magnetic & di-electric properties of ceramics_simple

8/14/2019 Magnetic & Di-electric Properties of Ceramics_simple

1/13

MAGNETIC & DI-ELECTRIC

PROPERTIES OF CERAMICS

Introduction

Importance

Origin of magnetism

Structures

properties Classification

Specific application

Manufacturers

Contents


2/13

WHAT IS (Magnetic Ceramics) FERRITE ?

Ceramic magnets containing iron as a major constituent.

Ferrites are a class of chemical compoundswith the formula AB

2O

4, where A and B

represent various metal cations, usuallyincluding iron. These ceramic materials areused in applications ranging from magneticcomponents in microelectronics.

Why should be Ferrite?

High intrinsic resistivity.


3/13

The intrinsic magnetic properties of a material are

determined by the electronic structure & the crystal

structure

According to Paulis Exclusion principle, only twoelectrons can occupy a given energy level and these two

electrons must have opposite spins.

A net magnetic moment occurs only when electron

energy levels are half filled, such as in the transition

elements, rare earth elements.

Orbital Magnetic Movement

( -1 Bohr Magnetron)

Spin Magnetic Movement

= proton

= neutron

=electron


4/13

Fundamental Concept

-Origin of Magnetism


5/13

Ferrite composition and structure

Cubic ferrites

Spinel General structure MFe2O4, where Fe is trivalent

and M is divalent Ni, Mn, Mg, Zn, Cu, Co, or a mixture

Garnet General structure R3Fe5O12, where Fe is trivalent

and R is a trivalent rare earth, typically Y or Gd.

Hexagonal ferrites

Various Structures BaFe12O9, Ba2MFe12O22,

BaM2Fe16O27

Ba3M2Fe24O41, Ba2M2Fe28O46Ba4M2Fe36O60, where M is

divalent

Ni,Co,Zn or Mg, and Ba can be

replaced by Sr and Pb.


6/13

Orthorhombic ferrites

Pervoskite General structure RFeO3, where R is trivalent

rare earth and Fe is trivalent and can be

partially replaced by trivalent Ni, Mn, Cr, CoAl, Ca or V5+

1. 8/64 Tetrahedral sites

2. 6/32 Octahedral sites3. MeOFe2O3 (Me: a divalent ion)

4. Mn2+, Fe2+, Co2+Ni2+, Cu2+, zn2+


7/13

Property of Spinel Ferrites

A. Low magnetic anisotropic

Magnetically soft

Exception: Containing Co2+

-> Very high Coercivity(-Hc).

Garnets: model Y3Fe5O12(YIG)

A. Group of iso structuralminerals with the general

composition (3RO-R2O3-3SiO2)

B. YIG ( Yttrium iron garnet ) : Ferrimagnetic-> Microwave material

C. Large cubic unit cell (a=1200pm)

containing 160 atoms


8/13

< Magnetic Hysteresis >

Soft-Hard Ferrite

Soft ferrites

Ferrites that are used in transformer orelectromagnetic cores contain nickel,zinc, or manganese compounds. Theyhave a low coercivity and are called softferrites. Because of their comparativelylow losses at high frequencies, they are

extensively used in the cores of Switched-Mode Power Supply (SMPS) and RFtransformers and inductors. A commonferrite, abbreviated "MnZn," is composed ofthe oxides of manganese and zinc.


9/13

Hard ferrites

In contrast, permanent ferrite magnets (or "hard ferrites"), which have a

high remanence after magnetization, are composed of iron and barium or

strontium oxides. In a magnetically saturated state they conduct magnetic

flux well and have a high magnetic permeability. This enables these so-called ceramic magnets to store stronger magnetic fields than iron itself.

They are the most commonly used magnets in radios. The maximum

magnetic field B is about 0.35 tesla and the magnetic field strength H is

about 30 to 160 kilo ampere turns per meter (400 to 2000 oersteds). (Hill

2006)Application

1. Transformer for Power application

-For Loss minimum.

2. Antenna

-For small size.

3. Ferrite Core Memory

-Highly stable & Storage Capacity

4. Magnetic Memory

5. Microwave Devices


10/13

1. Saturation Magnetization Ferrite: about 0.5(T)Si-Fe : about 2.0(T)

2. Higher Frequencies, Critical Eddy Current Losses. Metallic ferromagnetism

impossible.

3. Typically 1kHz1MHz

Transformer for Power application

Transformer for Power application

-Materials

1. Important to keep Low Crystalline Anisotropic

-> Substituting cobalt for about 1% of Nickel in (Ni,Zn)Ferrite.

2. NiZn Ferrites: up to approximately 5MHz MnZnFerrites: about 100kHz

-> High Permeabilities


11/13

Antennas

1. Small size radio receivers need Small Antennas.

2. We can make Small Antennas with Ferrites!!

Ferrite Core Memory

1. Br represent the digits 0 and 1.

2. Greater than HC field, switch to the

opposite sense.


12/13

Ferrite Core Memory

-Materials

1. Core Composition: Based on (Mg, Mn, Zn) Fe2O4

2. For a wider operating temperature range,(Ci, Mn) Fe2O4Li1/2Fe1/2Fe2O4

Microwave Devices

-Materials

1. Magnesium Ferrites

-about 200-40kA/m

2. Lithium Ferrites (Spinel Family)

-about 380-32kA/m

-High Curie Temperature up to about 670

-Superior for most situation.


13/13

Manufacturers

TI-Electronic

Acme-Ferrite

TDK

Strontium Ferriten India Limited

Dielectric Properties

Capability of the material to withstand andelectric field without breaking down andhas units of volts per unit of thickness ofthe dielectric material.Ex: Titanates, 100 to 300 V/mil

Micas, 125 to 5500 V/milPhenolics, 2000 V/mil.

Applications

Fabrication of capacitorsBaTiO3 - make possible substantialminiaturization of capacitors.

magnetic & di-electric properties of ceramics_simple

Documents