346 Journal of Magnetism and Magnetic Materials 41 (1984) 346-348 North-Holland, Amsterdam

AE-EFFECT AND INTERNAL FRICTION IN Co-S i -B METALLIC GLASSES

Lech Tomasz BACZEWSKI, Zbigniew KACZKOWSKI, Erazm LIPII~SKI

Polish Academy of Sciences, Institute of Physics, al. Lotnik6w 32/46, 02-668 Warsaw, Poland

The measurements of AE-effect, internal friction, magnetomechanical coupling, piezomagnetic stress sensitivity and incremental permeability were investigated as a function of the bias magnetic field for the metallic glasses of the composition C072SixB2S. x where 5 < x ~ 17 and for Coy (Sio.33Bo.77)xoo.y where 72 ~< y ~ 78.

1. Introduction 3. Results and discussion

Metalfic glasses exhibit AE behaviour [1] and posses an exceptionally large magnetomechanical coupling [2] which value is a measure of the con- version of elastic energy into magnetic energy and vice versa. The relative change of Young's mod- ulus in a magnetic field can reach values as high as AE/E - 4.5 for Fe8oB15Si 5 [3] or AE/E = 2.36 for Fes1Si3BtsC a [4].

2. Experimental

Metallic glasses of composition Co725ixB28.x ,

where 5 ~ x ~ 17 and COy(Si0.33B0.77)100.y , w h e r e

72 ~ y ~ 78, were prepared in the form of long ribbons by the single-roll rapid quenching method. The amorphous state of the ribbons was confirmed by X-ray diffraction. The measurements were car- fled out on the samples of the length 60 ram, 1 mm wide and 30 to 50 /tm thick. The resonance-antiresonance method [5] and the auto- mated motional impedance circle method [6] have been used for the determination of the frequencies of the mechanical resonance fro, magnetomechani- cal resonance fr, antiresonance fa, and quadrantal frequencies fl , f2 [7]. The measurements were car- ried out at room temperature and the amplitude of the magnetic field was 0.8 A /m. The samples were demagnetized by a 35 Hz magnetic field with an amplitude of 10 kA/m. The AE-effect, the inter- nal friction Q-1, and magnetomechanical coupling coefficient k were calculated from these dynamical results [5-7]. The incremental permeability/tlr wa calculated from the impedance measurements at the frequencies 20 kHz (well below resonance frequency).

AE behaviour of Co-Si-B metallic glasses are presented in fig. 1. Values of A E-effect (Es-E o)/E o are about 1.5% and are much lower than the high AE-effect observed for Fe-Si -B metallic glasses [8], The values of AE-effect can be calculated from the observed values of the initial permeability go, saturation magnetostriction X s, magnetic polariza- tion I s and Young's modulus at saturation state Es, using Kersten's formula for the initial permea- bility [9]. Amorphous metallic glasses have no long range structural order and because of that the anisotropy is very small. When the anisotropy is small the initial permeability is given by [9]:

20 # aE /~r = 97~2sE s Eo • (4)

F-F o E.

1

o

l Co7~ Sis Ba '~ -3 I

0 '.0 80 120 H [-~,X.] Fig. 1. AE-effect for Co-S i -B metallic glasses.

0304-8853/84/$03.00 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)

L T. Baczewski et al. / AE-effect and Q - z in C o - S i - B alloys

Table 1 Calculated and measured values of A E / E o

347

Alloy k ~ E s I s #1T A E / E o ca[c A E / E o obs ( |0 -6) (GPa) (T) ( - ) (%) (%)

Co72Si7B2] - 3.0 163 0.69 2560 1.7 0.6 COTs Sis.s Bl6.s - 4.4 162 0.85 2500 2.4 1.2

The values of AE-effect calculated in this way are k

listed in table 1. The highest calculated AE-effect 0.15 A E / E o = 2.4~o is obtained for Co78Sis.sBt6.s alloy which has the highest saturation magnetostriction (?% = -4.4 X 10 - 6 ) [10]. All the investigated al- loys exhibit the minimum of Young's modulus 0.10 dependence as a function of magnetic field, i.e. the "negative" AE-effect (fig. 1). The negative AE-ef- feet occurs in the weak magnetic field below 100 0.05 -- A/m. In the same region, where Young's modulus shows a minimum, the internal friction shows a maximum (fig. 2). AE-effect and the internal fric- tion are connected with the change of domains 0 structure during the magnetization process. The theory proposed by Smith and Birchak [11] can be used for the interpretation of the internal friction and AE-effect. This internalstress-distribution the- ory predicts that the internal friction is caused by magnetomechanical hysteresis as the result of the irreversible domain walls motions [11]. The depen- dence of magnetomechanical coupling coefficient k and the incremental permeability for the free vibrating sample as a function of the bias mag-

Co~2Si~ Bz~ ,( ~ , ~ Co,Sissies o

B I - - Co?2Sir/BI1 +

2 co~si,z B,6 l,,

80 120 H [A/m]

Fig. 2. The internal friction dependence on the bias magnetic field for Co - S i - B metallic glasses.

CoT~Si~ I~ o --Co72Si v B~ 6

~o 8o 12o H [~/m] Fig. 3. The magnetomechanical coupling coefficient depen- dence on the bias magnetic field for C o -S i -B metallic glasses.

netic field is shown in figs. 3 and 4. The largest value of magnetomechanical coupling was ob- served for Co78Si5.sB]6.5 (k = 0.17). The values of the initial permeability #~, for Co-Si-B metallic glasses are between 2500 to 3000. The piezomag- netic stress sensitivity coefficient [12] as shown in fig. 5, has the maximum in the weak magnetic field

~° J C%Si121~, 2500 " ~ k "C%Si~l~ +

C%Si~sB~s o 2000 ~ k , x . C%Si~ I~ :

Co~ Siss B~. s

I000

500 ~ ~ ,

0 /-,0 80 120 H [A/m]

Fig. 4. The incremental permeability as a function of the bias magnetic field for C o -S i -B metallic glasses.

348 L T . Baczewski et aL / AE-effect and Q - i in C o - S i - B alloys

d /

CO,I~Si 7 BI2~ x - - C%~Si6.sB~ o-

C%S~sB~ o C%2Si~ Bn ~-

15 I " : Co72Si~ B16

5

0 8o 120

Fig. 5. The piezomagnetic stress sensitivity coefficient as a function of the bias magnetic field for Co-Si-B metallic glasses.

22 n W b / N shows that Co-S i -B metallic glasses are less sensitive to mechanical stress than are F e - S i - B alloys. The highest AE-effect, magneto- mechanical coupling and piezomagnetic stress sensitivity were observed for Co78BI9.sSi6.5. The calculated values of the AE-effect obtained from Kersten's formula have the same order of magni- tude than the measured values. It seems that smaller measured AE-effect values than calculated ones arise from the large "negative" A E-effect which is not taken into consideration in Kersten's formula. The second reason for this is that the saturation of magnetostriction is not achieved for used magnetic polarization. The estimated values of magnetostriction from the d - H curve are 1.4 to 1.8 x 10 -6 when the measured saturation magne- tostriction is in the range from 3 to 4.4 x 10 -6.

below 50 A / m , and it decreases rapidly in the higher magnetic field. The values of the piezomag- netic stress sensitivity coefficient obtained for Co -S i -B metallic glasses (dma x = 22 n W b / N ) are rather small in comparison with the values of d in Fea0B15Si 5, where dma x = 70 n W b / N for the rib- bon in the as quenched state and d = 170 n W b / N after annealing in transverse magnetic field [3]. The values of the magnetostriction estimated from the area under the d - H curve in fig. 5 for Co -S i -B are roughly between 1.4 and 1.8 x 10 -6.

4. Conclusions

Maximum internal friction is connected with the irreversible domain walls motions arising from the magnetization process. The "negative" A E-ef- fect was observed. The values of A E / E o = ( E s -

E o ) / E o for Co-S i -B are lower than 1.5%. The piezomagnetic stress sensitivity coefficient dma~ =

References

[1] H.S. Chen, Rep. Progr. Phys. 43 (1980) 353. [2] P.M. Anderson III, J. Appl. Phys. 53 (1982) 8101. [3] M. Brouha and J. van der Borst, J. Appl. Phys. 50 (1979)

7594. [4] K.I. Arai and N. Tsuya, Sci. Rep. Res. Inst. Tohoku Univ.

A28 (1980) 247. [5] Z. Kaczkowski, Arch. Electr. 11 (1962) 635. [6] T. Walecki, RENIOM 80, eds. J. Ilczuk and J.W. Morofl

(Uniwersytet Sl~ski, Katowice, 1981) p. 199. [7] Z. Kaczkowski and E. Lipifiski, Anelastic phenomena and

migration after effect in solids states, eds. J. Ilezuk and J.W. Morofi (Uniwersytet Sl~ski, Katowice, 1983).

[8] M.A. Mitchell, A.E. Clark, H.T. Savage and R.J. Abbundi, IEEE Trans. Magn. MAG-14 (1978) 1169.

[9] M. Kikuchi, K. Fukamichi, T. Masumoto, T. Jaglehfiski, K.I. Arai and N. Tsuya, Phys. Stat. Sol. (a) 48 (1978) 175.

[10] L.T. Baczewski and T. Jagielihski, IEEE Trans. Magn. MAG-17 (1981) 2692.

[11] C.W. Smith and J.R. Birchak, J. Appl. Phys. 40 (1969) 5147.

[12] Z. Kaczkowski, J. Magn. Magn. Mat. 41 (1984) 338, 341.