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Physica Scripta

Magnetic and Mössbauer study of Fe-V-B-Si amorphous metallic ribbons

To cite this article: A Habiballah et al 1997 Phys. Scr. 56 112

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Physica Scripta. Vol. 56, 112-116, 1997

Magnetic and Mossbauer Study of Fe-V-B-Si Amorphous Metallic Ribbons

A. Habiballah,’ G. Marest,’* E. H. Sayouty,’ H. Lassri3 and R. Krishnan4

Laboratoire de Physique Nuclkaire. Universite Hassan

II,

Facultt des Sciences A b Chock, B.P. 5366 Maarif, Route d’El Jadida,

km-8,

Casablanca, Institut de Physique Nucleaire, Universite Claude Bernard Lyon I, F-69622 Villeurbanne, France.

Laboratoire de Physique des Matbriaux et de Micro-Blectronique. Universite Hassan 11, Facultk. des Sciences Ain Chock, B.P. 5366 M a a s , Route d’El Laboratoire de Magnetisme et d’Optique de 1’Universitk. de Versailles, Batiment FERMAT, 45, Avenue des Etats-Unis 78035 Versailles cedex, France.

Morocco.

Jadida,

km-8,

Casablanca, Morocco.

Received July 29,1996; revisedform received September 20,1996; accepted November 18,1996

Abstract

The inhence of the addition of a few atomic percents of V on the crys- tallization temperature, and the magnetic properties of amorphous iron- boron-silicon alloys were investigated using magnetic measurements and Mossbauer spectroscopy. With an increasing V content, the crystallization temperature increases, but the Curie temperature and the magnetic moment of the Fe atom decrease. We have extracted the local random anisotropy from the coercive field. The crystallization of the amorphous Fe,,V,B,,Si, alloys was studied after vacuum annealing between 600 and 800 K for one hour.

An

analysis of the Mossbauer spectra along with sup- porting X-ray diffraction measurements are presented. The crystalline pro- ducts of these amorphous alloys proceed from bcc-FeSi, t-Fe,B and o-FeB phases.

1. Introduction

A major class of amorphous alloys which have been studied extensively is formed between the transition metals T (T

=

Fe, CO, Ni) with other elements of the transition metals M ( M

=

Mn, Cr, V, Ti, MO,

,

. .). and the metalloid elements M e ( M e

=

B, C, Si, P, . . .). These alloys are gener- ally produced as amorphous solids by rapid quenching from the liquid state. Many efforts have been made to study the influence of the solute elements M substitution in Fe-based amorphous alloys [l-31. The magnetic properties and the structural relaxation of these magnetic amorphous alloys have been studied mainly by magnetic measurements and Mossbauer spectroscopy. The addition of M to metallic glasses is considered important because it improves their soft-magnetic properties. The study of the structural relax- ation of these amorphous alloys caused by annealing shows one-or-two stage development. From the results of the annealing effect on the Mossbauer spectra, it has been reported that the structural relaxation of the amorphous Fes4-,V,BI6 shows a one stage development [4].

In order to study the influence of the addition of V on the various magnetic properties of amorphous Fe-B-Si alloy such as the magnetic moment of Fe, Curie and crys- tallization temperature, coercive force and local anisotropy constant, we have prepared amorphous Fe,,~,V,B,,Si,

*

The author to whom all mail should be sent.

56

alloys with 0 < x < 13.7. Their magnetic and crystallization properties were investigated by Mossbauer spectroscopy and X-ray diffraction measurements.

2. Experimental

Amorphous Fe,,~,V,B,,Si, ribbons have been prepared by the melt spinning technique in pure argon atmosphere. The amorphous state was verified by X-ray diffraction and the composition was analysed by electron microprobe. Magne- tization measurements were carried out using a vibrating sample magnetometer (VSM) in the range 4.2 to 300K. The Curie temperature T, and the crystallization temperature T, were also determined from the temperature dependence of the magnetization between 300 and 1000K in a weak field (100Oe). A heating rate of 10K/min was used. Conversion electron Mossbauer spectra were determined at room tem- perature with the use of a flowing He-5% CH, gas pro- portional counter in which the sample was placed in backscattering geometry. The ’Co(Rh) source was mounted on a constant acceleration triangular motion velocity transducer. The velocity scale and all the data are referred to metallic a-Fe absorber at room temperature. For spectra analysis a programme developed by Le Caer et al.

[5] was used in which hyperfine field distributions are con- sidered. The amorphous Fe,,V,B &, alloy was annealed at different temperatures between 600 and 800K for one hour. Structural data were also obtained from X-ray diffrac- tion measurements with CuK, radiation (1

=

1.5418A).

3. Results and discussion 3.1. Magnetic studies

The Curie temperature T, and the crystallization tem-

perature T, of amorphous Fe,,~,V,B,,Si, alloys as a func-

tion of V concentration, are shown in Fig. 1. As seen from

the figure, T, decreases with increasing solute content, while

T, increases. The decrease in T, is due to the decrease in the

Fe content which also leads to a decrease in the coordi-

nation number. The increase in T, indicates better thermal

stability of the amorphous state with the addition of V.

(3)

Magnetic and Mossbauer Study of Fe- V-B-Si Amorphous Metallic Ribbons 113

2

Y

0

300 I

I I

,

0 ,

0 4

8

12 16

v (XI

Fig. 1 . V concentration dependence of

T.

and

T, .

Figure 2 shows the magnetic moment of Fe (pFe) as a function of the V content. pFc decreases with the solute element concentration as it has already been found for MT-M-B-Si alloys where M T

=

Fe, CO, Ni and M

=

Cr, Mn, V, . .

,

[2, 6, 71. The decrease of the magnetic moment is essentially attributed to hybridization effects and the charge transfer phenomenon arising from B and Si. The linear decrease from 1.66 pB for x

=

0 to 0.71 pB for x

=

13.7 for the magnetic moment measured at 4.2K (Fig. 2) can be explained in terms of the Friedel virtual bound state model

P I

anisotropy constant and one can write

H , = (1/20)K4d6/A3Mo (2)

where d

=

R,, is the characteristic correlation length of anisotropy directions defined earlier [lo-111. We take R ,

=

10% which was determined experimentally on similar alloys. The exchange constant follows from the relation [12]:

A

= csFe kB

q/4(1 +

SFc)rFeFe

(3)

where C is the iron concentration, S,, is the spin of Fe, and

i F e F e ,

the interatomic distance, is taken as 2.5 A.

From the experimental H, values we calculated the random local anisotropy constant and the results at 300K are shown in Fig. 3. H, gradually increases with increasing V content but the local anisotropy constant (KL) shows a small decrease.

M-H loops for amorphous Fe,,V,B,,Si, are shown in Fig. 4 together with the loops obtained for the alloy annealed at T,

=

800 K. The coercitivity values measured at room temperature are 5 Oe and 170 Oe for the amorphous and annealed Fe,,V,B,,Si, alloys respectively. Coercivity and hysteresis losses increase for both materials when crys- tallization has occured. These data indicate that the absence of granular structure in amorphous ferromagnets reduces H,. The coercivity of amorphous Fe,,~,V,B,,Si, alloys increases rapidly with increasing annealing temperature, depending on the V concentration. For example, the coer- civity field H, is constant up to 700K but increases from lOOe up to 175Oe between 700K and 800K in the case of the Fe,,V,B,,Si, alloy.

P = pmatrix

- 4 1 0

-

Az)

where

pmatrix

is the moment per atom in the matrix and AZ is the atomic number difference of the solute relative to the matrix (AZ

=

3 for Fe-V).

As regards the anisotropy, Alben and Becker [9] have developed a theory which relates the coercivity to the local

(l) 3.2. Mossbauer studies

Figure 5 shows the Mossbauer spectra and the correspond- ing hyperfine field distributions P(H) of the amorphous Fe,,~,V,B,,Si, alloys for 3 < x < 13.7. The spectra are characteristic of spectra obtained for ferromagnetic amorp- hous alloys. They exhibit broadened lines due to a distribu-

2’5 i

0

0 * t 4 . 2 K

0 0

0

-1

Fig. 2.

300K+

0.5 1

0 0

0 1

0 4 8 12 16

V concentration dependence of pFc at 4.2 K and 300 K.

A

&

3

8

Fig. 3.

e o

r

*

0 I I

2 5 8 11 14

x (VI

V concentration dependence of H, and K, at 300K.

(4)

114 A. Habiballah, G. Marest, E. H . Sayouty, H . Lasmi and R. Krishnan

h

3

W

cd

c

.>

-2 -1 0 1 -

H

(IO-'

T)

-& 3

-1 0 i

.-i

H

(10.'

T)

Fig. 4. M-H loops registered at 300K for amorphous Fe,,V,B,,Si,, before (a), and after crystallization (b).

tion of the hyperfine field parameters. Because of the structural disorder, firstly the quadrupolar shift is assumed to be zero and, secondly, each magnetic domain is assumed to have the same hyperhe field distribution which therefore does not depend on the magnetic texture. The angle 8 between the hyperhe field and the y-beam is given by the ratio of the intensities of lines A ,

=

12,5/11,6

=

413 sin28/

(1 + cos20). The spectra, which are practically symmetrical about the centroid, were fitted with a distribution of hyper- fine fields only. As 8 changes from 0 to go", the ratio A , increases from 0 to 4/3. For a completely random distribu- tion of magnetic moments, A ,

=

2/3. Table I gives the isomer shift (IS), the average hyperfine field ( ( H ) ) , the stan- dard deviation

(bH)

and the ratio A , as a function of the V concentration. It is clear that the increase in the V content leads to a decrease of both the isomer shift and hyperfine field values. The reported values for A , show that the iron moments are mainly randomly oriented. Many similarities exist between the results obtained with our Fe,,~,V,B,,Si, samples and the Fe,,~,Cr,B,,Si, alloys studied by Srivinas et al. [13]. A low field component grows in the P(H) dis- tribution when the V content increases as was the case for

O 0 * O 2 K

O

0 "

* 0 2

..

h

-5 0 5

t

0.005

o-IiE 0

0 10 20 30

Fig. 5. Conversion-electron Mossbauer spectra at room temperature and corresponding P ( H ) for amorphous Fe,,~,V,B,,Si, alloys with 0 6 x 6 13.7.

Cr. The mean value of the magnetic hyperfine field decreases versus the V content at a rate of 1T/ at% V, comparable to the rate 1.5T/ at% Cr measured by Srivinas et al. [13]. This decrease could be due either to the decreasing Fe concentra- tion consecutively to the addition of V atoms or to the decrease of the Curie temperature.

The critical concentration x, for magnetic ordering was found from the Mossbauer study, x,

=

25 at% V, in very good agreement with the value x,

=

22 at% V deduced from the magnetic measurements. They are similar to the value x,

=

24 at% V obtained from magnetic measurements for Fe,,~,V,B,,Si,, amorphous alloys [2]. The variation of the magnetic moment of iron as a function of the average

Table I. Hyperfine parameters at room temperature for amorphous F e 8 0 ~ x V x B l , S i 8 alloy. The standard deviation on I S is k 0.01 mm/s and on A , is f 0.10

X (H)

IS

al? A,

0 h l / S )

cn

3 22.0 0.08 5.0 1.10

6 18.4 0.08 6.9 0.92

8 17.2 0.06 7.0 0.94

10 15.0 0.06 8.6 0.90

13.7 9.5 0.00 8.6 0.85

(5)

Magnetic and Mossbauer Study of Fe-V-B-Si Amorphous Metallic Ribbons 115

dl

0 0

40 50 60 70 80 90

2 9 (degrees)

Fig. 6. X-Ray diffraction patterns for amorphous Fe,,V6Bl,Si, alloy: (a) as-quenched; (b), (c), (d) after annealing at 700, 750 and 800K, respectively (0, Fe-Si, 0 , Fe,B,

*,

FeB).

Table 11. Mossbauer parameters of the crystalline phases and sites in Fe7,V6BI2Si8 alloy after annealing at 750K and 800 K . The standard deviation on I S is & 0.03 mm/s and on H is k0.3 T for the crystalline components and f 0 . 6 T for the amorphous part respectively

Annealing Relative

temperature (H) I S intensity Phase

T,

(K)

0 ("b) ex4

assignment

33.2 0.00 34 Fe-Si

31.4 0.04 27.4 0.1

750 25.5 0.2s 2 Fe,B

22.3 0.1

10.9 0.1 7 FeB

5 0.3 V-rich boride

Amorphous 21.2 0.07 55

33.0 0.0 57 Fe-Si

31.0 0.04 27.4 0.1

800 25.5 0.1 9 Fe,B

22.3 0.1

10.9 0.1 10 FeB

23.4 0.07 24 Amorphous

5 0.3 V-rich boride

0.02 0

0.02 0

0.02 0 0.02

0 0.02 0

;

5

aC ' .

.. . .. ,

T,

= 700 K

-S -6 -4 -2 0 2 4 6 S Velocity (mm.s-l)

Fig. 7. Conversion-electron Mossbauer spectra of Fe,,V,B,,Si, annealed at 600,650,700,750 and 800 K, respectively.

hyperfine field was found to be linear. The calculated ( H ) / p F c ratio is about 13.3 TIPB, similar to what is nor- mally observed in amorphous Fe8,B,, alloys [14]. The results deduced from magnetic and Mossbauer spectroscopy measurements are in a good agreement.

3.3. The crystallization process

Figure 6 shows X-ray diffraction patterns taken for the Fe74V6B,,Si8 sample before heat treatment and after annealing at 700, 750 and 800K. This alloy starts crystalliz- ing at 750K and the crystalline to the amorphous volume ratio gradually increases with annealing temperature.

Finally, after annealing at 800 K bcc-FeSi, tetragonal Fe,B and orthorhombic FeB are clearly identified.

Figure 7 displays the conversion electron Mossbauer spectra registered for the as-quenched sample and after

Physica Scripta 56

(6)

116 A. Habiballah, G. Marest, E. H . Sayouty, H. Lasmi and R. Krishnan

thermal treatment at 600, 650, 700, 750 and 800K. The lowest temperatures bring no change in the Mossbauer spectrum while after 750 K annealing some crystalline phases are detected. Thus the fit procedure was carried out considering a superposition of a continuous distribution of hyperfine fields due to the amorphous part and of discrete fields representative of the crystalline phases. At 800 K the sample is almost completely crystallized. The hyperfine parameters obtained after fitting the spectra corresponding to a sample annealed at 750 K and 800 K are summarized in Table 11. If the amorphous part represents 55% of the spec- trum at 750 K, it decreases to 24% after annealing at 800 K.

Seven sets of six line patterns have been introduced to fit the crystalline part of the spectra. The three highest components (33 T, 31 T, 27 T) correspond to bcc Fe-Si phase with differ- ent environments for iron atoms (8, 7, 6 iron nearest- neighbour respectively) as proposed by Haggstrom et al.

[l5]. The hyperfine fields with 25.5T and 22.3T can be compared with the values for the tetragonal Fe,B [16]

phase and the existence of a (Fe, V),B can be proposed. The two lowest fields at 10.9 T and 5 T could be attributed to the FeB phase [17] and V-rich boride with paramagnetic char- acter, respectively.

4. Conclusion

In conclusion we have prepared amorphous Fe-V-B-Si alloys and carried out magnetization and Mossbauer studies at room temperature. The substitution of iron atoms in Fe,,B,,Si, amorphous alloys by vanadium atoms causes changes in the magnetic moment of Fe, Curie and crys- tallization temperatures, coercitive force and random local anisotropy constant. It was found that when the V content increases, the crystallization temperature and the coercitive field increase whereas the Curie temperature and the iron magnetic moment decrease. A critical concentration of 21 at% V to obtain magnetic ordering has been deduced. A

study by Conversion-electron Mossbauer spectroscopy shows that the hyperfine parameters ( ( H ) , IS) decrease with increasing V content. The transformation from the as- quenched amorphous to the crystalline state of amorphous Fe,,V,B,,Si, alloys is detected. The crystalline phases bcc- FeSi, t-Fe,B and o-FeB are formed.

Acknowledgements

The authors wish to express their thanks to Dr. H. Ouahmane from CNRS de Meudon, for the loop hysteresis measurements and to Dr. A. Bouam- rane from INSA de Lyon for the X-ray diffraction measurements.

References

1 Chen, H.

S., IEEE

Trans. Magnetic

12,933 (1976).

2.

Rao,

K. V.,

Steinback, M., Liebermann, H. H. and Barton, L., J. Appl.

Phys.

53, 7795 (1982).

3. Krishnan, R.,

Dancygier, M. and Tarhouni, M., J. Appl. Phys.

53, 7768 (1982).

4.

Zemcik, T., Pavlovsky, J. and Jakesova, M., Hyperfine Interactions

27, 345 (1986).

5.

Le

Caer, G. and Dubois, J. M., J. Phys.

E12,1495 (1979).

6.

Ohnuma,

S.

and Matsumoto, T., J. Appl. Phys.

50,7597 (1979).

7.

O'Handley, R. C., Solid St. Commun.

38,703 (1981).

8. Friedel, J., Nuovo Cimento, suppl, to vol.

3,287 (1958).

9.

Alben, R. and Becker, J. J., J. Appl. Phys.

49,

3

(1978).

10.

Hassanain, N.,

Lassri,

H.,

Krishnan,

R. and Berrada, A., J. M a p . Magn. Mater.

146, 315 (1995).

11. Lassri, H., Habiballah, A., Sayouty,

E.

H. and Krishnan, R., to be published in J. M a p . Magn. Mater.

12.

Hassanain, N., Lassri, H., Krishnan, R. and Berrada, A., J. Magn.

M a p . Mater.

146,37 (1995).

13. Srivinas,

V.

et al., Hyperhe Interactions

34,495 (1987).

14.

Nakajima, T., Kita,

E.

and Ino, H., J. Mater. Sci.

23, 1279 (1988).

15. Haggstrom, L., Grana, L., Wapphg, R. and Devanarayanan,

S.,

Physica Scripta

7, 125 (1973).

16. Le

Caer, G. and Dubois, J. M., Phys. Stat. Solidi

A64,275 (1981).

17.

Cooper, J. D., Gibb, T. C., Greenwood, N. N. and Parish, R. V., Trans. Faraday Soc.

60,2097 (1964).

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