universiti putra malaysia establishment of...
TRANSCRIPT
UNIVERSITI PUTRA MALAYSIA
ESTABLISHMENT OF OPTIMUM PROCESSING CONDITIONS FOR SOME TECHNOLOGICAL MANGANESE-ZINC FERRITES
ROHAIDA TAMIN
FSAS 2002 4
ESTABLISHMENT OF OPTIMUM PROCESSING CONDITIONS FOR SOME TECHNOLOGICAL MANGANESE-ZINC FERRITES
By
ROHAIDA TAMIN
Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, In Fulfilment of the Requirements for the Degree of Master of Science
January 2002
Abstract of the thesis presented to the Senate ofUniversiti Putra Malaysia in fulfilment of requirement for the degree of Master of Science
ESTABLISHMENT OF OPTIMUM PROCESSING CONDITIONS FOR SOME TECHNOLOGICAL MANGANESE-ZINC FERRITES
By
ROHAIDA TAMIN
January 2002
Chairman Associate Professor Dr. Mansor Hashim
Faculty Science and Environmental Studies
This research work is an initial step to produce manganese-zinc ferrites in
the laboratory using the solid-state ceramic preparation method with controlled
atmospheres. The first part of the work was to develop the required material by
manipulation of composition. Then, the specimens were sintered at 1350°C in an
oxygen partial pressure. At this stage, a systematic crucial approach was used to
produce high permeability ferrites with suitable oxygen partial pressure. This
involved a gradual introduction of nitrogen gas into the furnace during sample
cooling giving an optimum equivalent isocompositional line. This work has
successfully produced materials (samples MRQI and MRQ2) suitable with the
permeability in the range of 2000 to 2500 when an average particle size was
reduced to �2.511m and zinc oxide was added to minimize zinc loss. Then the
sintering cycle was made to follow the isocompositional line.
ii
In conclusio� an optimum processing technique has been established for
producing ferrite materials with the desired magnetic properties.
iii
Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia bagi memenuhi keperluan ijazah Master Sains
PENGUJUDAN KEADAAN PEMPROSESAN YANG OPTIMA BAGI BEBERAPA BAHAN FERIT MANGAN-ZINK UNTUK KEGUNAAN
TEKNOLOGI
Oleh
ROBAIDA TAMIN
Januari 2002
Pengerusi Profesor Madya Dr. Mansor Hashim
Fakulti Sains dan Pengajian Alam Sekitar
Kerja penyelidikan ini adalah satu langkah awal untuk menghasilkan ferit
mangan-zink di dalam makmal dengan menggunakan kaedah penyediaan seramik
keadaan pepejal dengan atmosfera yang dikawal. Penyelidikan dimulakan dengan
menghasilkan bahan yang dikehendaki melalui manipulasi terhadap komposisi.
Seterusnya, pensinteran bahan spesimen pada suhu 1350°C di dalam tekanan separa
oksigen dilakukan. Pada peringkat ini, suatu pendekatan yang sistematik dan amat
perlu dilakukan supaya menghasilkan ferit dengan tekanan separa oksigen yang
sesuai. Ini melibatkan pemasukan beransur gas nitrogen ke dalam relau semasa
penyejukan sampel serta memberikan satu garisan isokomposisi setara yang
optima. Penyelidikan ini berjaya menghasilkan bahan (sampel MRQl dan MRQ2)
yang sesuai dengan julat ketelapan di antara 2000 ke 2500 apabila purata saiz zarah
iv
dikurangkan sehingga -2.5llm dan zink oksida ditambah untuk meminimakan
kehilangan zink. Kemudian, kitaran pensinteran dijalankan supaya mengikut
garisan isokomposisi tersebut.
Kesimpulannya, suatu teknik pemprosesan yang optima telah dapat
diujudkan untuk menghasilkan bahan ferit dengan sifat-sifat magnet yang
diperlukan.
v
ACKNOWLEDGEMENTS
I would like to extend my deepest gratitude and appreciation to my
supervisor, Associate Professor Dr. Mansor Hashim and my co-supervisors, Dr
Jamil Suradi and Dr Jumiah Hassan, for their invaluable guidance, advice and
constant support throughout the course of this research.
I am very grateful to all my dearest friends especially Kak Ana, Zolman and
Masdhiah for sharing their knowledge, advice and help towards the completion of
this research.
Finally, my dearest thanks to my family members for their encouragement
and most importantly to my husband for his support, care and understanding.
vi
I certify that Examination Committee met on 25th January 2002 to conduct the final examination of Rohaida Tamin, on her Master of Science thesis entitled "Establishment of Optimum Processing Conditions for Some Technological Manganese-zinc Ferrites" in accordance with Universiti Pertanian Malaysia (Higher Degree) Act 1980 and Universiti Pertanian Malaysia (Higher Degree) Regulation 1981. The Committee recommends that the candidate be awarded the relevant degree. Members of the Examination Committee are as follows:
ABDUL BALIM SAARI, Ph.D. Professor, Faculty of Science and Environmental Studies, University Putra Malaysia. (Chairman)
MANSOR HASHIM, Ph.D. Associate Professor, Faculty of Science and Environmental Studies, University Putra Malaysia. (Member)
JAMIL SURADI, Ph.D. Faculty of Science and Environmental Studies, University Putra Malaysia. (Member)
JUMIAH HASSSAN. Ph.D. Faculty of Science and Environmental Studies, University Putra Malaysia. (Member)
� � SHAMSHER MOHAMAD RAMADILI, Ph.D.
ProfessorlDeputy Dean School of Graduate Studies University Putra Malaysia.
Date:
Vll
This thesis submitted to the Senate of University Putra Malaysia has been accepted as fulfillment ofthe requirement for the degree of Master of Science.
VllI
AINI IDERIS, Ph.D. ProfessorlDean School of Graduate Studies University Putra Malaysia
Date: 09 MAY 2002
DECLARATION
. I hereby declare that the thesis is based on my original work except for quotation and citation, which have been duly acknowledged. I also declare that is has not been previously or concurrently submitted for any other degree at UPM or any other institutions.
Date: Iq (3(02
ix
TABLE OF CONTENTS
Page
ABSTRACT ............................................................................... 11
ABSTRAK................................................................................. IV ACKNOWLEDGEMENTS ..... , ... '" ., .......... '" '" ..... , ., .. , .......... '" ... .... VI
APPROV AL ... '" ....................... , ., ......... , .... ,. '" ..... , .... , . ... . . . ... ... ... .. Vll
DECLARATION.................................................................... ...... IX
LIST OF TABLES ........................................................................ Xlll
LIST OF FIGURES ................. , .. , ............................... ,. ... ... .. . ... . ... XIV
LIST OF PLATES ............ , .. , .............. , ........... , .... , . '" ... ... ... ... ... ...... XVll
LIST OF SYMBOLS & ABBREVIATIONS ... '" ... '" ... ...... ...... ... ... ... ..... XVlll
CHAPTER
I GE�RAL INTRODlJCTION ........... , ...... '" .. , .......................... . 1
Historical Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I Soft Magnetic Materials........................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 3 Objective of Work . .... . . . ... , . . . . . . . . . . . . '" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Evolution of Magnetic Properties ........... , '" ............... '" ........ , ., .. ,. 5
II LITERATURE REVIEW ................. . ...... '" . . . . . . . . . . . . . . . . . . . . . . . , . . , . , . 9
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Some Aspects of Manganese Zinc Ferrites... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 0 Microstruture Aspect of Manganese Zinc Ferrites............................ 11 The Effect of Grains Size on Permeability.................. ............... . . . . . 1 3 Exaggerated Grain Growth in F errites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
III SOME BASIC THEORY OF TECHNOLOGICAL FERRITES............ 1 8
Basic Concept of Ferrites .............. , ... ' " . . ........ , ......... . .... . .......... . Ionic Charge Balance and Crystal Structure ................
.................... .
Site Preference of the Ions ........................................................ . Interaction between Magnetic Moment on Lattice Sites ..................... . Magnetic Properties of Ferrites .................................................. . I . . P
. ntnnSlC ropertIes ................................................................. .
S . M . .
aturatlon agnetlZatlOn ............................................... .
x
1 8 1 9 2 1 22 23 24 24
Curie Temperature .. . .. . .. , ...... ...... ... ... ... ... ... ... ......... ....... 26 Magnetic Anisotropy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 26 MagnetostnctlOn . . . . . . . . , . . . . . , . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . '" . . . . 27
Extrinsic Properties................................................................. 28 Permeability ... . ..... . . . ... . ........ . . . . ........ . .. . . . . . ........... ....... , 28 The Hysteresis (B-H) Loop............................................. 32
IV mGH PERMEABILITY FERRITES... ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Introduction . . . . . ..... . .... . .. '" . . , . . . . . . " . '" . . . '" . . , '" . . . . . . . . . . . . . . . '" . . . . . . . . 36 Permeability Dependence on Chemistry ..... . .... . .... . .. '" '" . . , . . .. . , . . . . . . . 38 Effect of Iron Content on Permeability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Permeability Dependence on Zinc ........ , '" . . , '" . . . '" . .. . . . . . . . . . .. . . . , '" . . , 46 Oxygen Stoichiometry.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Effect of Purity on Permeability.......................................... . . . . . . . . 49
V FERRITES PROCESSING AND EXPERIMENTAL MEASUREMENT. 51
Introduction ......................................................................... . Laboratory Process ............................................................... ,. Raw Material Selection . . . . .. . . . . . . ................. . ... . ... . . ... . .... . . . . ..... . . . . Calculation of Weight and Weighing ........................................... . Mixing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Presintering ......................................................................... . Milling ..... , . . .. . ... . .... . , . , . .. , ' " . . .. . . . . . ... . ..... ' " ' " ' " . . . . .... . . .. . . . .... . . . Compact Forming ................................................................. . Sintering ... '" . . . ... . .. . . . .. , . , .. . . . , . . . , '" ' " .. . .. . . . .. . .. . . '" .. , . .. . .. . . , '" . . . . . . Sintering Cycle .................................................................... .
Heating Section . . . ..... . . .. . . . ... . . ...... . .. . . . .... . ... . . . ... . ... . . . . . . . . , High Heat Section ....................................................... , Cooling Section ............................................. : . . . .. . . . . ... ,
Experimental Measurement ...................................................... . Relative Initial Permeability ............................................ .
Hysteresis Parameter ................................................... . . Density ............... '" . . .. . .... . . ... , ...... . . . '" '" . ........ . . . '" ... .. . Resistivity ................................................................. .
Microstructure Analysis ................................................ . Cutting, Polishing, Etching and Microstructure Analysis .......... . Error Estimate ........................................................... .
xi
51 52 54 55 56 56 57 57 58 58 59 60 61 64 64 64 65 66 67 68 69
VI RESULTS AND DISCUSSION .... , . .. , . . , ..... . '" ....... ....... , .. , . .. ' " ..... 70
Development 1: Effect of Sintering Conditions on Permeability of Base 71 Sample-Mno.25Zno.2s(F �04)0 . 5 . . . . .. . . . . . . . . . . .. . ... . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . Development 2: Preparation and Properties of Fine Particle MnZn 78 Ferrites .............................................................................. . Development 3: Effect of Sintering Parameters on Zinc Loss for 85 Preparation of High Permeability Manganese-Zinc Ferrites ................. , Development 4: Magnetic, Electrical and Mechanical of Manganese- 90 Zinc Ferrites ........................... '" ... .. , .... . ......... .. , . . , ..... . , .. . ...... . Notes on Possible Application. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Comparison of Results with the Application Classification Data.. 96
VII CONCLUSION .............. , ............. , .. , .......... '" ....... , .. ,. ... ... .. . ... 98 Summary of Main Results ... '" . . . . . . '" . , . . , . . , . . . . . . . '" '" . . . '" '" . , . . . , . . . . . . 98 Final Remarks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
BmLIOGRAPHY.................................................................. 1 00 APPENDICES........................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . 1 04 VITA................................................................................. 1 13
xii
LIST OF TABLES
Table Page
1 Radii of Tetrahedral and Octahedral Sites in Some Ferrites...... 22
2 Saturation Magnetostrictions of Some Ferrites... ... ... ... . .. . .. ... 41
3 Error estimates for characteristics of the MnZn ferrite samples... 69
4 Density for Ultrafine Mno.2SZno.2S(Fe204)0.5. . . . . . . . . . . . . . . . . . . . . . . . . 83
5 Magnetic Properties ofMRQl and MRQ2 ..... , .,. '" .... ,. '" ...... 90
6 Resistivity ofMRQ1 and MRQ2 ........ , '" .. , ...... '" ... ... ... ..... 93
7 Comparison of Some Magnetic Properties for Samples Prepared 96 in This Work and Application Classification Data ................. ,
8 Data for samples Mno.2sZno.25(Fe204)O.5 with different sintering 110 conditions ................................................................ .
9 Data for Indutance, L and Permeability, II for ultrafine 111 Mno.25Zno.2s(Fe204)O.S after sintering using ultrafine ferrite powder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10 Data for Indutance, L and Permeability, II for x=0.01, 0.02 and 112
0. 03 of the ferrite Mno.2sZno.2S.x(Fe204)O.S+x .................................... ..
xiii
Figure
1
2
3
4
5
6
7
8
9
10
11
12
13
LIST OF FIGURES
Maximum permeability as a function of the year attained ................ .
Ma�imum �Q product as a function of the year attained ... ' " . . . . . , . . . . . .
Permeability of a MnZn ferrites as a function of grain size in microns ..
Permeability of high-permeability MnZn ferrites as a function of grain size ..................................................... , ' " . . , . . . . . . . . . . . . . . . . . . . . .
Crystal Lattice of Spinel Structure ...... ' " ' " . . . . . , . . . . . . ' " . . , . . . . . . . . . . . . . .
Effect of zinc substituition on the magnetic moments of some ferrites ..
Permeability spectrum plot of a nickel ferrites showing the frequency course of the real imaginary permeabilities ................................ .
Gradual change in direction of moments inside a domain wall (Bloch wall) ..... , . , . . . . . , . . . . ' " . . , . , . . . . . . . . . . . . . . . . . . . . . . ' " . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Magnetic induction B vs applied field H hysteresis loop for a ferromagnetic material. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Compositional dependence of crystal anisotropy and magnetostriction constant in the mixed oxide system (MnZnFe)-Fe204 .................... .
Constant permeability contours relative to zero crystal anisotropy K1, and Saturated magnetostriction for the (MnZnFe)-Fe204 system ....... . .
Variation of temperature dependencies of the permeability of some MnZn ferrites with composition. (a) 50.6% Fe203, 31% MnO. (b) 53.6% Fe203, 31% MnO. (c) 53.6% Fe203, 31% MnO. (d) 53.6% Fe20), 31% MnO ............ ' " . . . . . . .. . ' " . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Variation of permeability and magnetostriction as a function of F e203 content. ............. , ' " ' " ' " . . , ' " . . , . . . . . . ' " . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . .
xiv
Page
6
7
13
14
21
25
30
33
34
37
38
42
44
14 (a) Permeability ofMnZn ferrites as a function ofFe:z03 content. 45 (b) Variation of magnetostriction of the same MnZn ferrites as a function ofFe:z03 content. (c) Variation of permeability with magnetostriction for MnZn ferrites having the same composition but frred differently . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ,
15 Variation of permeability and crystal anisotropy constant, Kl, with 46 temperature in a MnZn ferrite containing 31 MnO- 11 ZnO-58 FezO) ...
16 Flow chart for sample preparation........................................ .... 54
17 Conceptual firing cycle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... 59
18 Equilibrium weight changes as oxygen as a function of atmospheric 62 oxygen content and temperature ............... .............................. .
19 The basic circuit configuration for hysteresis measurement............ ... 65
20 Density measurement set-up. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... 66
21 Illustration of a toroidal shape sample with metal-coated parallel 67 surface ... ' " . . . ' " .. . .. . . . , . .. ' " . . . ' " . , . . , . .... ... . . . . . ' " . . . . . . .... . . ' " ' " . . . .
22 Flow chart for microstructure measurement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... 68
23 Equilibrium weight change as oxygen as a function of atmospheric 73 oxygen content and temperature for the system: (MnO)O.Z68(ZnO)O.183(Fez03)0.549 (after Slick 1971) ................. ..... .
24 Inductance, L for four samples ofMno.zsZno.zs(Fez04)o.s vs Frequency 74 (kHz) with Different Sintering Conditions ...................................... ......... .
25 Initial Permeability, J..l. for four samples ofMno.zsZno.zs(Fez04)O.5 vs 75 Frequency (kHz) with Different Sintering Conditions ......................................... .
26 Quality Factor, Q for four samples ofMno.zsZno.zs(Fez04)o.s vs 77 Frequency (kHz) with Different Sintering Conditions . .............................................. .
27 Relative Loss Factor, RLF for four samples ofMno.2sZno.zs(Fez04)o.s 78 vs Frequency (kHz) with Different Sintering Conditions .................................. .
xv
28 The average particle diameter distribution for ultrafine 80
�.2SZno.2S(F e204)0.5 . . . . . . .. . . . . . . ... . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . .. . . .. . .. . . . . . .. . . . . . . . . . . .. . . . . . . . . ..
29 Inductance, L vs Frequency for two samples ofmtrafine 8 1 Mno.2sZno.2s(Fe204)o.s After Sintering Using mtrafine Ferrite Powder ............... .....................
30 Initial Permeability, Il vs Frequency for two samples ofUltrafine 82 Mno.2sZno.2s(Fe204)O.5 After Sintering Using mtrafine Ferrite Powder ..
3 1 Inductance, L vs Frequency (kHz) for x=O.Ol, 0.02 and 0.03 of the 86 ferrite Mno.2sZno.2s-x(F e204)O.5+x . .. . . . .. . .. ....... . . . .. . .. . . ... .. .. . . .. . . . .....
3 2 Initial Permeability, Il vs Frequency (kHz) for x=O.OI, 0.02 and 0.03 87 of the ferrite Mno.25Zno.25-x(Fe204)O.5+x ......... ............... ... ... .........
33 Relative Loss Factor, RLF for samples MRQ1 and MRQ2 versus 92 Frequency ....
Al The basic configuration used to measure Bs, Br and He ................... 105
xvi
LIST OF PLATES
Plate Page
1 Scanning Electron Micrograph (SEM) ofMnZn Ferrite... . .. ..... 84
2 Microstructure of sample MRQ 1 with magnification x2000. . . . . . 94
3 Microstructure of sample MRQ2 with magnification x2000...... 95
xvii
LIST OF SYMBOLS AND ABBREVIATIONS
J.!j initial permeability
Q quality Factor
TC Temperature coefficient
D disaccommodation
Ms Saturation magnetization
MA Saturation magnetic moment for A site
MB Saturation magnetic moment for B site
B Induction
H Applied field
J.!o Magnetic constant
t Thickness
Do Outer diameter
Di Inner diameter
N Number of wire tum
L Inductance
J.!' Real part of permeability or magnetic loss
J.!" Imaginary part of permeability or magnetic loss
xviii
fr Loss resonance frequency
y Gyromagnetic ratio
Tan 0 Loss tangent
RLF Relative Loss Factor
J..lm Maximum permeability
Bs Saturated induction
Br Remanence induction
He Coercive force
Kl Crystal anysotropy
IlR Intrinsic rotational permeability
Il w Wall permeability
(j Internal stress
IlB Bohr magneton
PZn Pressure of zinc
Hmax Magnetic field for effective saturated induction
xix
CHAPTER I
GENERAL INTRODUCTION
Historical Overview
Magnetite or ferrous ferrite (Fe204) is an example of a naturally occurring
ferrite. It has been known since more than 2000 years ago and its weak permanent
magnetism found application in the compass of the early navigators. Nevertheless,
there was hardly any progress in scientific research concerning ferrites until the 19th
century (Ishino, 1987). Ferrite carne into prominence only at the end of the Second
World War (Goldman, 1990).
1
In an early work in 1909, Hilpert published the first systematic study of the
relation between the chemical and magnetic properties of a number of the binary
iron oxides but experienced difficulty in identifying the magnetic phase of his
preparation. He claimed that ferrites had caused high-energy loss when subjected
to alternating magnetic fields and thus had no commercial values. Around 1928
Forestier in France and Hilpert and Wille in Germany made quantitative
investigations into the relation between the chemical composition, the saturation
magnetization and the Curie temperature.
Japanese workers between 1932 and 1935 also studied magnetic oxides.
Practical utilization of the ferrites began after the research of Kato and Takei. In
1936, Snoek was studying magnetic oxides in the Netherlands. Snoek and his co
worker, Six, realized that the most important property of a material intended as a
core for an inductor is the loss tangent divided by the permeability, the so-called
loss factor. This is because the loss can always be reduced by the introduction of
an air gap provided the resultant permeability remains sufficient. This led Snoek to
the development of manganese-zinc-ferrous ferrite in which low loss and high
permeability were combined by minimizing the magnetocrystalline anisotropy and
the magnetostriction. By 1945 Snoek had laid the foundations of the physics and
technology of practical ferrites and a new industry came into being. Another
important discovery concerning ferrites was given by Nee! 1948, in the theory of
ferrimagnetism, which brought about a great advance in the magnetic investigation
of ferrites.
2
The large-scale introduction of the television in the 1950s was a major
opportunity for the new ferrite industry. Ferrite cores were the material of choice
in television sets for the high-voltage transformer and the picture-tube deflection
system. In the 1970s, ferrite cores were used widely in telecommunication and
electronic equipment such as mainframe computer memories, recording heads, etc.
(Hirota et aI., 1980). Since the early 1980s, ferrite cores have been used in high
frequency power supplies (Roess, 1982; Bracke, 1983).
Soft Magnetic Materials
Soft ferromagnetic or ferrimagnetic materials are those which have been
developed with technical applications in view, to allow changes in magnetization to
occur easily in weak magnetic fields. When the applied fields is removed, they
return to a state of relatively low residual magnetism. Important magnetic
properties of a soft magnetic material are high permeability, high saturation
induction and . low coercive force. The converse, the need for high magnetizing
field and high remnant magnetism is true for hard magnetic materials.
F errites may be defined as magnetic materials composed of oxide
containing ferric ions as the main constituent. They are hard, brittle, ceramic-like
materials and are classified as ferrimagnetics. Ferrites are polycrystalline and are
3
generally dark grey or black in appearance. Ferrites have three distinct crystal
structures: The hexagonal magnetoplumbite, dodecahedral garnet and the spinel
structure (Crangle, 1991; Standley, 1972). The first structure is that of hard
ferrites, the later two being those of soft ferrites.
Some of the applications for soft ferrites are for low signal, memory-core,
audio-visual, and recording head applications. At low signal levels, soft ferrite
cores are used for transformers and low-energy inductors. A large tonnage usage of
soft ferrites is for deflection-yoke cores, flyback transformers, and convergence
coils for television receivers. For these materials their survival in the intense
competition from the growing technologies and their ability to enter newer areas of
applications have promoted them to many disciplines. Consequently, the growing
information-oriented society and the expanding roles of ferrites in electronic
gadgets and other industrial pursuits have, in return, motivated this study.
Objective of Work
Besides Nickel-Zinc (NiZn) ferrites, Manganese-Zinc (MnZn) ferrites are
well known as a class of ferrites showing good soft magnetic properties up to the
MHz frequency range because of their high magnetic permeability and low electric
losses. The development and the continued success of electronics industry have
created an expanding commercial market. This market is continually challenging
4
the ferrite industry to produce high-quality ferrite cores capable of operating in
increasingly higher frequency. MnZn ferrite is the most important ferrites for such
application and constitutes a substantial portion of present-day soft ferrite
production.
This project may be considered as a basic research in processing and
preparation method of MnZn ferrite. Further research can be done to improve the
magnetic permeability of certain composition of MnZn ferrite due to the general
formula MnxZIl(1-x)Fez04 in order to produce better properties close to commercial
specifications.
The objective of this project is to prepare the MnZn ferrites with high initial
permeabilities in the range of 2000 to 5000 which are now commercially available,
with the higher permeabilities limited to small toroids. Attaining such high
permeabilities on a commercial scale has been a technological challenge. As such,
this experiment at work can lead to the beginning of important efforts at UPM to
attain high permeability soft magnetic materials, starting with MnZn ferrites.
Evolution of Magnetic Properties
Figure 1 and 2 have shown the values of maximum permeability and �Q
product as a function of the year that the values were attained (Slick, 1980). This
5