The effect of magnesium oxide coating oh the magnetic properties of non-magnetostrictive amorphous Co70.4Fe4.6Si15B10 alloy

~~t~r~~ls C~e~isfry and Physics, 15 f 1986) 45 l-456

451

SHORT CO.~UNICATION

TRE EFFECT OF MAGNESIUM OXIDE COATING ON THE MAGNETIC PROPERTlE8 OF NON-MAGNETOSTRICTIVEAMORPBOU8 Co70.4F~4.6+~,o AUCI

J. MEHLIS, and A. ZWADA

Institute of Ferrous Metallurgy, Miarki 12, 44-100 GLiwice

(Poland)

Institute of Physics,,Technical University, Al. Zawadzkiego 19, 42-200 Csqstochowa (Poland) Received May 2, 1986; accepted June 3, 1986

ABSTRACT

The influence of a surface coating of magnesium oxide on the magnetic properties of toroids made of non-magnetoetrictiveamorphOU8 CO+70 Fe4 (.jSi B 0 alloy hss been investigated under sinusoidal induct4 ons'up i2 d .8T in the frequency range from 400%~ to 10 kRe. The most important effects of the coating are the decrease of of maximum perpower losses and coercive force, and the increase meability.

INTRODUCTION The state of the s.urfaceof ferromagneticmaterial affects the distributionof dislocations snd thus the physico-chemicalproperties of these materials. However, free and non-free surfaces affect the propertie%

of

ferromagnetic

material

in different

ways.

In the

ca%e of the lack of coating on the surface of ferromagneticmaterisl, i,_e,in the case of free surface, the dislocations are attracted

to the specimen

coating

and of

between

the

over

short

surface,

When the Young’s

the ferromagnetic

surface

coating

material

of

the surface

have similar

values

then

repulsion

force8

occur

and dislocation%

distances, whereas over long distances attraction forces

[l]. Keeping in mind the above to investigate

the selection

of

observations, chemical

ment of

such method% of surface

coating

tageoua

effect%

properties

The effect 012%ribbon

moduli

on the magnetic of

the coating

has 80 far

0254-0584/86/$3.50

been

it

deposition of

on the magnetic investigated

seems interesting

compo%ition

by

and developto obtain

advan-

the amorphous

ribbons.

properties

of

amorph-

p-43 but the data obta-

0 Elsevier Sequoia/Printed inThe Netherlands

452

ined are not univocal. Price et al. [2] observed that the power loss and the msximum permeability of the amorphous Fe8,B,5 5Si3.5C2 alloy subjected to heating were independent of the MgO suriace layer or water solution of resin. On the other hand Nathasing et al. [3] have shown that the incressed losses associated with a smooth tension wound Fe78B19Si9 amorphous ribbon can be eliminated by using a coating of colloidal or powdered silicon dioxide. Distinct reductions of power losses and coercive force of ribbons made of amorphous Fe82B,2Si6, Co70Fe5B,8Si7and Fe40B20Ni40 alloys due to the influence of the surface coating produced by phosphatizing in aqueous solution of H3P04, Mg(H2P04)2 and A1(H2P04)3 have been observed [4]. The present investigationwas intended to determine the effect of a magnesium oxide coating on the magnetic properties of non-magnetostrictive amorphous c07~.4Fe4.6Si,5B,0 alloy. EXPERIMENTAL PROCEDURE The amorphous ribbon used in this study was prepared by a single -roller quenching technique. The ribbon obtained was s. 40 nm thick and 10 mm wide. In order to produce the coating, magnesium oxide of composition (wt$): MgO-97.50, CaO-0.8, Fe203-0.20, A12030.42, Si02-1.5, B202-0.015, C-O.024 dissolved in carbon tetrachloride with addition of oleic acid was used. Directly before the preparation (not earlier than 12 h) the magnesium oxide was roasted for 5 hrs at550 'C. The surface coating on amorphous ribbons was produced by means of sn electrophoresismethod in a device supplied with the toiler of toroidal coxes. In this device the amorphous ribbon passed SUCcesaively through degreasing tanks containing degreased petrol and a suspension containing magnesium oxide. The negative pole of the d.c. source was connected to the ribbon and the positive pole to the tank and electrodes. In the electric field, on the surface of the metallic glass a thin coating of magnesium oxide was deposited. The thickness of the coating was controlled by the applied voltage and the ribbon coiling rate. The MgO coating, just after deposition on the ribbon surface, is non-resistant to abrasion and was dried at 60 'C. The measurements of the magnetic properties were made with the use of toroidal specimens coiled from the ribbons with and without coating of pack factor 87 % and 83 $6,respectively,heated in a ni-

453

trogen atmosphere at 430 'C for 15 min. Core losses and permeabilities of amorphous ribbon toroids have been measured under sinusoidal induction conditions up to 0.8 T over a frequency range from 400 Hz to 10 kHz with the accuracy about 1 %. To avoid any external winding stresses in the materials the toroids were contained in enclosed formers and the coils wound around the formers.

RESULTS AND DISCUSSION The microstructure observed on the cross section of amorphous ribbon coated with MgO layer is presented in Fig. 1. It is seen that the coating is uniformly produced on the ribbon surface and its thickness is a. 1 pm.

Fig. 1. Microstructure of amorphous Co70 with magnesium oxide coating after anneal a - white light, b - polarized light. The results obtained for power loss (P) and maximum permeability (pm,) frequency for toroids treated with and without the coatings show a beneficial effect on the properties of the toroide within the measured frequency range, 400 Hz to 10 kHz, and the induction range up to 0.8 T (see Fig. 2). The MgO coating produces not only the decrease of P and the increase of nmmax but it also produces the decrease of the coercive force (AC) within the whole tested range frequency (see Fig. 3). The improvement of magnetic properties of the amorphous Co7o 4Fe4 $i15BI0 ribbons observed in this work can be explained if ine ass&es that the surface of the ribbons coated with MgO contains muc

454

0,3T.

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’ ’

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2, E&mom permeability ( vs. frequency at different ted (- - - ) and uncoated (-1 alloy core%.

I

I

n’ ’

f[Hzl

‘(I4

) vs. frequency and power loss tions for rna~es~~ oxode coaamorphous Co70 4"e4 6'3 2%0 . l

fewer defects compared with the ribbons without this coating and that the domain walls during magnetization are pinned only at the ribbon surface. The coercive force generated is the result of the losses of energy required to separate the domains walls from surface defects and can be described by the following equation [5]:

where S is a dimensionlese constant that describes the details of surface roughness, A is the exchange constant, K is the anieotropy

IO340' I -I

I

I

Illll

IO”

I

I

I

Illll

-I

I

-

f [Hz]

IO'

Fig. 3. Coercive force vs. frequency for magnesium oxide coated amorphous Co70 4Fe4 6si12B10 a11oy (- - -) and uncoated (-) . . cores.

constant, MS is the saturation magnetization and d is the ribbon thickness. The decrease of the coercive force observed in this work on toroids coiled from the ribbons coated with MgO can then result from elimination of surface defects. One can also expect that the magnesium oxide coating deposited on the surface of amorphous C"70.4Pe4.6Si12B10alloy does not induce these stresses in the ribbons which cause the changes of domain structure and consequently the changes of magnetic properties, similarly to the case of grainoriented Fe-3wt% Si alloy PI. ACKNOWLETICMEXPS This work has been subsidized by the Institute of Materials Science and Engineering, Warsaw Technical University, Warsaw.

Zh, Fridel, Dislokacja, Mfr, Moskva, 1967. H.J. Price, M.H. Price and K.J. Overshot& IEEE Trans, MaRn., MAC-19 (1983) 1943. D.M. Nathasingh, C.H. Smith and A. Datta, IXEE Trans. Mawl., MAG20 (1984) 1332. A. Zentko, A. Knsturiak and P. Duhaj, IEEE Trans. M&w&, NAG-20 (1984) 1326. E,M. Gyorgy, in J.J. Gilmsn and H.J. Lemay (eds), Metallic Glasseg, American Society for bfetals,Ohio, 1978. G,A, Braschevan, L.F. Antonova and H,T. Andrianov, Trudy Instituta Fiziki Metaflov, Akad. Nauk SSSR-Uralskiy Nauchniy Centr, t1977) 123 l