Magnetic After Effects and Magnetostriction of Fe-Base Metallic Glasses
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MAGNETIC AFTER EFFECTS AND MAa9JETCSTRICTION OF FE-BASE METALLIC GZASSES A.K. COLLINS, R.C. O'HANDLEY AND N.J. GRANT Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139 ABSTRACT Magnetic after effects (MAE's) have been studied in Fe-base and Co-base Fe-base amorphous alloys shcw large MAE's due in part to
metallic glasses.
the high magnetoelastic energy (large Xs) whereas Co-base alloys exhibit much smaller MAE's due to their low magnetostriction. A detailed study of the acntribution of the magnetoelastic energy to the MAE's was done on the Fe83-xCrx B17 and Fe83-xNbx B17 glass systems. INTROWUCTICN The magnetic after effect of the permeability (disacccmodation) is cbserved in both crystalline and amorphous ferrcimagnets. In both cases the nature of the effect is structural. In crystalline materials the magnetic relaxaticn is due to alignment of well defined defects or impurities with the magnetization direction[1,21.
This process has a discrete activation energy and it takes place within a narrow temperature range. In amorphous alloys •owever, the nature of the defects is less well defined and the migration of the defect structures is characterized by a broad spectrum of activation energies. Consequently, the temperature range over which the relaxation takes place is broad as well[3]. In both crystalline and amorphous materials the free energy of the system (ferrcmagnet and defect) can be expressed as a sua of the elastic, magnetoelastic, and anisotropy energy[4]. The defect alignment process during magnetization changes all three of these contributions to differing degrees. In this paper we report the contribution of the magnetoelastic energy to the MAE's in Fe-base alloys.
A detailed study was performed on the
Fe 8 3 x CrxB1 7 and Fe83-xNbxB17 glass systems.
These glass systems were chosen because they are based mostly on one transition metal, Fe, and they show a variation in the saturation magnetostriction constant X from 30 x 10-6 to 2 - 3 x 10-6 as a function of Cr or Nb content. EXPERIMENTAL Two series of amorphous alloys Fe 8 3 pared by melt spinning. ing. Mat. Res. Soc. Symp. Proc. Vol. 58.
Cr B17 and Fe 8 3
Nb B1 7 were pre-
The anorphous state was identified by X-ray scatter-
1986 Materials Research Society
164
Magnetic relaxation was measured using a Gen Rad Digibridge after the sanple's initial state w0as set by application of a dc saturating pulse[5]. The isothermal relaxation w,•as measured for T varying between 259C and 3009C. ;'he isochronals were constructed using 6P )
I [tI] - ]dt 2] 1[tl]
(1)
Where pi[t 1 ] and p [t 2 ] are the permeability values at tI
= 20 sec and t2=
60 sec. Magnetostriction measurements were performed bv means of the strain gauge method and the magnetization was measured by using a vibrating sample magnetometer.
Fram the magnetization versus temperature behavior we ob-
tained the Curie temperature values. RESULTS AND DISCUSSION The isochronal relaxation spectra
of amorphous Fe
Si
and
1.5
1.0
0.
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