a i ely he empe a u e s abili y o ␮ , he empe a u e coe icien o pe meabili y can be used as a pa ame e o compa ison. Whe eas in FINEMET alloys pe - meabili y dec eases a a a e o ⬃0.3%/K in a empe a u e ange om 400 o 500 K,40 in he Fe39 Co39Nb6B15Cu1alloy he empe a u e coe icien is ⬃0.02%/K in a empe a u e ange om 400 o 900 K, indica ing an imp o emen in he high empe a u e applica ions o his alloy wi h espec o FINEMET. This pa ame e is e y impo an o some ech- nological applica ions as LC il e s, whe e e i es a e usually used. A ypical alue o he empe a u e coe icien o pe - meabili y in Mn e i es is ⬃0.3%/K bu hey a e limi ed o low empe a u e applica ions due o hei low Cu ie empe a- u es 共⬃450 K兲. V. CONCLUSIONS Two cha ac e is ic p ope ies ha a e in e es ing o so magne ic applica ions o HITPERM- ype alloys ha e been s udied: pe meabili y and magne oimpedance. The beha io is in line wi h p e ious esul s on coe ci i y, and can be explained in e ms o domain wall s abiliza ion phenomenon, he di e ence be ween he magne os ic ion cons an o he cons i u ing wo phases and g ain coa sening. The oom em- pe a u e so ness is enhanced in he alloy wi h he lowes Co con en which exhibi s ␮ ⬃10 500 and a maximum alue o MIR⬃60% 共a 1 MHz兲 o nanoc ys alline samples wi h low c ys alline olume ac ion. Al hough he ob ained alues o he o he composi ions 共39 and 60 a . % Co兲a e ␮ ⬃1000 and a maximum alue o MIR⬍10% 共a 1 MHz兲, high em- pe a u e applicabili y is clea ly enhanced in hese alloys, showing a wide empe a u e ange wi h app oxima ely con- s an pe meabili y. This sui abili y o high empe a u e ap- plica ions can be exp essed h ough he empe a u e coe i- cien o he pe meabili y 共⬃0.02%/K om oom empe a u e up o 900 K o he alloy wi h 39 a . % Co兲, 1 o de o magni ude lowe han hose ound in FINEMET and Mn e - i es and ex ended o e a much wide empe a u e ange han in hese ma e ials. 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