THE EFFECT OF APPLIED STRESS ON THE POWER LOSS, DYNAMIC MAGNETOSTRICTION AND DOMAIN BEHAVIOUR OF INDIVIDUAL GRAINS OF SILICON-IRON IN A POLYCRYSTALLINE MATRIX

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THE EFFECT OF APPLIED STRESS ON THE POWER LOSS, DYNAMIC MAGNETOSTRICTION

AND DOMAIN BEHAVIOUR OF INDIVIDUAL GRAINS OF SILICON-IRON IN A

POLYCRYSTALLINE MATRIX

D. Mapps, G. Simmons, J. Thompson

To cite this version:

D. Mapps, G. Simmons, J. Thompson. THE EFFECT OF APPLIED STRESS ON THE

POWER LOSS, DYNAMIC MAGNETOSTRICTION AND DOMAIN BEHAVIOUR OF INDIVID-

UAL GRAINS OF SILICON-IRON IN A POLYCRYSTALLINE MATRIX. Journal de Physique Col-

loques, 1971, 32 (C1), pp.C1-386-C1-387. �10.1051/jphyscol:19711133�. �jpa-00213951�

JOURNAL DE PHYSIQUE

Colloque C 1, supplement au n° 2-3, Tome 32, Fevrier-Mars 1971, page C 1 - 386

THE EFFECT OF APPLIED STRESS ON THE POWER LOSS, DYNAMIC MAGNETOSTRICTION AND DOMAIN BEHAVIOUR

OF INDIVIDUAL GRAINS OF SILICON-IRON IN A POLYCRYSTALLINE MATRIX

D. J. MAPPS (*) Ph. D., B. Eng. (Tech.), G. H. SIMMONS (**) Ph. D., B. Eng. (Tech.), and J. E. THOMPSON, Ph. D., C. Eng., F. Inst. P.,

Wolfson Centre for the Technology of Soft Magnetic Materials, U. W. I. S. T., Cardiff, U . K.

Résumé. — On a mesuré par une méthode thermique la perte de puissance des grains individuels de Fe-Si dans un échantillon polycristallin ainsi que le mouvement des parois par effet Kerr. On a étudié l'effet d'une tension

(0 ± 7 X 10« N.mr

)

sur la perte de puissance et le mouvement des parois. , , „ , , „ On a determine l'effet d'une tension et d'une compression apphquees perpendiculairement au plan de 1 echantillon

sur la magnetostriction dynamique. On a developpe un modele base sur la structure des domaines observee, qu'on a verifie par des mesures supplementaires.

Abstract. — The power loss of individual grains of silicon-iron in a polycrystalline sample has been measured using a thermal method, and the domain wall motion studied by the Kerr magneto-optic technique. The effect of applied stresses (0 ± 7 x 10

N.m-2) on both the power loss and domain motion has been investigated.

The effect of both compressive and tensile stresses applied in two perpendicular directions in the plane of the sheet on the dynamic magneto-striction has been determined. A theoretical model based on the observed domain structure has been developped to explain the experimental results ; and a verification of the proposed model has been attempted by making additional measurements.

1. Introduction. — Grain-oriented silicon-iron is used in large quantities by the electrical engineering industry. In many cases, the properties of the material and its behaviour in a device or product are consi- derably different from the properties of the material as produced in sheet form. One basic cause of this change arises from the elastic stresses applied, often inadvertently, to the material during construction of the device. In recent years, this has been understood but some applied stresses are unavoidable.

Consequently, a detailed investigation has been carried out on the effects of stress applied both along and at right angles to the rolling direction on the power loss, dynamic magnetostriction and the domain behaviour of both polycrystalline samples and indi- vidual crystals in the samples ; using techniques deve- loped over the last few years.

2. Experimental Apparatus. — The power loss in individual grains was measured using the «rate of temperature rise » method [1].

This apparatus enabled domain wall movements to be observed in the same grain using the Kerr magne- to-optic effect [2]. Stress ( + 7 x 10

N.m"

) could be applied to specimens both along and at right angles to the rolling direction. A rosette strain gauge attached to the underside of the grain enabled the strain within the grain to be measured, and a single turn search coil wound through two small holes near to the grain boundaries made possible measurement of the rele- vant flux density.

Satisfactory methods for the measurement of the variation of the dynamic magnetostriction with applied stress in both polycrystalline samples and individual grains have been described elsewhere [3].

(*) Now with the Data Recording Instrument Company, U. K.

(**) Now with the Hatfield Polytechnic, U. K.

3. The Experimental Results. — The variation of power loss with strain for one grain is given in figure 1 for two conditions ; firstly without a controlled magnetising waveform ; and secondly, with the magne-

POWER LOSS w»Ul Icj"'. ci l-S W r

STRAIN

C O M P R E S S I O N TENSION

STRRm

•40 -«o -20 COMPRESSION

20 *0 TENSION

FIG. 1. — The power loss at 1.5 Wb. irr

and 50 Hz for various values of stress applied either in the rolling direction or perpen- dicular to the rolling direction. A controlled waveform.

• uncontrolled waveform.

tising waveform controlled to give a sinusoidal flux waveform in the test grain. In previous experiments, the flux waveform in a sequence of grains had been compared with the total flux waveform across the

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19711133

THE EFFECT OF APPLIED STRESS ON THE POWER LOSS, DYNAMIC MAGNETOSTRICTION C 1 - ³⁸⁷

sample. It had been found that whilst the total flux waveform might be sinusoidal, the waveform in indi- vidual grains might be far from sinusoidal and indeed the flux densities might be some i 20 % different from the average.

Kerr domain observations showed that there was a remarkable correlation between the loss curves and domain changes in the grains with both longi- tudinal and transverse stresses. In the region A to B, a bar pattern of domains parallel and antiparallel to the rolling direction was found. From B to C , the spacing of the bar pattern increased and gives an increased loss as might be expected from the theories of Lee [4] and Pry and Bean 151. At point D, domain stress patterns [6] appeared and these gradually covered more and more of the crystal as the stress increased causing the power loss to increase rapidly.

(Fig. 2) shows the variation of the 50 c/s dynamic magnetostriction with stress for two other grains.

The points A' and B' on figure 2 mark the points at which changes in domain structure occurred.

FIG. 2. - The dynamic magnetostriction at 1.5 Wb . m-2 and 50 Hz is shown for grains I and I1 for various values of compres- sive stress applied in the rolling direction.

measured values

with error. --- computed graph, see text.

4. Dynamic Magnetostriction at High Stresses. - A simple theoretical model has been developed to explain the magnitude and variation of the magne- tostriction with high applied stresses (above point B' in figure 2). This was based on the << stress pattern I type [6] and involved the accurate measurement of the dependence of the spacing of the [OOl] and [OOl]

domains on the applied stress. The theoretical curve is shown in figure 2.

5. Dynamic Magnetostriction at Low Stress Levels.

A simple theory (to be published in detail) has been developed to account for the relatively large negative values of dynamic magnetostriction at zero and low stress levels. A formula can be obtained relating the magnetostriction A111 to the misorientation 8, yaw (in silicon-iron both the roll and pitch are small, the greatest variation is found in the yaw), viz.

where

- B < l

B, (cos 8 + ^{sin 8 )}

In order to test equation (l), Epstein samples were cut a t various angles to the rolling direction from high quality Goss-oriented material. The experi- mental results are plotted in figure 3.

FIG. 3. - The variation of the dynamic magnetostriction AI - with I misorientation angle for silicon-iron. The measured points are the results obtained from samples cut at various angles to the rolling direction. The solid curve was computed from equa-

tion (1).

6. Conclusions. - (i) The stress sensitivity of the power loss has been measured for single grains in silicon-iron at 1.5 Wb.rn-. and 50 Hz with longi- tudinal and transverse stresses. The loss variations with stress can be correlated with domain changes in the individual well aligned grains.

(ii) The effect of stress on the dynamic magneto- striction of two individual grains has been determined.

Based on domain pattern observations a simple model has been proposed to account for the negative magneto- striction often found at low stress levels.

-The variation with low stresses of the dynamic (iii) As a test of the proposed model, the magneto- magnetostriction of individual grains has been shown striction has been measured on a number of poly- to vary considerably from grain to grain, and such crystalline samples cut at various angles to the rolling variation is well known in polycrystalline samples. direction and reasonable agreement has been found.

References

[l] OVERSHOTT (K.) and THOMPSON (J.), Proc. I. E. E., [4] LEE (E.), Proc. I. E. E., 1958,105C, 337.

1970, 117, 865. [5] PRY (R.) and BEAN (C.), J. Appl. Phys., 1958 ( S ) , [2] MAPPS (D.) and THOMPSON (J.), to be published. 30, 532.

[3] SIMMONS (G.) and THOMPSON (J.), PYOC. I. E. E., [6] DIJKSTRA (L.) and MARTIUS (U.), Rev. Mod. Phys.,

1968, 115, 1835. 1953, 25, 146.