1. Material Science Magnetic(자기적성질) Associate Professor Su-Jin Kim
School of Mechanical Engineering
Gyeongsang National University 1

2. OCW
Magnetic Permeability
Magnetic Properties
[Poor]
Gravitational Electric Magnetic Fields
Curie point demo

3. OCW
Ferromagnetic Paramagnetic Diamagnetic Magnetic logic Hard disk drive Induction motor

4. KOCW 재료의 자기적 성질1 재료의 자기적 성질2
재료의 자기적 성질2

5. Magnetic induction(자기유도)
Magnetic field(자기장) is created by current passing through a coil.
Magnetic induction(자기유도) occurs when a material is subjected to a magnetic field. It is a change in magnetic moment from electrons.
Magnetic field H
Current I
Magnetic induction B
Magnetic induction:
-- occurs when a material is subjected to a magnetic field.
-- is a change in magnetic moment from electrons.

6. 3 Types of Magnetism Types of material response to a field are:
Ferrimagnetic (Ferromagnetic)(강자성) : large magnetic induction, Magnetite(자철광 Fe3O4), NiFe2O4, Fe, Co, Ni, Gd
Paramagnetic (상자성): poor magnetic induction, Al, Cr, Mo, Na, Ti, Zr
Diamagnetic (반자성): small opposing magnetic moment, Al2O3, Cu, Au, Si, Ag, Zn
• Types of material response to a field are:
-- ferri- or ferro-magnetic (large magnetic induction)
-- paramagnetic (poor magnetic induction)
-- diamagnetic (opposing magnetic moment)
ferromagnetic paramagnetic diamagnetic

7. Magnet (자성체) Hard Magnet(경자성체) large coercivity good for perm magnets
add particles/voids to make domain walls hard to move
(e.g., tungsten steel)
Soft Magnets(연자성체)
small coercivity, good for electric motors
(e.g., commercial iron Fe) B
Applied magnetic field H
Flux density
Ferrite (magnet)
Ferrites are chemical compounds consisting of ceramic materials with iron(III) oxide (Fe2O3) as their principal component.[1] Many of them are magnetic materials and they are used to make permanent magnets, ferrite cores for transformers, and in various other applications.
Ferrites are usually non-conductive ferrimagnetic ceramic compounds derived from iron oxides such as hematite (Fe2O3) or magnetite (Fe3O4) as well as oxides of other metals. Ferrites are, like most other ceramics, hard and brittle. In terms of their magnetic properties, the different ferrites are often classified as "soft" or "hard", which refers to their low or high magnetic coercivity.
Soft ferrites
Ferrites that are used in transformer or electromagnetic cores contain nickel, zinc, and/or manganese compounds. They have a low coercivity and are called soft ferrites. The low coercivity means the material's magnetization can easily reverse direction without dissipating much energy (hysteresis losses), while the material's high resistivity prevents eddy currents in the core, another source of energy loss. Because of their comparatively low losses at high frequencies, they are extensively used in the cores of RF transformers and inductors in applications such as switched-mode power supplies.
The most common soft ferrites are:
Manganese-zinc ferrite (MnZn, with the formula MnaZn(1-a)Fe2O4). MnZn have higher permeability and saturation induction than NiZn.
Nickel-zinc ferrite (NiZn, with the formula NiaZn(1-a)Fe2O4). NiZn ferrites exhibit higher resistivity than MnZn, and are therefore more suitable for frequencies above 1 MHz.
Hard ferrites
In contrast, permanent ferrite magnets are made of hard ferrites, which have a high coercivity and high remanence after magnetization. These are composed of iron oxide and barium or strontium carbonate. The high coercivity means the materials are very resistant to becoming demagnetized, an essential characteristic for a permanent magnet. They also 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 cheap, and are widely used in household products such as refrigerator magnets. The maximum magnetic field B is about 0.35 tesla and the magnetic field strength H is about 30 to 160 kiloampere turns per meter (400 to 2000 oersteds).[3] The density of ferrite magnets is about 5g/cm3.
The most common hard ferrites are:
Strontium ferrite, SrFe12O19 (SrO·6Fe2O3), a common material for permanent magnet applications.
Barium ferrite, BaFe12O19 (BaO·6Fe2O3), a common material for permanent magnet applications. Barium ferrites are robust ceramics that are generally stable to moisture and corrosion-resistant. They are used in e.g. subwoofer magnets and as a medium for magnetic recording, e.g. on magnetic stripe cards.
Cobalt ferrite, CoFe2O4 (CoO·Fe2O3), used in some media for magnetic recording.[4]
Magnetic Logic

8. Magnetic Storage Tape or Card - particulate g-Fe2O3 in polymeric film
A hard disk drive (HDD) is a data storage device using rapidly rotating discs coated with magnetic material - thin film CoPtCr or CoCrTa on glass disk
Magnetic storage media:
-- particulate g-Fe2O3 in polymeric film (tape or floppy)
-- thin film CoPtCr or CoCrTa on glass disk (hard drive)
A hard disk drive (HDD) is a data storage device used for storing and retrieving digital information using rapidly rotating discs (platters) coated with magnetic material. An HDD retains its data even when powered off. Data is read in a random-access manner, meaning individual blocks of data can be stored or retrieved in any order rather than just sequentially. An HDD consists of one or more rigid ("hard") rapidly rotating discs (platters) with magnetic heads arranged on a moving actuator arm to read and write data to the surfaces.
Hard disk drive

9. Electric Transformer (변압기)

10. Electric Motor
The interaction between an electric motor's magnetic field and winding currents generates force
The interaction between an electric motor's magnetic field and winding currents generates force
Induction motor