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On the origin of core losses in a manganese zinc ferrite with appreciable silica content

G. C. Jain, B. K. Das, and Santosh Kumari

Citation: Journal of Applied Physics 49, 2894 (1978); doi: 10.1063/1.325173

View online: http://dx.doi.org/10.1063/1.325173

View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/49/5?ver=pdfcov

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nthe origin of core losses

in

a manganese zinc ferrite

with appreciable silica content

G C

Jain, B K. Das, and Santosh Kumari

Division o Materials. National Physical Laboratory. New Delhi 110012. Ind ia

(Received 25 March 1977; accepted for publication

10

June 1977)

The effect

of

silica on the magnetic properties and microstructure of a manganese zinc ferrite has been

studied. It is found that as silica content increases. the magnetic properties

at

first improve. then

deteriorate around 0.04% silica due to discontinuous grain growth. At still higher silica contents.

magnetic properties deteriorate further due to an increase in the total effective magnetic anisotropy.

PACS numbers: 75.50.0g, 81.40.Rs, 75.60.Ej

I. INTRODUCTION

Silica is

the main impurity in most of the raw

mate

rials used in the preparation of ferrites, especially

ferric oxide, and it is known to affect the various

magnetic properties of Mn- Zn

fer rites

significantly.

I t has therefore become necessary to understand the

effect of the

silica

content in Mn- Zn

ferrites

in order

to

prepare

ferrites with

reasonable properties

using

comparatively

impure

raw

materials.

Manyauthors

t -

3

have studied the effect of small additions of Si 0

2

on the

microstructure and the low-field properties of ferrites.

The present work

deals

with a study of power

losses

at high flux densities and microstructure with different

Si0

2

contents. This owes

its

importance

in developing

a Mn- Zn ferrite with low

core

losses for high-frequency

power application using raw

materials

containing

ap

preciable silica.

II. EXPERIMENTAL METHODS

Mn-Zn ferrite of basic formula

M l l o 5 6 4 Z l l o 3 7 4 F ~ o 6 0 4

was prepared to which various amounts of

silica

ranging

from O.

01

to

0.64%

(all

silica

percentages

are

weight

percents) were added using usual ceramic techniques.

Initial raw

materials

contained

less

than

O. 01

%

silica.

The

toroids pressed

out of these. were fired in a pure

nitrogen atmosphere at 1275 C for

45

min and cooled

in

pure

nitrogen.

3000

t

~ 2 5 0 0

::::i

iii

~ 2 0 0 0

::IE

a:

w

Q,

1500

...J

c

i=

1000

Mn

O

IM

Zn

O174

Fe;&O.0

4

12nSC/45mln. N

z

Core Ios.e. /

/

- - - - ~

'

.. '

....... , '

--

-----

SiO

z

CONTENT IN

W T . ~ -

'

/

I

/

/

FIG. 1. Initial

permeability

and core losses

at

2000 G

and

15.75

kHz

vs

silica

content.

Power-loss measurements

were

taken on

toroids

(0. d. =::

1.

36 cm,

i.

d. =:: 0.84 cm, and thickness =:: 0.21

cm) at a peak flux density of 2000 G and up to a fre

quency of 15.75 kHz. An

incremental

inductance

bridge

type 1633-A with an inductance-measuring assembly

type 1630-AV (General Radio Company,

USA

was used

for

this purpose.

Hysteresis curves

were

also

pictured

under the

same

conditions on a loop

tracer.

Microstructures

of

these

samples were

observed

after etching the

metallographically

polished

specimen

in a 3 : 1 solution of hydrochloric acid in ethyl alcohol.

In order to locate the

silica

distribution a scanning

electron microscope in

its

x-ray mode was used.

III.

RESULTS

A. Magnetic properties

Figure 1 gives the

initial permeability

III and power

loss density as a function of Si0

2

addition.

IJ.j

at first

increases with silica content up to 0.02%, falls off and

remains constant up to

o

16%

Si0

2

, and then

drops

further at the two highest

silica

contents. At 15.75

kHz,

power-loss

density shows a peak

at

the

silica

content of 0.04% and then a rise at the two highest

silica contents. Figure 2

gives

power-loss denSity/kHz

for

different

frequencies.

Intermediate levels of silica

N

J:

>

e'

( )'"

'

::E

K

500

200

400

0

01 '02

04

08

'16

32

64

i 02

content in wt

FIG.

8.

Ms.

K. and

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total

effective anisotropy causes the

slanting

of the

B-H

loop and therefore the

increase in

the

losses.

In order to explain the

behaviour

of initial permeabil

ity,

the product MsD/K1 2,

where

D, is the

average

intragranular pore-to-pore distance

or the grain

diam

eter,

whichever

is

smaller, is

plotted

against the silica

content Fig. 8 and

it

can

be seen that the behavior

is

similar to that of IJ.j. Globus

12

and

Das

and

Chaudhari

t3

have shown that the domain

wall

contribution

to

I l i

is

given by

I l i

-

1 M Dh,

where

y is the domain

wall

energy

[=

(AK)t ] and A

is

the exchange constant - M;

I t means that in

these

ferrites the initial

permeability

is dominated by the contribution due to the domain wall

bulging.

CKNOWLEDGMENTS

The

authors

wish to express their appreciation to

Dr.

A. Hepworth of Indian Institute of Technology,

Delhi,

for

the scanning

electron

microscope analysis

and

Dr.

S.

P. Bhattacharjee for

h l p ~ u l

discussions.

2897 J. Appl. Phys., Vol. 49,

No.5

May 1978

They also thank Dr. A. R. Verma, Director, National

Physical Laboratory, for granting

the permission to

publish this

work.

IT.

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Trans. Jpn.

Inst.

Met. 2, 171

1961).

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F.

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Knowles, and P.

Rankin,

Ferrites: Proc. Int. Conf. ,

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1970, p. 194 unpublished).

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Giles and

F.F.

Westendorp, J . Phys. to be

published).

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in

Ref. 3, p.

137.

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Ceram.

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Stuijts, Sci. Ceram. 8

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1975).

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J .

Mater.

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Dillon,

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et

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2897

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