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STRESS AND MAGNETIC FIELD DEPENDENCES
OF THE SATURATION MAGNETOSTRICTION IN
Co-RICH AMORPHOUS ALLOYS
A. Hernando, M. Vázquez, J. Barandiarán, W. van Hattum
To cite this version:
JOURNAL DE PHYSIQUE
Colloque C8, Suppldment au no 12, Tome 49, ddcembre 1988
STRESS AND MAGNETIC FIELD DEPENDENCES OF THE SATURATION
MAGNETOSTRICTION IN Co-RICH AMORPHOUS ALLOYS
A. Hernando (I), M. Vkquez (I), J. M. Barandiarh (2) and W. J. van Hattum (I) (I) Dpto. Fisica de Maten'ales, F. Fisicas. U. Complutense, 28040, Madrid, Spain
(2) Dpto. Electricid~d y Electr6nica, F. Ciencias. U. Pais Vasco, 48080, Vizcaya, Spain
Abstract.
-
As has been recently shown the magnetostriction constant, A,, of nearly zero magnetostriction Co-rich amorphous alloys depends on applied stress. It is shown here that this dependence also occurs at 77 K. Furthermore a noticieable dependence of A, on the magnetic field is reported.Introduction
The magnetostriction constadt A, of some Co-rich amorphous alloys exhibit very low values (order of magnitude of
lo-'
or even less). These alloys can be obtained by adding small amounts of some metals (e, g, Fe) to the Co-based glass [I, 21. They are very interest- ing since they allowed us the study of the dependence of A, on some variables as quenching rate and struc- tural relaxation [3, 41. Some of them exhibit a peculiar temperature dependence with compensation tempera- ture below the Curie point indicating the contribution to A, of different mechanisms [I, 51.More recently, it has been shown that A, decreases upon applied stress at a typical rate of 10-lo Mpa-' [6, 71. It has been interpreted as produced by local atomic rearrangements produced by the applied stress [8]. The aim of this work has been to study in further detail the influence of applied stress and magnetic field on A,.
Figure 1 shows the evolution of
~ 2 ' ~
with the ap- plied tensile stress keeping constant the magnetic field Hz = 1 600 ~ m - l and H, = 40 ~ m - ' , at room tem- perature. The axial field was high enough to produce saturation of the magnetization in the longitudinal di- rection when neither transverse field nor tensile stress are applied.As can be observed the slope of the
v2;ll2
versus 0, instead of being constant as predicted by equation (2), changes sign for a close to 200 MPa. This effect which corresponds to a change of sign of the magnetostriction on a is originated by the previously reported stress dependence of A,[?I.
Experimental and discussion
The studied sample was a ribbon of ( C O O . ~ ~ F ~ O . O ~ ) , , S ~ ~ B B ~ ~ obtained by single-roller quenching technique. Their dimensions were 21 pm
thick and 0.55 mm wide. Experiments were performed lo 200 i400 o(MPa) J600 800 by measuring the voltage V2, induced in a pick-up coil
wounded around the ribbon when a saturating dc axial
field Hz, a tensile stress, a, and a small ac transverse Fig. 1.
-
v2i112 is plotted as a function of g. field, Hy sin w t , were simultaneously applied [9, 101:H,"
(1) A new result, which has not been reported before as far as we know, is that shown in figure 2. v2i112
has been plotted as a function of Hz with applied stress as a parameter. According to equation (2) a A being a constant. In our measurements Hy is held
constant, thereby equation (2) can be rewritten as linear behavior of vc112 versus H z , with B as propor- tionalitv constant was exwected. However the deriva-
B being a constant.
tive of k;l12 respect to H, rises linearly with a, for (2) Hz > 2 000 ~ r n - ' , which indicates that A, in the high stress range possesses a term proportional to Hz in equation (2).
JOURNAL DE PHYSIQUE
Fig. 2. - VL'/~ as a function of Hz for different a values. Note that the slopes of the straight lines increase as a does. The linear behavior appears a for Hz above 2 000 ~ r n - ' .
Therefore the results plotted in figures 1 and 2 leads to write A, as
where ASo is the magnetostriction value extrapolated a t zero applied both stress and magnetic field. a and b are positive and from the experimental results their values are 10-lo Mp8-I and 10-lo ( ~ m - ' ) - ' respectively.
Two important remarks must be emphasised, i) the stress and field dependence of A, has been observed in all composition checked with nearly-zero magnetostric- tion and ii) the qualitative characteristics of this de- pendence do not exhibit any change by lowering the temperature up to liquid nitrogen. Figure 3 shows v ~ L ~ / ~ as a function of a for different
Hz
values. The measurements were performed a t 77 K on a sample of composition ( C O ~ . ~ ~ F ~ ~ . ~ ) , ~ Si15B10. This behavior ob- served at low temperature allows us to disregard any thermally activated process to account for the stress and field dependence of A,. .It will be shown in detail in a paper in preparation that the coexistence of two amorphous phases, elasti- cally coupled, with different magnetostriction to each other leads to the stress and field dependence of A, reported here.
Fig. 3.
-
v$/~ as a function of a as measured at 77 K for (Co0.~5Fe0.05),~ Si10B15 composition.Acknowledgments
This work has been supported 'by the CAICYT project PA840365 and by the Comit6 Conjunto Hispano-Norteamericano project CCA8411006
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