Journal of Magnetism and Magnetic Materials 196-197 (1999) 154-155
~ i ~ Journalof magnetism ~ i ~ and magnetic materials
The influence of heat treatment on the Barkhausen effect in the Fe-Cr-B amorphous alloy L. Ceniga a'*, L. Novfik b, 1~. Kisdi-Kosz6 c "Institute o f E.~perimental Physics. Slot:ak Academ.v oJ'Science.~', Watsonova 47, 043 53 Ko~ice, Slol~ak Republic" hDepartment (?l"Ph3'sics, Technical Uni~:epwit3,, Komenskg'ho Park 2, 041 20 KoSice, Slovak Republic' ~MT,4 KFKI Rex. Inst. ,[br Materials Sci., P.O. Box 49, H-1525 Budapest, Hungat 3'
The analysis of the Barkhausen noise power spectrum, the coercive force and the Barkhausen impulse density is applied to a study of heat treatment influence on remagnetization process and amorphous structure of the F e - C r - B amorphous alloy. ((", 1999 Elsevier Science B.V. All rights reserved. K e v w o r d s . Barkhausen effect; Annealing; Coercitivity; Amorphous alloy; Fe-Cr-B
The Barkhausen effect (BE) is a direct consequence of domain wall interactions with microstructural defects and then can give detailed information on material structure. The BE has been used to explain amorphous structure changes caused by heat treatment. The FeTv.4Cr6.sBt~.l amorphous alloy has been prepared in a form of 10mm wide and 20p, m thick ribbons by a single roller method. The conventional X-ray technique has been used to check the ribbon amorphicity. The strip-shaped samples of 15 cm length have been isothermally annealed in argon protective atmosphere for I h at the 5°/min coolling rate. Barkhausen impulses as induced Barkhausen jumps have been taken-offby the single-layer pick-up coil of 100 turns and 10 mm length. The samples have been magnetized in a liner time course external field of 1000 Am -~ amplitude and 1 mHz frequency. The power spectrum, SO*) , of (V 2 Hz-1) dimension, has been always registered at the external field equal to the sample coercive force. The analysed frequencies have ranged from 20 Hz up to 150kHz at the 54dB/octave decay of a filter transmission band. The coercive force has been
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determined by a computer-controlled F6ster magnetometer. The dependence of the coercive force, He, on the annealing temperature, T, is shown in the Fig. 1. The Hc concave decrease in the range to about 250':C may be characterized by short-distance diffusion (SDDI of amorphous matrix atoms. The SDD process has caused more homogeneous atom density that has led to inner stress decrease. The Hc convex course above 250':'C has been a result of long-distance diffusion (LDD) of the Cr and B atoms. The LD D process has led to form areas of which different atom concentration has been suitable for crystallization. The different atom concentration areas have been responsible for inner stress increase. The Hc rapid increase above 300'C has been connected with crystalization process that has formed crystallic grain in the different atom concentration areas. Barkhausen noise parameters as well as the coercive force are a function of E(x) gradient whereby the energy, E(x), is not influenced by the external magnetic field but material structure . The course of the E(x) gradient consists of potential barriers to be a reason of domain wall jumps. The more homogeneous atom density as a result of the heat treatment has caused disintegration of higher potential barriers into smaller ones. The
0304-8853/99/$ - see front matter 'i2' 1999 Elsevier Science B.V. All rights reserved. PIE S 0 3 0 4 - 8 8 5 3 ( 9 8 ) 0 0 6 9 8 - 2
L. Ceniga et al. / Journal of Magnetism and Magnetic Materials 196-197 (1999) 154-155
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-3.0 ~ 2.6-
E .2.5 <
i .... 50
i .... 150
i .... 200
j .... 250
Fig. 3. The Barkhausen noise power spectrum.
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Fig. 1. The coercive force and the Barkhausen impulse density vs. the annealing temperature.
A i ....
. . . . . . . .
200 ° C
300° C .
H JAm-1 ]
Fig. 4. The Barkhausen impulse density during the remagnetization process.
0.2 d 0.1 0.0 , . , . . , . , , 200 300 100
, , = . ~ 500
Fig. 2. The Barkhausen impulse density distribution at the 15 000 x amplifing and the 100 turn pic-up coil.
disintegration has been responsible for the increase of the Barkhausen impulse density (BID), rlmax(Fig. 1), and BID distribution, n . . . . . (Fig. 2), by the annealing temperature increase. These parameters mean the total BI number per a volume unit and the BI n u m b e r of the U voltage size per a volume unit, respectively. The BID (Fig. 4) and the BID distribution have been measured during the magnetizing along one branch of a magnetic loop and the nmax and n . . . . . represent the BID and the BID distribution after the getting of the magnetization maximum value for H > 60 A m - 1. The Barkhausen noise has changed by the annealing temperature increase the way that the contribution, n . . . . . /n . . . . of voltage-small and voltage-high BIs, under
and above about 200 mV (Fig. 2), has increased and decreased to be connected with the increase and the decrease of the power spectrum, S(f) (Fig. 3), above about 50 kHz and in the 0.4-50 kHz frequency range, respectively. Fig. 4 shows the dependence of the BID during the remagnetization process. It can be seen that the BID has been almost constant above 60 A m - 1 of the external magnetic field intensity, H, so the contribution of domain wall irreversible motion to the total magnetization has been significant in the range to approximately 60 A m - 1. The above mentioned results have shown the relation between the coercive force and the Barkhausen noise parameters of the F e - C r - B amorphous alloy in the heat treatment process.
 A. Zentkov~t, A. Zentko, Acta Phys. Slov. 30 (1980) 313. 1-2] E. Kneller, Ferromagnetismus, Springer, Berlin, 1962, p. 366.