Enhancement of soft magnetic properties in the selected group of amorphous alloys was examined by different
experimental methods. It was shown that permeability for annealed samples (at Ta for 1 h; 300 K < Ta < 900 K)
plotted vs. Ta shows a maximum at which is 700, 725, 725, and 750 K for Fe82Nb2B14Y2, Fe82Nb2B14Gd2,
Fe82Nb2B14Tb2 and Fe82Nb2B14Dy2 alloy, respectively. For samples after the optimization annealing permeability
is at least 10 times higher than in the as-quenched state. The optimized microstructure is free of iron nanograins
and corresponds to so-called relaxed amorphous phase

Chrobak, Artur

Haneczok, Grzegorz

Hendrych, A.

Kansy, Jerzy

Kotur, B.

Zivotsky, O.

Acta Physica Polonica A

A. Chrobak

G. Haneczok

O. Zivotsky

A. Hendrych

J. Kansy

B. Kotur

Crossref

Optimization of Soft Magnetic Properties in Fe82Nb2B14RE2 (RE = Y, Gd, Tb and Dy) Group of Amorphous Alloys

Enhancement of soft magnetic properties in the selected group of amorphous alloys was examined by different experimental methods. It was shown that permeability for annealed samples (at T-a for 1 h; 300 K < T-a < 900 K) plotted vs. T-a shows a maximum at which is 700, 725, 725, and 750 K for Fe82Nb2B14Y2, Fe82Nb2B14Gd2, Fe82Nb2B14Tb2 and Fe82Nb2B14Dy2 alloy, respectively. For samples after the optimization annealing permeability is at least 10 times higher than in the as-quenched state. The optimized microstructure is free of iron nanograins and corresponds to so-called relaxed amorphous phase.Web of Science130491991

Životský, Ondřej

Hendrych, Aleš

Kotur, Bogdan

DSpace at VSB Technical University of Ostrava

Vol. 130 (2016) ACTA PHYSICA POLONICA A No. 4Proceedings of the XXIII Conference on Applied Crystallography, Krynica Zdrój, Poland, September 20–24, 2015Optimization of Soft Magnetic Properties in Fe82Nb2B14RE2(RE = Y, Gd, Tb and Dy) Group of Amorphous AlloysA. Chrobaka,∗, G. Haneczokb, O. Zivotskyc, A. Hendrychc, J. Kansyb and B. KoturdaUniversity of Silesia, Institute of Physics, Uniwersytecka 4, 40-007 Katowice, PolandbUniversity of Silesia, Institute of Materials Science (SMCEBI), 75 Pułku Piechoty 1, 41-500 Chorzów, PolandcVŠB-Technical University of Ostrava, Institute of Physics, 17. listopadu 15, 708 33 Ostrava-Poruba, Czech RepublicdIvan Franko National University of Lviv, Kyryla and Mefodia St. 6, 79005 Lviv, UkraineEnhancement of soft magnetic properties in the selected group of amorphous alloys was examined by differentexperimental methods. It was shown that permeability for annealed samples (at Ta for 1 h; 300 K < Ta < 900 K)plotted vs. Ta shows a maximum at which is 700, 725, 725, and 750 K for Fe82Nb2B14Y2, Fe82Nb2B14Gd2,Fe82Nb2B14Tb2 and Fe82Nb2B14Dy2 alloy, respectively. For samples after the optimization annealing permeabilityis at least 10 times higher than in the as-quenched state. The optimized microstructure is free of iron nanograinsand corresponds to so-called relaxed amorphous phase.DOI: 10.12693/APhysPolA.130.916PACS/topics: 81.07.Bc, 75.50.Tt, 75.60.–d, 76.80.+y1. IntroductionIt is well known that soft magnetic properties of ironbased amorphous alloys can be enhanced by applying aspecific annealing at temperatures close to crystalliza-tion temperature. After such annealing a low field mag-netic permeability can increase even 20 times and a co-ercive field can go down below 1 A/m [1–8]. The ob-served effects are explained by formation of an optimizedmicrostructure which in general can be of two types:(i) iron nanograins embedded into a residual amorphousphase [1–5] or (ii) the so-called relaxed amorphous phasefree of iron nanograins for which free volume and internalstresses are significantly reduced [2, 6–8]. The type of theoptimized microstructure strongly depends on alloyingadditions and parameters of the applied annealing. In-fluence of RE (rare earth) additions with a high localizedmagnetic moment on magnetic properties and crystal-lization of the same group of amorphous alloys in the as-quenched state have been already reported in [9] and [10],respectively. It was shown for example that 2 at.% of REaddition leads to an increase of the Curie temperature byno more than 34 K (for Fe82Nb2B14Gd2) in relation tothe reference Fe82Nb2B14Y2 alloy (TC = 416 K) [9]. Astrong spin–orbit coupling of Tb and Dy atoms leads toan additional magnetic anisotropy of the examined al-loys and to a magnetic hardening (permeability dropsdown about 5 times and a finger-print domain struc-ture appears) [10]. Moreover, a localized magnetic mo-ment of RE atoms cause an increase of the activationenthalpy of crystallization by about 0.8 eV (4.4 eV forthe Fe82Nb2B14Y2 and 5.2 eV for the Fe82Nb2B14Tb2alloy) [10].∗corresponding author; e-mail: artur.chrobak@us.edu.plThe aim of the present paper is to study the optimiza-tion of soft magnetic properties in the family of amor-phous alloys of type Fe82Nb2B14RE2 (RE = Y, Gd, Tband Dy). The key point is to examine an influence ofdifferent thermal annealing on magnetic properties andformation of the so-called relaxed amorphous phase. TheFe82Nb2B14Y2 alloy with non-magnetic yttrium is takenas a reference alloy because Y has similar to RE atomicradius.2. Experimental procedure and resultsThe examined amorphous alloys were prepared by ap-plying a melt spinning technique in a helium atmosphere.The melt was prepared from pure binary REFe2 (RE=Y,Gd, Tb, and Dy) and NbFe2 compounds. The purity ofthe initial metals were : Fe (99.99 wt%), Y (99.96 wt%),Gd (99.96 wt%), Tb (99.96 wt%), and Dy (99.96 wt%).Rare earth metals in a form of binary compounds REFe2and NbFe2 were primarily obtained by the arc-meltingtechnique from metals of the same purity. The obtainedalloys were in the form of strips with thickness and widthof 20–25 µm and 3 mm, respectively. The melt spunribbons in the as-quenched state were annealed at tem-peratures Ta (300 K < Ta < 900 K) for 1 h, and forannealed samples the following measurements were car-ried out: (i) low field magnetic permeability (Agilentmeter E4980a, field 0.5 A/m), (ii) magnetization ver-sus temperature (Faraday type magnetic balance, field0.5 T, 300 K < T < 1100 K, heating rate 5 K/min) and(iii) Mössbauer spectra (standard transmission geometrywith constant acceleration drive). Moreover, for selectedsamples, magnetic domain structure was examined us-ing Zeiss optical microscope adopted for magneto-opticalKerr microscopy.Figure 1 shows the low field magnetic permeabilityµ measured at room temperature for annealed samples(916)Optimization of Soft Magnetic Properties. . . 917Fig. 1. Low field magnetic permeability measured atroom temperature versus 1 h annealing temperature Ta.Fig. 2. Normalized magnetization versus temperaturefor sample preliminary annealed at different temper-atures for (a) Fe82Nb2B14Y2, (b) Fe82Nb2B14Tb2,(c) Fe82Nb2B14Gd2, and (d) Fe82Nb2B14Dy2.plotted versus Ta (for the as-quenched state Ta = 300 K).One can see that in all examined cases µ(Ta) curve showsa distinct maximum indicating that 1 h annealing at awell-defined temperature (denoted as Top) causes a signif-icant enhancement of the magnetic permeability. In fact,according to Fig. 1, annealing at Top results in more thana tenfold increase of µ.Figure 2 shows magnetization in saturation versus tem-perature determined for samples of different alloys inthe as quenched states, after preliminary annealing atTop (the optimization annealing) and after preliminaryannealing at Ta > Top. One can see that for samples inthe as quenched states magnetization drops down withtemperature and at T > 450 K the examined alloysare in paramagnetic state. In temperature range 800 ≤T ≤ 900 Kmagnetization in saturation strongly increasesdue to formation of iron nanograins which was confirmedby X-ray examinations and high resolution transmissionelectron microscopy observations [3]. At temperaturesT > 900 Kmagnetization goes down up to the Curie tem-perature of the already formed crystalline phase. Similarcurves were obtained for samples preliminary annealedfor 1 h at Top i.e. after the 1 h optimization annealing.In contrast, magnetization versus temperature for sam-ples preliminary annealed at temperature Ta = 850 K(i.e. at Ta  Top) do not show an intermediate para-magnetic state. This is obviously due to formation ofiron grains (nanograins) during the preliminary anneal-ing. In each examined case a residual amorphous phasewith the Curie point at about 416–450 K and at highertemperatures some residual crystallization are detected.Figure 3a and b shows the Mössbauer spectra obtainedfor samples annealed for 1 h at temperature Top and atTa > Top of the Fe82Nb2B14Y2 and Fe82Nb2B14Tb2 alloy,respectively.Fig. 3. Mössbauer spectra for the Fe82Nb2B14Y2 (a)and Fe82Nb2B14Tb2 (b) alloys, measured at room tem-perature for the samples annealed at temperatures Top(the optimization and at higher temperature).Fig. 4. Magnetic domain patterns obtained the Kerrmicroscopy observations for the Fe82Nb2B14Dy2 (a) andFe82Nb2B14Tb2 (b) alloys annealed at Top = 750 K andTop = 725 K, respectively.918 A. Chrobak et al.One can see that the obtained spectra are typical forthe amorphous phase rich in iron. Similar results areobtained for the Fe82Nb2B14Gd2 and Fe82Nb2B14Dy2alloys. Figure 4a and b show magnetic domain pat-terns obtained by the Kerr microscopy for samples an-nealed at Top for 1 h (the optimization annealing) for theFe82Nb2B14Dy2 and Fe82Nb2B14Tb2 alloy, respectively.One can see that in both cases, the optimized microstruc-ture corresponds to a well-developed large magnetic do-mains characteristic for a magnetic state free of internalstresses.3. Discussion and conclusionsThe results presented in Fig. 1 show that for all ex-amined alloys magnetic permeability can be enhancedby applying 1 h annealing at temperatures Top: 700,725, 725, and 750 K for Fe82Nb2B14Y2, Fe82Nb2B14Gd2,Fe82Nb2B14Tb2 and Fe82Nb2B14Dy2 alloy, respectively.Figure 5 shows Top and the optimized magnetic perme-ability (determined for samples after annealing at Top)versus magnetic momentm of RE additions. One can seethat in relation to a non-magnetic Y addition the tem-perature Top slightly increases with increasing m. Sim-ilar effect was observed in [10] where it was shown thatactivation enthalpy of crystallization as well as crystal-lization heat depend on m in the same way. This meansthat high localized magnetic moment of RE atoms causea slowing down of diffusion processes. Moreover, accord-ing to Figs. 1 and 5 the optimized magnetic permeabil-ity strongly decreases with increasing m which meansthat RE additions cause a hardening of the examinedsoft magnets — the highest effect is observed for alloyswith Tb and Dy. This is understandable because Tb andDy due to a strong spin–orbit coupling introduce to thesystem an additional magnetic anisotropy.Fig. 5. Temperature Top (1 h optimization annealing)and optimized magnetic permeability (determined forsamples after 1 h optimization annealing) vs. magneticmoment of RE additions.The results presented in Fig. 2a–d evidently showthat nanocrystallization of iron in the examined alloystakes place at temperatures higher than 800 K. It is ev-ident that for all alloys the preliminary 1 h annealingat 850 K leads to formation of a composite consistingof iron nanograins embedded into residual amorphousphase. In each case, the thermomagnetic curves do notshow a paramagnetic region as it was observed for sam-ples preliminary annealed at Ta ≤ Top and furthermore,at higher temperatures a residual crystallization is ob-served. These two facts prove that the 1 h optimizationannealing at Top does not lead to the formation of ironnanograins. This conclusion is confirmed by the Möss-bauer spectroscopy measurements. In fact, the spectrapresented in Fig. 3a and b obtained for samples annealedat Top and at temperature higher by 25 K are typical foran amorphous phase rich in iron. The most importantis the fact that for all examined alloys spectra lines typ-ical for iron nanograins (observed usually at velocity ofabout ±6 mm/s) are not detected at all. Finally, tak-ing into account the above arguments one can concludethat the optimized microstructure for the studied fam-ily of amorphous alloys is free of iron nanograins andcorresponds to the relaxed amorphous phase. The mag-netic domain structure, corresponding to the optimizedmicrostructure, as shown in Fig. 4a and b, consists ofregular large magnetic domains characteristic for a mag-netic state free of internal stresses. The case of Tb andDy due to a strong spin–orbit coupling is especially inter-esting. For these alloys the magnetic domain structure,corresponding to the as quenched state is of finger-printtype [9] which means that in this case internal stressesplay a dominant role. Comparing the results obtainedin [9] (see Fig. 6 in [9]) and in the present paper onecan conclude that the 1 h optimization annealing causesa drastic drop down of the internal stresses which mani-fests in a drastic change of the magnetic domain structureand an enhancement of the magnetic permeability.The main conclusions of the present paper can be sum-marized as follows:(i) The low field magnetic permeability of the ex-amined alloys can be significantly enhanced (at leastabout 10 times) by applying a 1h annealing at tem-peratures Top (700 K, 725 K, 725 K and 750 K forFe82Nb2B14Y2, Fe82Nb2B14Gd2, Fe82Nb2B14Tb2 alloyand Fe82Nb2B14Dy2 alloy, respectively. (ii) In all ex-amined cases the optimized microstructure correspondsto the so-called relaxed amorphous phase i.e. amorphousphase with significantly reduced free volume content aswell as internal stresses. (iii) Magnetic domain structurecorresponding to the optimized microstructure consistsof relatively large regular domains indicating low level ofinternal stresses.AcknowledgmentsThis work was supported by National Science Centrein Poland by the grant 2015/19/B/ST8/02636.Optimization of Soft Magnetic Properties. . . 919References[1] M.E. McHenry, M.A. Willard, D.E. Laughin,Prog. Mater. Sci. 44, 291 (1999).[2] G. Haneczok, J. Rasek, Def. Diff. Forum 224-225,13 (2004).[3] T. Kulik, J. Non-Cryst. Solids 287, 145 (2001).[4] J. Marcin, A. Wiedenmann, I. Skorvanek, Physica B870, 276 (2000).[5] O. Zivotsky, K. Postava, L. Kraus, K. Hrabovska,A. Hendrych, J. Pistora, J. Magn. Magn. Mater.322, 1523 (2010).[6] P. Kwapuliński, A. Chrobak, G. Haneczok,Z. Stokłosa, J. Rasek, J. Lelątko, Mater. Sci. Eng. C23, 71 (2003).[7] Ł. Madej, G. Haneczok, A. Chrobak, P. Kwapuliński,Z. Stokłosa, J. Rasek, J. Magn. Magn. Mater. 320,e774 (2008).[8] A. Chrobak, G. Haneczok, D. Chrobak, Ł. Madej,G. Chełkowska, M. Kulpa, J. Magn. Magn. Mater.320, e770 (2008).[9] A. Chrobak, V. Nosenko, G. Haneczok,L. Boichyshyn, B. Kotur, A. Bajorek, O. Zivot-sky, A. Hendrych, Mater. Chem. Phys. 130, 603(2011).[10] A. Chrobak, V. Nosenko, G. Haneczok,L. Boichyshyn, M. Karolus, B. Kotur, J. Non-Cryst. Solids 357, 4 (2011).

Optimization of soft magnetic properties in Fe82Nb2B14RE2 (RE = Y, Gd, Tb and Dy) group of amorphous alloys

Enhancement of soft magnetic properties in the selected group of amorphous alloys was examined by different experimental methods. It was shown that permeability for annealed samples (at T_{a} for 1 h; 300 K < T_{a} < 900 K) plotted vs. T_{a} shows a maximum at which is 700, 725, 725, and 750 K for Fe₈₂Nb₂B₁₄Y₂, Fe₈₂Nb₂B₁₄Gd₂, Fe₈₂Nb₂B₁₄Tb₂ and Fe₈₂Nb₂B₁₄Dy₂ alloy, respectively. For samples after the optimization annealing permeability is at least 10 times higher than in the as-quenched state. The optimized microstructure is free of iron nanograins and corresponds to so-called relaxed amorphous phase

Chrobak, A.

Haneczok, G.

Kansy, J.

Biblioteka Nauki - repozytorium artykuÅÃ³w

Optimization of soft magnetic properties in Fe₈₂Nb₂B₁₄RE₂ (RE = Y, Gd, Tb and Dy) group of amorphous alloys

Лонская, Тамара Федоровна

BSU Digital Library

Типовая учебная программа по учебной дисциплине для специальности: 1-23 01 08 Журналистика (по направлениям), направление специальности 1-23 01 08-02 Журналистика (аудиовизуальная)

Repozytorium Uniwersytetu Śląskiego RE-BUŚ

Title: Optimization of soft magnetic properties in Fe82Nb2B14RE2 (RE = Y, Gd, Tb and Dy) group of amorphous alloys Author: Artur Chrobak, Grzegorz Haneczok, O. Zivotsky, A. Hendrych, Jerzy Kansy, B. Kotur Citation style: Chrobak Artur, Haneczok Grzegorz, Zivotsky O., Hendrych A., Kansy Jerzy, Kotur B.. (2016). Optimization of soft magnetic properties in Fe82Nb2B14RE2 (RE = Y, Gd, Tb and Dy) group of amorphous alloys. "Acta Physica Polonica. A" (Vol. 130, nr 4 (2016), s. 916-919), doi 10.12693/APhysPolA.130.916 Vol. 130 (2016) ACTA PHYSICA POLONICA A No. 4Proceedings of the XXIII Conference on Applied Crystallography, Krynica Zdrój, Poland, September 20–24, 2015Optimization of Soft Magnetic Properties in Fe82Nb2B14RE2(RE = Y, Gd, Tb and Dy) Group of Amorphous AlloysA. Chrobaka,∗, G. Haneczokb, O. Zivotskyc, A. Hendrychc, J. Kansyb and B. KoturdaUniversity of Silesia, Institute of Physics, Uniwersytecka 4, 40-007 Katowice, PolandbUniversity of Silesia, Institute of Materials Science (SMCEBI), 75 Pułku Piechoty 1, 41-500 Chorzów, PolandcVŠB-Technical University of Ostrava, Institute of Physics, 17. listopadu 15, 708 33 Ostrava-Poruba, Czech RepublicdIvan Franko National University of Lviv, Kyryla and Mefodia St. 6, 79005 Lviv, UkraineEnhancement of soft magnetic properties in the selected group of amorphous alloys was examined by differentexperimental methods. It was shown that permeability for annealed samples (at Ta for 1 h; 300 K < Ta < 900 K)plotted vs. Ta shows a maximum at which is 700, 725, 725, and 750 K for Fe82Nb2B14Y2, Fe82Nb2B14Gd2,Fe82Nb2B14Tb2 and Fe82Nb2B14Dy2 alloy, respectively. For samples after the optimization annealing permeabilityis at least 10 times higher than in the as-quenched state. The optimized microstructure is free of iron nanograinsand corresponds to so-called relaxed amorphous phase.DOI: 10.12693/APhysPolA.130.916PACS/topics: 81.07.Bc, 75.50.Tt, 75.60.–d, 76.80.+y1. IntroductionIt is well known that soft magnetic properties of ironbased amorphous alloys can be enhanced by applying aspecific annealing at temperatures close to crystalliza-tion temperature. After such annealing a low field mag-netic permeability can increase even 20 times and a co-ercive field can go down below 1 A/m [1–8]. The ob-served effects are explained by formation of an optimizedmicrostructure which in general can be of two types:(i) iron nanograins embedded into a residual amorphousphase [1–5] or (ii) the so-called relaxed amorphous phasefree of iron nanograins for which free volume and internalstresses are significantly reduced [2, 6–8]. The type of theoptimized microstructure strongly depends on alloyingadditions and parameters of the applied annealing. In-fluence of RE (rare earth) additions with a high localizedmagnetic moment on magnetic properties and crystal-lization of the same group of amorphous alloys in the as-quenched state have been already reported in [9] and [10],respectively. It was shown for example that 2 at.% of REaddition leads to an increase of the Curie temperature byno more than 34 K (for Fe82Nb2B14Gd2) in relation tothe reference Fe82Nb2B14Y2 alloy (TC = 416 K) [9]. Astrong spin–orbit coupling of Tb and Dy atoms leads toan additional magnetic anisotropy of the examined al-loys and to a magnetic hardening (permeability dropsdown about 5 times and a finger-print domain struc-ture appears) [10]. Moreover, a localized magnetic mo-ment of RE atoms cause an increase of the activationenthalpy of crystallization by about 0.8 eV (4.4 eV forthe Fe82Nb2B14Y2 and 5.2 eV for the Fe82Nb2B14Tb2alloy) [10].∗corresponding author; e-mail: artur.chrobak@us.edu.plThe aim of the present paper is to study the optimiza-tion of soft magnetic properties in the family of amor-phous alloys of type Fe82Nb2B14RE2 (RE = Y, Gd, Tband Dy). The key point is to examine an influence ofdifferent thermal annealing on magnetic properties andformation of the so-called relaxed amorphous phase. TheFe82Nb2B14Y2 alloy with non-magnetic yttrium is takenas a reference alloy because Y has similar to RE atomicradius.2. Experimental procedure and resultsThe examined amorphous alloys were prepared by ap-plying a melt spinning technique in a helium atmosphere.The melt was prepared from pure binary REFe2 (RE=Y,Gd, Tb, and Dy) and NbFe2 compounds. The purity ofthe initial metals were : Fe (99.99 wt%), Y (99.96 wt%),Gd (99.96 wt%), Tb (99.96 wt%), and Dy (99.96 wt%).Rare earth metals in a form of binary compounds REFe2and NbFe2 were primarily obtained by the arc-meltingtechnique from metals of the same purity. The obtainedalloys were in the form of strips with thickness and widthof 20–25 µm and 3 mm, respectively. The melt spunribbons in the as-quenched state were annealed at tem-peratures Ta (300 K < Ta < 900 K) for 1 h, and forannealed samples the following measurements were car-ried out: (i) low field magnetic permeability (Agilentmeter E4980a, field 0.5 A/m), (ii) magnetization ver-sus temperature (Faraday type magnetic balance, field0.5 T, 300 K < T < 1100 K, heating rate 5 K/min) and(iii) Mössbauer spectra (standard transmission geometrywith constant acceleration drive). Moreover, for selectedsamples, magnetic domain structure was examined us-ing Zeiss optical microscope adopted for magneto-opticalKerr microscopy.Figure 1 shows the low field magnetic permeabilityµ measured at room temperature for annealed samples(916)Optimization of Soft Magnetic Properties. . . 917Fig. 1. Low field magnetic permeability measured atroom temperature versus 1 h annealing temperature Ta.Fig. 2. Normalized magnetization versus temperaturefor sample preliminary annealed at different temper-atures for (a) Fe82Nb2B14Y2, (b) Fe82Nb2B14Tb2,(c) Fe82Nb2B14Gd2, and (d) Fe82Nb2B14Dy2.plotted versus Ta (for the as-quenched state Ta = 300 K).One can see that in all examined cases µ(Ta) curve showsa distinct maximum indicating that 1 h annealing at awell-defined temperature (denoted as Top) causes a signif-icant enhancement of the magnetic permeability. In fact,according to Fig. 1, annealing at Top results in more thana tenfold increase of µ.Figure 2 shows magnetization in saturation versus tem-perature determined for samples of different alloys inthe as quenched states, after preliminary annealing atTop (the optimization annealing) and after preliminaryannealing at Ta > Top. One can see that for samples inthe as quenched states magnetization drops down withtemperature and at T > 450 K the examined alloysare in paramagnetic state. In temperature range 800 ≤T ≤ 900 Kmagnetization in saturation strongly increasesdue to formation of iron nanograins which was confirmedby X-ray examinations and high resolution transmissionelectron microscopy observations [3]. At temperaturesT > 900 Kmagnetization goes down up to the Curie tem-perature of the already formed crystalline phase. Similarcurves were obtained for samples preliminary annealedfor 1 h at Top i.e. after the 1 h optimization annealing.In contrast, magnetization versus temperature for sam-ples preliminary annealed at temperature Ta = 850 K(i.e. at Ta  Top) do not show an intermediate para-magnetic state. This is obviously due to formation ofiron grains (nanograins) during the preliminary anneal-ing. In each examined case a residual amorphous phasewith the Curie point at about 416–450 K and at highertemperatures some residual crystallization are detected.Figure 3a and b shows the Mössbauer spectra obtainedfor samples annealed for 1 h at temperature Top and atTa > Top of the Fe82Nb2B14Y2 and Fe82Nb2B14Tb2 alloy,respectively.Fig. 3. Mössbauer spectra for the Fe82Nb2B14Y2 (a)and Fe82Nb2B14Tb2 (b) alloys, measured at room tem-perature for the samples annealed at temperatures Top(the optimization and at higher temperature).Fig. 4. Magnetic domain patterns obtained the Kerrmicroscopy observations for the Fe82Nb2B14Dy2 (a) andFe82Nb2B14Tb2 (b) alloys annealed at Top = 750 K andTop = 725 K, respectively.918 A. Chrobak et al.One can see that the obtained spectra are typical forthe amorphous phase rich in iron. Similar results areobtained for the Fe82Nb2B14Gd2 and Fe82Nb2B14Dy2alloys. Figure 4a and b show magnetic domain pat-terns obtained by the Kerr microscopy for samples an-nealed at Top for 1 h (the optimization annealing) for theFe82Nb2B14Dy2 and Fe82Nb2B14Tb2 alloy, respectively.One can see that in both cases, the optimized microstruc-ture corresponds to a well-developed large magnetic do-mains characteristic for a magnetic state free of internalstresses.3. Discussion and conclusionsThe results presented in Fig. 1 show that for all ex-amined alloys magnetic permeability can be enhancedby applying 1 h annealing at temperatures Top: 700,725, 725, and 750 K for Fe82Nb2B14Y2, Fe82Nb2B14Gd2,Fe82Nb2B14Tb2 and Fe82Nb2B14Dy2 alloy, respectively.Figure 5 shows Top and the optimized magnetic perme-ability (determined for samples after annealing at Top)versus magnetic momentm of RE additions. One can seethat in relation to a non-magnetic Y addition the tem-perature Top slightly increases with increasing m. Sim-ilar effect was observed in [10] where it was shown thatactivation enthalpy of crystallization as well as crystal-lization heat depend on m in the same way. This meansthat high localized magnetic moment of RE atoms causea slowing down of diffusion processes. Moreover, accord-ing to Figs. 1 and 5 the optimized magnetic permeabil-ity strongly decreases with increasing m which meansthat RE additions cause a hardening of the examinedsoft magnets — the highest effect is observed for alloyswith Tb and Dy. This is understandable because Tb andDy due to a strong spin–orbit coupling introduce to thesystem an additional magnetic anisotropy.Fig. 5. Temperature Top (1 h optimization annealing)and optimized magnetic permeability (determined forsamples after 1 h optimization annealing) vs. magneticmoment of RE additions.The results presented in Fig. 2a–d evidently showthat nanocrystallization of iron in the examined alloystakes place at temperatures higher than 800 K. It is ev-ident that for all alloys the preliminary 1 h annealingat 850 K leads to formation of a composite consistingof iron nanograins embedded into residual amorphousphase. In each case, the thermomagnetic curves do notshow a paramagnetic region as it was observed for sam-ples preliminary annealed at Ta ≤ Top and furthermore,at higher temperatures a residual crystallization is ob-served. These two facts prove that the 1 h optimizationannealing at Top does not lead to the formation of ironnanograins. This conclusion is confirmed by the Möss-bauer spectroscopy measurements. In fact, the spectrapresented in Fig. 3a and b obtained for samples annealedat Top and at temperature higher by 25 K are typical foran amorphous phase rich in iron. The most importantis the fact that for all examined alloys spectra lines typ-ical for iron nanograins (observed usually at velocity ofabout ±6 mm/s) are not detected at all. Finally, tak-ing into account the above arguments one can concludethat the optimized microstructure for the studied fam-ily of amorphous alloys is free of iron nanograins andcorresponds to the relaxed amorphous phase. The mag-netic domain structure, corresponding to the optimizedmicrostructure, as shown in Fig. 4a and b, consists ofregular large magnetic domains characteristic for a mag-netic state free of internal stresses. The case of Tb andDy due to a strong spin–orbit coupling is especially inter-esting. For these alloys the magnetic domain structure,corresponding to the as quenched state is of finger-printtype [9] which means that in this case internal stressesplay a dominant role. Comparing the results obtainedin [9] (see Fig. 6 in [9]) and in the present paper onecan conclude that the 1 h optimization annealing causesa drastic drop down of the internal stresses which mani-fests in a drastic change of the magnetic domain structureand an enhancement of the magnetic permeability.The main conclusions of the present paper can be sum-marized as follows:(i) The low field magnetic permeability of the ex-amined alloys can be significantly enhanced (at leastabout 10 times) by applying a 1h annealing at tem-peratures Top (700 K, 725 K, 725 K and 750 K forFe82Nb2B14Y2, Fe82Nb2B14Gd2, Fe82Nb2B14Tb2 alloyand Fe82Nb2B14Dy2 alloy, respectively. (ii) In all ex-amined cases the optimized microstructure correspondsto the so-called relaxed amorphous phase i.e. amorphousphase with significantly reduced free volume content aswell as internal stresses. (iii) Magnetic domain structurecorresponding to the optimized microstructure consistsof relatively large regular domains indicating low level ofinternal stresses.AcknowledgmentsThis work was supported by National Science Centrein Poland by the grant 2015/19/B/ST8/02636.Optimization of Soft Magnetic Properties. . . 919References[1] M.E. McHenry, M.A. Willard, D.E. Laughin,Prog. Mater. Sci. 44, 291 (1999).[2] G. Haneczok, J. Rasek, Def. Diff. Forum 224-225,13 (2004).[3] T. Kulik, J. Non-Cryst. Solids 287, 145 (2001).[4] J. Marcin, A. Wiedenmann, I. Skorvanek, Physica B870, 276 (2000).[5] O. Zivotsky, K. Postava, L. Kraus, K. Hrabovska,A. Hendrych, J. Pistora, J. Magn. Magn. Mater.322, 1523 (2010).[6] P. Kwapuliński, A. Chrobak, G. Haneczok,Z. Stokłosa, J. Rasek, J. Lelątko, Mater. Sci. Eng. C23, 71 (2003).[7] Ł. Madej, G. Haneczok, A. Chrobak, P. Kwapuliński,Z. Stokłosa, J. Rasek, J. Magn. Magn. Mater. 320,e774 (2008).[8] A. Chrobak, G. Haneczok, D. Chrobak, Ł. Madej,G. Chełkowska, M. Kulpa, J. Magn. Magn. Mater.320, e770 (2008).[9] A. Chrobak, V. Nosenko, G. Haneczok,L. Boichyshyn, B. Kotur, A. Bajorek, O. Zivot-sky, A. Hendrych, Mater. Chem. Phys. 130, 603(2011).[10] A. Chrobak, V. Nosenko, G. Haneczok,L. Boichyshyn, M. Karolus, B. Kotur, J. Non-Cryst. Solids 357, 4 (2011).

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