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Journal of Magnetism and Magnetic Materials 321 (2009) 3640–3645

Contents lists available at ScienceDirect

Journal of Magnetism and Magnetic Materials

0304-88

doi:10.1

� Corr

E-m

journal homepage: www.elsevier.com/locate/jmmm

Nanocrystals magnetic contribution to FINEMET-type soft magnetic materialswith Ge addition

D. Muraca a,�, J. Silveyra a, M. Pagnola a, V. Cremaschi a,b

a Lab. de Solidos Amorfos, Facultad de Ingenierıa-INTECIN, UBA-CONICET, Paseo Colon 850, C1063ACV Buenos Aires, Argentinab Member of Carrera del Investigador, CONICET, Argentina

a r t i c l e i n f o

Article history:

Received 14 January 2009

Received in revised form

1 July 2009Available online 8 July 2009

PACS:

75.50.Tt

81.07.b 75.75.+a

61.46.w

Keywords:

Nanocrystalline material

Magnetic structure

FINEMET ribbon

Melt spinning

Macroscopic and atomistic magnetization

analysis

53/$ - see front matter & 2009 Elsevier B.V. A

016/j.jmmm.2009.07.005

esponding author. Tel.: +54 43430891.

ail address: diego.muraca@gmail.com (D. Mu

a b s t r a c t

Over the last years several works have been published in which magnetic and structural properties of

soft magnetic nanocrystalline alloys were reported. Among these, there are a series of articles where the

nanocrystals composition of FINEMET-type alloys with Ge addition was obtained by Mossbauer

spectroscopy (MS) and X-ray diffraction (XRD). By considering a linear relationship between the

magnetic moments of the nanocrystals and the composition of various elements in these crystallites,

the magnetic moment of the nanocrystals was calculated. This paper reviews results obtained by

different authors since 1980 and they are compared with ours. In turn, we revised some elements not

previously considered for the calculus of the nanocrystals composition that allowed us to obtain the

magnetic moment of the crystallites in the alloy. In particular, we analyzed FINEMET-type alloys with

replacement of B for Ge: Fe73.5Si13.5Ge2B7Nb3Cu1 and Fe73.5Si13.5Ge4B5Nb3Cu1. The nanocrystalline

structure was obtained by isothermal annealing of melt-spun ribbons at 823 K for 1 h. From MS and XRD

we obtained the atomic composition of the nanocrystals in the magnetic material. The magnetic

contribution of the nanocrystals to the alloy was calculated using a linear model and the results were

compared with experimental measurements of the samples.

& 2009 Elsevier B.V. All rights reserved.

1. Introduction

There has been a great scientific and technological interest onthe development of magnetic materials for more than a century.Throughout these years, soft magnetic properties low coercivityand high permeability have been progressively improved bymodifying the composition and/or structure of ferromagneticalloys.

Coercivity (Hc) and magnetic permeability (mr) are primaryfunction of the magnetocrystalline anisotropy (Kc) of the material.Moreover, an extrinsic magnetic anisotropy is induced by themagnetoelastic effect. Thus, the challenge has been to achievemicrostructures which would reduce both Kc and the saturationmagnetostriction (ls).

The wide range of soft magnetic materials developed with thisaim can be classified into three families: (i) crystalline: with long-range order, (ii) amorphous: with structural short-range order butstill magnetic long-range order and (iii) nanocrystalline: ferro-magnetic nanocrystals embedded in a ferromagnetic amorphous

ll rights reserved.

raca).

matrix with magnetic correlation length larger than mean grainsize.

Although high saturation magnetization (Ms) can be easilyreached in the conventional crystalline materials, when theconcentration of Fe is increased, soft magnetic properties worsenbecause of the high magnetocrystalline anisotropy of a-Fe(K1 ¼ 47 kJ/m3).

In the 1970s, it was discovered that the Kc of the alloys could bedramatically reduced by amorphization. This reduction wasexplained by the random anisotropy model (RAM) [1], becauseof the random atomic arrangement, local short-range magneto-crystalline anisotropies are averaged out over large atomicdistances. Furthermore, there is an exchange coupling betweenthe local moments that causes a long-range magnetic order.Nevertheless, amorphization is not effective in reducing satura-tion magnetostriction; low ls was only obtained in alloys withlow Ms.

In the late 1980s, it was possible to attain low Kc as well asnegligible ls in nanocrystalline Fe-based systems, obtained fromthe partial devitrification of amorphous precursors. The RAMextended by Herzer [2] explained that keeping grain dimensions(D) below the ferromagnetic exchange length (Lex), anisotropicrandom distribution of the nanocrystals homogenously distrib-uted continued to average out. In addition, this composite

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D. Muraca et al. / Journal of Magnetism and Magnetic Materials 321 (2009) 3640–3645 3641

structure leads to the compensation of the magnetostrictionbetween the amorphous (positive contribution) and crystalline(negative contribution) phases, decreasing the magnetoelasticenergy. Therefore, it is possible to have Fe-rich alloys with highsaturation induction (BsZ1.2 T) and excellent soft magneticproperties (Hcr1 A/m; mrZ104) as well.

Two of the main alloy systems in this nanocrystalline magneticmaterials family are FeSiBNbCu [3] and FeZrB(Cu) [4,5], commer-cially known as FINEMET and NANOPERM, respectively. Thehighest effective permeability value was obtained for the formermr(1 kHz)�15.104, with Bs�1.3 T; whereas the latter had themaximum saturation induction, Bs�1.7 T with mr(1 kHz)�3.104. Coaddition to NANOPERM was also studied, giving rise to HITPERM(FeCoZrB(Cu) [6], which has high Curie temperature (TC) for theamorphous and the crystalline phase.

The influence of the addition of Ge to FINEMET-type alloys wasthoroughly studied in the last years [7–12]. Some generalconclusions can be drawn from these works. The MS of the alloyremained independent of the Ge content. The Curie temperature(TC) of the amorphous phase increased with the addition of Ge[7,9,10,13] for all the studied alloys reaching a maximum value of664 K for the Fe73.5Ge15.5B7Nb3Cu1 alloy. This increase wasexplained by the augmentation of the interatomic distancebetween the Fe atoms when Ge is added which enhances theferromagnetic behaviour of the material. The addition of Gelowered the onset of the first crystallization peak for all thestudied alloys while delaying the secondary crystallizationcorresponding to borides precipitation. The replacement of Si orB for Ge reduced the amount of amorphous matrix when heattreated at the same temperature [9,11].

In this work, we present structural and magnetic properties oftwo nanocrystalline FINEMET-type alloys with Ge addition:Fe73.5Si13.5Ge2B7Nb3Cu1 and Fe73.5Si13.5Ge4B5Nb3Cu1. Hyperfineparameters and relative areas of the different possible configura-tions of Fe atoms in the crystallites were obtained by Mossbauerspectroscopy (MS). The hyperfine field was correlated with theisomer shift and compared with previous works published byother authors. The fraction of Fe atoms in the nanocrystalline andin the amorphous phase was also estimated. The lattice parameterof the crystalline phase was obtained by X-ray diffraction (XRD).We revised some elements not previously considered that allowedus to estimate the atomic composition of Fe, Si and Ge in thenanocrystals for each alloy from the lattice parameters resultstogether with Mossbauer data. Finally, from the atomic composi-tion obtained by MS and XRD, we calculated the magneticcontribution of the nanocrystals to the alloy by using a linearmodel and the results were compared with experimentalmeasurements of the samples.

Fig. 1. DO3 structure scheme. A sites are occupied by Fe atoms (grey); D sites are

occupied by Fe atoms (black) and Si or Ge atoms (white).

2. Experimental

High-purity raw materials were used to cast ingots byinduction. The compositions of the alloys were: Fe73.5Si13.5-

Ge2B7Nb3Cu1 (Ge2B7) and Fe73.5Si13.5Ge4B5Nb3Cu1 (Ge4B5).Glassy ribbons, �1 mm wide and �20mm thick, were preparedby the single copper wheel melt-spinning technique in air. Thequenching rate of �106 K/seg avoided the crystallization and theresult was an amorphous structure. This was checked by XRD.

Isothermal annealings of 10-cm-long ribbons were carried outfor 1 h at 823 K in vacuum and the partial devitrification led tonanocrystallized samples.

The structure of the alloys was analyzed by XRD and MS. XRDwas performed at room temperature using a Rigaku diffract-ometer. All scans were run with monochromatic radiation Cu Ka(1.5418 A) and Ni filter. MS was carried out at room temperature in

transmission geometry using a constant acceleration drive and a57Co in Rh source. The calibration was done with an a-Fe foil andisomer shifts (d) are given relative to a-Fe. The spectra were fittedusing the NORMOS program [24].

The MS was measured using a Quantum Design PhysicalProperties Measurement System (PPMS) at 300 K under an appliedfield of 9 T.

3. Results

3.1. Mossbauer spectroscopy

Mossbauer spectroscopy is one of the experimental techniquesused to understand some local properties of these nanocrystallinesystems. When the composition of Si is less than 10% a BCCstructure with partial replacement of Fe atoms for Si is obtained.When the composition is between 10% and 25% the DO3 structurestabilizes, although its coexistence with the BCC structure wasalso suggested [14].

Different fitting procedures for FINEMET alloys have beenreported by several authors [11,14–22]. Some of them [15,16]considered five subspectra, each one consisting of six lines. Four ofthese subspectra corresponded to different Fe sites in the orderedregion of Fe–Si with a DO3 structure and one was related to theamorphous grain boundary phase. T Grafy et al [17] considered sixhyperfine subspectra, with hyperfine fields between 19 and 32 T.They considered three of them associated to Fe atoms with 4, 5and 6 Fe atoms as nearest neighbours, a fourth one associated toFe atoms with 7 and 8 as next nearest neighbours, a fifthsubspectrum associated to a BCC Fe with a small amount ofdissolved Si and the last one associated to other configurations.Rixecker et al [21], considered two phases: an amorphous phasewith a reduced hyperfine field ¼ 16.9 T and the Fe–Si phase withFe3Si structure fitted with six subspectrum. In our case, weconsidered the spectra fitting used by Pradell et al. [14,23] andextended by Moya et al. [11] for FINEMET alloys containing Ge,who used two different sites for Fe atoms in a DO3 structure(Fig. 1). One denoted as A which contains 8 Fe atoms and the otherone denoted as D, that has Fe atoms and Si or Ge atoms. Fe atomsbelonging to A sublattice can have 0–4 Si or Ge nearest neighbours(NN) and 6 Fe atoms as next nearest neighbours (NNN). D sitescan have 0–6 Si or Ge as NNN. Then, An ¼ A(n,0) will represent anFe site belonging to A site with n Si or Ge atoms as NN and none asNNN, while Dn ¼ D(0,n) will represent an Fe atom in D sublatticewith n Si or Ge atoms as NNN and 0 as NN.

The MS fitting was made associating six (S1–S6) and five(S1–S5) subspectra to the Ge2B7 and Ge4B5 nanocrystallinephases, respectively. Two subspectra were used to fit amorphousphases in each alloy. The one with higher Bhf coincided with the

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D. Muraca et al. / Journal of Magnetism and Magnetic Materials 321 (2009) 3640–36453642

typical values previously reported by other authors. On the otherhand, a subspectrum with low field was added for the fitting ofboth alloys. Discussions on this are reported in the discussion ofexperimental results section.

Different possible sites for Fe (A and D) in the spectra of thenanocrystals were considered as previously described (Fig. 2). Theobtained results are summarized in Table 1.

Comparing both Mossbauer spectra it was possible to observethat the relative absorption area of the amorphous phase in Ge4B5(30.53%) was higher than the one corresponding to the Ge2B7

Fig. 2. Room-temperature Mossbauer spectra corresponding to samples Ge4B5 (a)

and Ge2B7 and (b) annealed for 1 h at 823 K. The shaded areas correspond to the

amorphous contribution. The lines correspond to the different Fe sites in the

nanocrystalline phase (S1–S6).

Table 1

Mossbauer parameters related to the amorphous phases and to each of the Fe sites of the

and relative areas (area).

Ge2B7 Ge4B5

D (mm/s) Bhf (T) Area (%) d (mm/s)

0.05 32.6 8.60 0.06

0.07 31.4 11.23 0.09

0.10 29.3 10.70 0.12

0.15 27.5 2.46 0.20

0.19 24,6 19.01 0.21

0.26 19.6 22.88 –

0.13 14.1 23.03 0.25

0.00 4.2 2.09 �0.01

alloy (25.12%). Ge4B5 alloy presented a softer and more centredshape spectrum than Ge2B7 (Fig. 2). From the probability ofoccurrence of each kind of Fe environment (S1–S4 and S5–S6) andusing a binomial distribution [25] the (Si+Ge) content of thenanocrystalline phase was obtained: 20.5% and 21.0% for Ge2B7and Ge4B5, respectively.

Comparing Ge2B7 and Ge4B5 with previously reported alloys[11], an increase of (Si+Ge) amount in the nanocrystals wasdetected (Table 2). The (Si+Ge) nominal composition in these newalloys was greater than the one in the alloys studied by Moya et al.This increase was also observed by Pradell et al [14,23] where thefinal composition of the nanocrystalline phase approached thenominal Fe/Si ratio of the alloy (Fe/(Si+Ge) in our case). Onthe other hand, Fe73.5Ge15.5B7Nb3Cu1 presented lower Geconcentration in the nanocrystals [9] than Ge2B7(Fe73.5Si13.5Ge2B7Nb3Cu1). However, in both cases nominal Bconcentration was 7% and (Si+Ge) was 15.5%. As alreadypublished, this was a consequence of the high crystallizationfraction present in the former nanocrystalline alloy that reducedthe concentration of (Si+Ge) in the nanocrystals [9].

3.2. X-ray diffraction

Lattice parameter of Fe3(Si,Ge) was obtained from XRDmeasurements for both nanocrystallized samples and they werereported in Fig. 3. The observed increase of the lattice parameterwith Ge concentration was consistent with the atomic radii sizedifference between Si and Ge.

It is well known that Si (Ge) shows a linear behaviour betweenits lattice parameter aSi|x (aGe|x) and its composition in a DO3

Fe1�xSix (Fe1�xGex) structure. Taking this into account we canexpect that the lattice parameter a(Si+Ge) of the nanocrystals with x

concentration of (Si+Ge) results from a linear interpolation of thelattice parameters of their constituents aSi|x and aGe|x:a(Si+Ge)|x ¼ (1�y).aSi|x+y.aGe|x; where y is Ge concentration (Fig. 3).

For example, for x ¼ 21% (Ge4B5), being aSi ¼ 21%;Ge ¼ 0% ¼ 2.829A and aSi ¼ 0%;Ge ¼ 21% ¼ 2.880 A (insets (a) and (b) Fig. 3) andconsidering the linear relation between them (Fig. 3), Geconcentration was obtained: y ¼ 5.4%.

Lattice parameter dependence on Si concentration in DO3

Fe1�xSix was taken from [29] (inset (a) Fig. 3). For Ge a linearregression was done with data taken from [9,11,30,31] (inset (b)Fig. 3). Further discussion on this analysis will be presentedby J. Moya.

3.3. Mossbauer spectroscopy and X-ray diffraction

From Mossbauer and lattice parameter results, changes in thenanocrystals composition in FINEMET-type alloys due to thesubstitution of Si for Ge were estimated in some recent works

crystalline phase: Average values of isomer shift (d), magnetic hyperfine field (Bhf)

Bhf (T) Area (%) Subspectra Fe site

32.7 2.70 S1 D0/A0

31.6 7.82 S2 D1–D6

28.6 13.82 S3 A1

24.7 23.91 S4 A2

22.4 21.22 S5 A3

– – S6 A4

19.8 28.98 Am1

5.00 1.53 Am2

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Table 3Room temperature measured magnetization of amorphous and annealed for 1 h at

823 K Ge2B7 and Ge4B5.

Alloy Measured MS

(as-quenched)

(emu/g)

Measured MS

(823 K) (emu/g)Calculated MS

(emu/g)

Ge2B7 139.7 136.1 143.9

Ge4B5 138.9 131.3 140.8

Third column: the crystallites estimated magnetization.

Table 2Nominal atomic fraction of (Si+Ge) in the samples, and (Si+Ge) and Ge amount in

the nanocrystalline phase.

Sample Nominal (Si+Ge)% (Si+Ge)%70.5 Ge%70.5 Ref.

Fe73.5Si13.5B9Nb3Cu1 13.5 18.5 0.0

[11]

Fe73.5Si6.5Ge7B9Nb3Cu1 13.5 18.9 8.8

Fe73.5Si5.5Ge8B9Nb3Cu1 13.5 19.0 10.0

Fe73.5Si3.5Ge10B9Nb3Cu1 13.5 18.6 13.4

Fe73.5Ge13.5B9Nb3Cu1 13.5 18.2 18.2

Fe73.5Ge15.5B7Nb3Cu1 15.5 18.6 18.6 [9]

Fe73.5Si13.5Ge2B7Nb3Cu1 15.5 20.5 2.0

Fe73.5Si13.5Ge4B5Nb3Cu1 17.5 21.0 5.4

D. Muraca et al. / Journal of Magnetism and Magnetic Materials 321 (2009) 3640–3645 3643

[8–12]. In such reports, the approach used did not considervariations on the nanocrystalline lattice parameter of compositionFe1�xSix (Fe1�xGex) when x changed.

With the lattice parameter obtained from XRD and the linearapproach proposed above the composition of Ge in the crystalswas estimated, being 2.0% (70.5%) for Ge2B7 and 5.4% (70.5%)for Ge4B5. Results are shown in Table 2.

3.4. Magnetization and magnetic moment

The MS of the as-quenched and annealed at 823 K alloys weremeasured using a Quantum Design PPMS at 300 K under anapplied field of 9 T. The results are summarized on Table 3.

Based on the Okumura results [35] the magnetic and structuralcorrelation of some FINEMET-type alloys with Ge addition waspreviously studied [8]. Following Okumura’s idea, a linearapproach between the magnetization of the nanocrystals andtheir Si and Ge concentration was made. With data from Table 2and using the model detailed in [8], the magnetization of thenanocrystals of the Ge2B7 and Ge4B5 alloys were calculated andcompared with the measured magnetization of the alloy at roomtemperature (Table 3). The basics to use a linear relation arediscussed in the discussion of experimental results section.

It is well known that the magnetic contribution of these typesof nanocrystalline alloys is the result of both amorphous andnanocrystalline contributions. If we suppose that the massamount of nanocrystals in these alloys is nearly 75%, the magneticcontribution of the amorphous phase could be estimated and wasclose to 112.7 emu/g for Ge2B7 and 102.8 emu/g for Ge4B5.

In a previous work [36], based on the nanocrystalscomposition, obtained from MS, an alloy with the compositionof the remnant amorphous phase was prepared by the melt-spinning technique. The saturation magnetization of this newalloy was measured and its value was assumed to be thecontribution of the amorphous matrix to the original alloy, fromwhere the mass percent of each phase was corroborated.

4. Discussion of experimental results

M. Miglierini and J.M. Greneche [21,22] applied a fittingMossbauer procedure to model the intergranular phase ofFeCuMB (M ¼ Zr, Ti and NbCr) nanocrystalline alloys in their firststages of crystallization.

Four types of Fe atoms were considered to develop the fitting:(i) those belonging to the inner crystalline grains; (ii) Fe atomsthat belong to the nanocrystals but are located in theirsurfaces; (iii) Fe atoms placed in the nanocrystal–amorphousinterface which originate from the amorphous precursor but arein close contact with nanocrystalline grains and (iv) theamorphous residual matrix which is not in direct contact withnanocrystals. Since Fe atoms (ii) and (iii) are almost indistinguish-able from both the structural and the magnetic points of view,they referred to them as the interface. They introduced a modelconsistent of two independent subspectra resulting from thedistribution of magnetic sextets to fit the amorphous residualmatrix and the interface zone. One block with low hyperfine fieldsrepresenting the amorphous residual matrix atoms far from thecrystals (iv) that can be finally decomposed into two components:one consisting of Fe atoms in a paramagnetic state correspondingto the prevailing electric quadrupolar interactions and a secondone consisting of those Fe atoms in a magnetically orderedstate, and a second one attributed to the so-called interface zone((ii) and (iii)).

In our case, the spectra D0/A0, D1–D6, A1, A4 and A4correspond to Fe atoms in the nanocrystals ((i) atoms). Thehigh-field subspectrum used for the amorphous phase (AM1 maybe associated with Fe atoms close to the crystals ((iii) atoms)while the low field was used to fit the Mossbauer spectrumcorresponding to atoms not in direct contact with the nanocrys-tals with Fe–Nb–B composition away from the crystals animpoverished in Fe. This explanation is not conclusive and thishypothesis should be corroborated by other experiments.

We used a linear model to calculate the magnetic contributionof the nanocrystals to the alloy. While this model was imple-mented earlier [8], in this paper, we detailed the arguments thatallowed us its implementation on the basis of results obtained byseveral authors [32–35].

Luborsky and others studied the effect of different metalloidadditions, including Si and Ge, to Fe amorphous alloys [32]. Theypresented the behaviour of the Curie temperature and themagnetic moments for these different systems depending onthe metalloid concentration.

It was observed that the magnetic moment of Fe atomsdiminishes with the concentration of Si and Ge and that the Curietemperature increases with them. The Fe–B–Ge Curie points laysignificantly above the common curve obtained for the rest of theadded elements.

In order to explain the variation of the magnetic moment withthe concentration of Si/Ge when B was replaced, differentsuppositions were done.

As Si and Ge have the same outer electronic configuration, s2p2,one would not expect that the observed changes were the result ofa charge transference phenomenon from the metalloid to thetransition metal [33]. It would not be possible either to justifyit in terms of chemical bond model because these two elements(Si/Ge) have the same electronegativity and first ionizationenergy.

On the other hand, Corb et al. proposed a quantitative model tocompute the change in the magnetic moment of crystalsformed by transition-metalloids metals (M-T) [33]. The modelwas based on chemical bonding and accounted the magneticmoment variation in Co–M, Ni–M and Fe–M alloys. Excellentresults were obtained on the basis of this model for Co and Ni.

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Fig. 4. Bhf as a function of n corresponding to An. Results obtained by other

authors are also plotted [26,27].

Fig. 5. Is (d) of different alloys vs Bhf. Results obtained by other authors are also

plotted for comparison [14,26,27]. Estimated errors were 0.5 for the Bhf and 0.01

for the d.

D. Muraca et al. / Journal of Magnetism and Magnetic Materials 321 (2009) 3640–36453644

Nevertheless, this model predicted a null change of the magneticmoment of Fe atoms in the BCC lattice due to the metalloidspresence. This is because the bonded levels in the Fe band do nothave uncompensated spins. In a later work, Corb reported that themagnetic moment variations, resulting from the addition ofmetalloids to the Fe structure, came from possible changes inthe lattice parameter and, as a consequence, a modification of theinteratomic distances [34]. Hence, the change in the magneticmoment due to different metalloids on Fe alloys could beexplained in terms of the Bethe–Slater curve as metalloids modifythe distance and the coordination number between magneticatoms (Fe–Fe).

Recently, Okumura et al. [35] presented a magnetic andstructural study of Si-rich FINEMET alloys. They obtained acorrelation between the magnetization measurements of thesample in its nanocrystalline state and the magnetic momentcalculus at atomic level of the nanocrystals. Taking into accountthe nanocrystalline volumetric fraction they estimated thecrystalline magnetic contribution to the alloy. On the basis ofthe results obtained by Corb et al. [33] and [34], Okumuraproposed a linear model of the magnetic moment change of thenanocrystals as a function of the Si content in the crystallites.

In view of all these experimental results, we used a linearmodel to obtain the magnetic contribution of the nanocrystals tothe nanocrystalline alloys which was presented in the previoussection (magnetization and magnetic moment) in Table 3.

In Fig. 4 Bhf as a function of n corresponding to An (an Fe sitebelonging to A site with n Si or Ge atoms as NN and none as NNN)was plotted and compared with works presented by otherauthors. As Crisan et al. [26], we also found a linear relationbetween Bhf and An, although not with the same constant rate.

Using the Mossbauer technique Dubiel et al. studied the effectof the substitution of Si and Ge for a series of Fe–Si and Fe–Gealloys, on Bhf and d [28,29]. In these works, they attributed thechanges of Bhf and d to changes in the spin and charge density,respectively, due to the Fe atom substitution for Si or Ge in theBCC Fe structure. On the one hand, the Bhf of 3d systemsmeasures the density of s electron spins so the change in thisvalue is due to the change in this density. On the other hand, the ISmeasures the density of s electrons in Fe nuclei. The resultsobtained by Dubiel and Zinni [28,29] showed the change in thedensity of s electrons and s electron spins with Si (Ge)concentration. From the experimental data they correlated thechange in the average value of Bhf with the change in the averagevalue of d, obtaining a linear relation between them. Thiscorrelation can be explained through two possible phenomena:

1.

Fig(a)

Changes in the spin and charge density of itinerant electrons.

. 3. Lattice parameter dependence (a) with Ge content in Fe1�x(Si,Ge)x. Insets:

a vs. Si content in Fe1�xSix, (b) a vs. Ge content in Fe1�xGex.

2.

Changes in the spin and charge density at Fe nuclei due to Siatoms located in the vicinity of the atom.

Dubiel concluded that the observed spin and density are twofirst approximation linearly correlated. The simplest explanationwould be that only electrons of one spin state are mainly involvedin the redistribution [28].

In Fig. 5, Bhf was plotted against d. As can be seen, there is alinear relation between d and Bhf. A dashed line was added just toshow the trend of this correlation. Results of other authors wereshown for comparison.

From these linear relation between the Bhf with the d and theBhf with n, we could expect that only electrons of one spin stateare mainly involved in the redistribution and, as reported byDubiel et al [28,29], the impurity character of Ge and Si atoms inthe Fe crystalline structure can be considered as a ‘‘spin hole’’effect.

5. Conclusions

This paper reviews results obtained by different authors since1980 and they are compared with ours. In turn, we revised someelements not previously considered for the calculus of thenanocrystals composition that allowed us to obtain the magneticmoment of the crystallites in the alloy. In particular, magnetic andstructural properties of two soft magnetic alloys Fe73.5Si13.5-

Ge2B7Nb3Cu1 and Fe73.5Si13.5Ge4B5Nb3Cu1 with nanocrystallinestructure were presented.

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From Mossbauer analysis, the correlation between the Bhf andd was obtained. MS showed that after annealing Ge2B7 at 823 Kfor 1 h, 74.88 at% of Fe was present in the crystalline phasewhereas the remaining 25.12 at% was present in the amorphousmatrix. In Ge4B5, 69.47 at% of Fe was found in the crystallinephase.

Improving a former linear model, the content of (Si+Ge) in thecrystals was estimated to be 20.5 at% for Ge2B7 and 21.0 at% forGe4B5, while Ge concentration was 2.0 at% and 5.4 at%, respec-tively.

We calculated the magnetic contribution of the nanocrystals tothe alloys using a linear model and the results were related withexperimental measurements of the samples.

Acknowledgments

This work was supported by the Ministerio de Ciencia,Tecnologıa e Innovacion Productiva (MinCyT), Universidad Nacio-nal de Buenos Aires (UBA) and the Red Nacional de Magnetismo(Argentina). The authors gratefully acknowledge Dra. BibianaArcondo, Dr. Javier Moya and Dra Claudia Rodriguez Torres fortheir help in analyzing Mossbauer spectra.

References

[1] R. Alben, J.J. Becker, M.C. Chi, J. Appl. Phys. 49 (1978) 1653.[2] G. Herzer, in: K.H.J. Buschow (Ed.), Handbook of Magnetic Materials, vol. 10,

Elsevier Science, 1997, p. 415.[3] Y. Yoshizawa, S. Oguma, K. Yamauchi, J. Appl. Phys. 64 (1988) 6044.[4] K. Suzuki, N. Kataoka, A. Inoue, A. Makino, T. Masumoto, Mater. Trans. JIM 31

(1990) 743.[5] K. Suzuki, A. Makino, A. Inoue, T. Masumoto, J. Appl. Phys. 70 (1991) 6232.[6] M.A. Willard, D.E. Laughlin, M.E. McHenry, D. Thomas, K. Sickafus, J.O. Cross,

V.G. Harris, J. Appl. Phys. 84 (1998) 6773.

[7] V. Cremaschi, G. S�anchez, H. Sirkin, Physica B 354 (1–4) (2004) 213 31.[8] D. Muraca, V.J. Cremaschi, J. Moya, H. Sirkin, J. Magn. Magn. Mater. 320 (6)

(2008) 810.[9] D. Muraca, V. Cremaschi, J. Moya, H. Sirkin, J. Magn. Magn. Mater. 320 (9)

(2008) 1639.[10] D. Muraca, V.J. Cremaschi, H. Sirkin, J. Mag. Mag. Mater. 311 (2007) 618.[11] J.A. Moya, V.J. Cremaschi, H. Sirkin, Phys. B. 389 (2007) 159.[12] A. Saad, V. Cremaschi, H. Sirkin, J. of Met. Nanocryst. Mater. 20–21 (2004) 717.[13] A. Puszkarz, M. Wasiak, P. Uznanski, P. Sovak and Marek Moneta. ION 2008

Conference in Kazimierz Dolny, Sent Vacuum, Elsevier, Poland.[14] T. Pradell, N. Clavaguera, Jie Zhug, M.T. Clavaguera-Mora, Phys.: Condens.

Matter 7 (1995) 4129.[15] G. Hampel, A. Pundt, J. Hesse, J. Phys.: Condens. Matter 4 (1992) 3195.[16] M. Garcia del Muro, R. Zqiak, X. Battle, J. Parellada, JMMM (1995) 140.[17] T. Graf, M. Kopcewicz, J. Hesse, J. Phys.: Condens. Matter 8 (1996) 3897.[18] A. Gupta, N. Bhagat, G. Principi, A. Hernando, JMMM (1994) 29147.[19] J.M. Borrego, V.A. Pena Rodriguez, A. Conde, Hyperfine Interact. 110 (1997) 1.[20] T. Liu, Z.X. Xu, J.Y. Ping, R.Z. Ma, Hyperfine Interact. 108 (1997) 401.[21] G. Rixecker, P. Schaaf, U. Gonser, J. Phys.: Condens. Matter 4 (1992) 10295.[22] M. Miglierini, J.M. Greneche, J. Phys.: Condens. Matter 9 (1997) (2303 and

2321).[23] T. Pradell, J. Zhu, N. Clavaguera, M.T. Clavaguera-Mora, J. Appl. Phys. 83 (10)

(1998) 5171.[24] R.A. Brand, Normos Program, Internal Report, Angewandte Physik, Universitat

Duisburg (1987).[25] G. Rixecker, P. Schaaf, U. Gonser, Phys. Status Solidi (a) 139 (1993) 309.[26] O. Crisan, J.M. Greneche, J.M. Le Breton, A.D. Crisan, Y. Labaye, L. Berger, G.

Filoti, Eur. Phys. J. B 34 (2003) 155.[27] Josefina Marıa Silveyra; Victoria J Cremaschi; Javier A Moya; Emılia Illekov�a;

Marco Coısson; Federica Celegato; Paola Tiberto; Franco Vinai. Sent to Matt.Sc. and Eng. B September 10, 2008 (Ms. Ref. no.: MSB-D-08-01432).

[28] S.M. Dubiel, W. Zinn, J. Magn. Magn. Mater. 28 (1982) 261.[29] S.M. Dubiel, W. Zinn, Phys. Rev. B. 28 (1) (1983) 67.[30] M. Richard Bozorth, Ferromagnetism, Six Printing, D. Van Nostrand Company,

New Jersey, Toronto, New York, London, 423.[31] R. Sobzcak, Monatsh. Chem. 106 (1975) 138.[32] F.E. Luborsky, J.L. Walter, E.P. Wohlfarth, J. Phys. F: Met. Phys. 10 (1980) 958.[33] B.W. Corb, R.H. O0Hanley, N.J. Grant, Phys. Rev. B. 27 (2) (1982) 636.[34] B.W. Corb, Phys. Rev. B. 31 (4) (1984) 2521.[35] H. Okumura, D.E. Laughlin, M.E. McHenry, J. Magn. Magn. Mater. 267 (2003)

347.[36] D. Muraca, J. Moya, V.J. Cremaschi, H.R.M. Sirkin, Phys. B 398 (2007) 325.