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MAGNETOMECHANICAL DAMPING AND
DOMAIN STRUCTURES IN GRAIN ORIENTED
SILICON STEEL SHEETS
K. Haga
To cite this version:
M A G N E T O M E C H A N I C A L D A M P I N G A N D D O M A I N S T R U C T U R E S IN G R A I N O R I E N T E D S I L I C O N S T E E L S H E E T S
K. Haga
The Ins Litute o f Physical and Chemical Research, Wako-Shi, Saitama, 351. Japan
~ b s t r a c t . - The relation between magnetomechanical damping and magnetic domain structures in highly grain oriented commercial silicon steel sheets has been investigated by the torsion pendu- lum method o f Collette's type as functions of magnetic field, tensile stress and crystallographic orientation. The domain pattern on the specimens is consisted o f main 180" domain and a small quantity of supplementary domain structures. The changes in magnetomechanical damping occurring by means o f the applica- tion of tensile stress to the sheets with different orientations are proportional to the amount of supplementary domains and also magnetic softness. In the specimen with the angle of 55" to the rolling direction, of which the longitudinal axis coincides with
[Ill], the damping capacity was the highest. It was verified, from the results of a coating effect on magnetomechanical damp- ing, that the formation of glass film on the sheet's surface is equivalent to the application of tensile stress of 30-40 ~g/crnZ.
1. Introduction.- It is generally well known that magnetomechanical damping has it's source in the irreversible movement of magnetic domain boundary due to vibrational stress. Although the nature of the damping in ferromagnetic materials has hitherto been studied by a number of workers, relatively little work [I]-[13] has been reported on the direct relation between the damping and the actual magnetic domain structures in these materials.
The purpose of the present work is to describe the damping in terms of magnetic domain structures and magnetic propertis as para- meters o f applied tensile stress, insulated coating and crystallogra- phic orientation using the highly grain oriented commercial silicon steel sheets with a simple domain structure.
2. Experiment.- The material of the specimens used was commercial grain oriented sheets of G - 8 grade [14] with high permeability which is called HiB-8 made by Kippon Steel Co. In the case of damping measurement, the specimens were flat pieces 1 2 0 ~ 1 5 ~ 0 . 3 mm in size, where the long sides were at diffrent angles of 0, 35, 55, 70 and 90" with respect to the rolling direction of the sheets, then stress- relief-annealed at 800°C in N2 gas. Their long axis coincides with
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the crystallographic direction [001] for @ = O O , [Ill] for 9=5S0 and [I101 for @=go0, in the plane (110). The damping tests were carried out at vibratory frequency o f about 0.8 c/s, at maximum strain amplitude of about 1 ~ 2 0 x 1 0 - 5 , at room temperature, using the torsion pendulum rnetod of Collette's type. Before each damping tests, the specimens were always demagnetized by applying a.c. magnetic field of
1
50 Hz. The magnetic damping AQ-, is given from the difference between internal friction in the demagnetized state Q-A and in the state of
-
1magnetic saturation Q of d.c. magnetic field of about 350 Oe. The static tensile stresses o f OslOO ~g/cm' were applied to the direction of a longitudinal axis in the specimens using a spring ballance. No Snoek peak was found for the specimens because of high purity.
In the measurement o f magnetic properties, the specimens were wound into a torroidal form having an outdiameter o f 45 mm, then ann- ealed at 800°C in N2 gas. D.c. magnetization was undertaken with
ballistic galvanometer method, and magnetic core loss was made by wattmeter method [IS]. Magnetic domain structure o n the specimen's surface was observed with Kerr-optical apparatus [16]. The specimens used in this case were machined from the identical material with that measured in the damping test, and were 30x10 mm in size, then careful- ly mechanical polished and annealed at 800°C in vacuum. Magneto- striction was measured with a strain gauge method.
3. Results and Discussion.- The changes o f damping capacity in the magnetic field are shown in Fig.1 for the random oriented specimens of grade S - 9 and the conventional grain oriented ones G - 1 2 in addition to the highly grain oriented G - 8 , and those magnetic properties are given in Table 1. For grade S - 9 an improvement o f magnetic properties such as permeability and coecive force obtained by high temperature annea- ling, due to the purification [17], resulted in high damping capacity and the strong magnetic field dependence. Such phenomena, an analogy between magnetic softness and damping capacity, has been so far found by many researchers [I] [2] [4] [6] [ll]
-
[13].Table 1 : Magnetic properties Fig. 1 : Magnetic field depend- for various grade sheets. ence on damping capacity for
various grade sheets at maximum strain amplitude o f 20x10-5.
In order to alter domain structures in the specimens, tensile stress was applied to the longitudinal direction of G-8. Fig.2 shows the effect of tensile stress on magnetic damping capacity AQ-: for the different maximum strain amplitudes. Magnetic damping was exponen- tially decreased with increasing tensile stress. Moreover, it was observed that the application o f tensile stress removes transverse domains in supplememtary structures such as lancet comb and lozenge structures, and simultaneously refines 180° domain wall spacing.
On the other hand, the correlation between the domain structures and magnetic core loss under tensile stress applied to the rolling direction has been so far studied by many investigators [18]-[20]. The changes of domain configuration observed here were the same as they have found, and also the reduction o f magnetic damping shown in Fig.2 was similiar to the curve on 180" wall spacing [20][21] and core loss under applied stress.
It should be attributed as the results that since the anomalous eddy current loss [22] is related to the refinement in 180' wall spacing occurring under applied tensile stress, the reduction of magnetic damping is due to the elimination of transverse domains.
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pickling in a diluted mixed solution of HF and HC
,
where care was taken to thinned as a flat plate as possible, and then annealed as early described and again the damping test was made in various stages to approximately 0.16 mm. Fig.3 shows thickness dependence of magne- tic damping capacity under different tensile stresses.6 - 8 0.30 mm. r h ~ c k -
-
- --
Fig. 2 : Effect of tensile stress on magnetic damping for different
I I I I I maximum strain amplitudes.
0 10 20 30 40 50
It is clearly seen from these results that magnetic damping capa- city in unstressed state exhibits a remarkable peak at 0.29 mm thick- ness, and such the peak is suppressed with increasing stress and
2
disappears at stress of about 30a40 Kg/cm
,
although the experimental values were appreciably scattered. Here the specimens of 0.30 mm thickness is being coated with the glass film and for 0.29 mm removed by the acid pickling. Such the fact means that a formation of the glass film on the specimen's surface reduces magnetic damping and2
corresponds to the tensile stress of 30%40 Kg/cm
.
This value is in good agreement with that determined from core loss in the specimens with and without coating under different stresses [23].thickness (mm)
Fig. 3 : Effect of thickness dependence on magnetic damping under different tensile
amplitude of 2 x l 0 - ~ . Here the abscissa represents the angle between a longitudinal axis of the specimen and the rolling direction. It can be seen from the figure that damping capacity is thc highest when is $=5S0 for the unstressed specimens and when is @=70° for the stressed ones. This means that the effect of tensile stress on damping capac- ity in the specimens with @<5S0 and Q>5S0 is entirely different from each othcr, that is, for 0<5S0 damping capacity decreases and for @>5S0 increases with increasing applied stress, whereas for 4=5S0 remains unchanged.
Such the changes by tensile stress were observed also for permea- bility. It was seen as the results that damping capacity corresponds to the magnetic softness as in the case of the random oriented sheets described previously. However, in the unstressed state, the opposite relation was found since the magnetic properties of Q=5S0 are the hardest among the all orientations. This will be discussed in terms of the bchavior of domain structures and magnetostriction in the specimens magnetized.
References
Fig. 4 : Orientation dependence on damping capacity under unstressed and stressed state.
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C5-620 JOURNAL DE PHYSIQUE
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