Chapter 1. Definition & unit

1. Introduction

2. Magnetic pole

3. Magnetization

4. Magnetic induction

5. SI unit

6. Kinds of magnetism

7. Unit conversion

국제단위계 (SI):

7개의 기본 단위 탄생 (1971년)

Unit system

-Not italic

(cf, equation is italic)

-Capital letter, small letter are different.

-Space between number and unit

Example for wrong expression

-Weight : 100 KG 100 Kelvin-giga

-Speed : 120 KM/H 100 Kelvin-Mega / Henry

-Frequency : 975 KHz 975 Kelvin-Hertz

-Length : 2 MM 2 mega-mega

1.1 Introduction

• History : Magnetite

Gilbert : Magnetite, 1600

Oersted : Current-magnetic field, 1820

Coulomb : Magnetic force between N-S poles, 1785

Ewing – Hysteresis loop, 1880, (M.)

Faraday : Magnetic induction, 1852

Maxwell – Electromagnetic wave, 1873

• Theory (Beginning of 20 C)

Curie – Temperature effect,

Langevin, Weiss, Ennl -

• Applications

Transformer – 1900, Permalloy – 1915

Alnico – 1931, Ferrite – 1940

Amorphous – 1980 High Tc SC – 1986

Magnetoresistance - 1988

Prof. Lebedev

[皇帝]

황제(黃帝)

(BC 2500)

• Force : Caused by magnetic poles at end, P (Coulomb’s law)

221

dPPF

• Proportional constant : 1 (cgs unit)

unit strength of pole

⇒1 cm, 1dyne force

(1dyne : 1g x 1cm/sec2 )

F : Force

P₁P₂: pole strength

d : distance

1.2 Magnetic pole

d

HpF

2dpH 1 Oe : 1 dyne for unit pole

Definition : field strength

O Field strength, H

HF

Christian Oersted(1775 ~ 1851)

1820년 4월 어느날 저녁 강연중에 그는 전류에 의해 자침이 움직이는 것을 발견하였다. 이 발견이 중요하다는 것은 급속히 인식되었다. 그는 유능한 스승이자 강연자였고 많은수의 저작을 남겼다. 그는 또 과학적인 지식을 일반 대중에게 알리는데 진략하였다

O 자기 모멘트 (magnetic moment)

(a) (b)

O 자화강도, 자화 (magnetization : M)

)(2)2()(2)2(blplpmalplpm

l l2

Vlp

VmM HmE

unit : ergs/Oe. cm3 = emu/cm3

emu/g

1.3 Magnetization

1.4 Magnetic induction B

Current : production of H

H : cause M

Magnetic induction B = H + 4 M (cgs)

o unit

H : Oersted (Oe)

M : emu/cm3

B : gauss (G)

(SI) )( MHB o

SI : originated from current

O unit conversion

H : 1 A/m = 4 x10-3 Oe

B : 1 T = 104 G

M : 1 weber/m2 = 104/4 emu/cm3

O H unit : (A/m)

O B unit : 1 weber/m2 (tesla : T)

flux

1 weber (Wb) = 1V . 1S

= 108 Mx

riH2

r

i

1 turn coil

(variation with same ratio)

B

1.5 SI unit

1.6. Kinds of magnetism

Macroscopic characteristics

Temperature dependence

permeability, susceptibility

O 투자율 (permeability) :

ΗΒμ

= 1 + 4

(B = H + 4 M)ΗM41

ΗΜx

O 자화율 (susceptibility) :

O Magnetic materials

반자성 (diamagnetic) : ~ - 2 10-6 (Cu, He)

상자성 (paramagnetic) : ~ + 2 10-5 (Na, Al)

강자성 (ferromagnetic) : ∼ 103 (Fe, Co, Ni)

페리자성 (ferrimagnetic) : (Fe3O4 )

Magnetic characteristics

Magnetic moment Field ??

Current : production of H

H : cause M

Magnetic induction

o unit

H : Oersted (Oe)

M : emu/cm3

B : gauss (G)

)mVsA 104(

(SI) )(1-1-7

o

o MHB

O unit conversion

H : 1 A/m = 4 x10-3 Oe

B : 1 T = 104 G

M : 1 weber/m2 = 104/4 emu/cm3

23 mA10emu1 ergs/Oe. cm3 = emu/cm3 emu/g

H

B4 M

H

(cgs) )4( MHB

1.7 Unit conversion

-4000 -2000 0 2000 4000-100

-80

-60

-40

-20

0

20

40

60

80

100

SMT-01Sapplied field: 5 kOe

Ms: 82.1 emu/gDate: Nov. 2nd. 2010

M (e

mu/

g)

Field(G)

How to change from emu/g to gauss ??

VSM curve !!

??

density :emu/cm emu/g 1 3

(gauss)G 4 (tesla) T 104emu/cm 1 4

3

(gauss)G 4 emu/g 1

(gauss)G 4500 emu/g 500 :example,For

rM

m web/A104 7 oμ