자성 특성 측정 방법

자기장 측정

M-H 자기이력 곡선: SQUID, VSM

고주파 특성 (투자율)

자기 센서 기술 연구 동향

By Honeywell

NVEInSb

지구 자기장

(1) 자기장 측정

휴대폰용 COMPASS 센서 응용

Mag

neto

-Impe

danc

e

Hal

l

Micro-Size

SQ

UID

Flux

gat

e

0.1 nTA

MR

30 nT

1 nT

0.1 nT

Low power

Low Cost ?1 fT

차세대 compass- 성능- 가격

센서

소자ASIC Package

& Test++=

지구 자기장

COMPASS 센서의 가격 절감 요소

센서 소자

Size 감소

재료비 절감

단가 절감

성능향상

휴대폰연동

민감도 향상

각도 분해능 향상

Offset 최적화

ASIC

회로비용 절감

AMP GainA/DC

By Aichi Steel

가속도 센서병행 사용

단가 절감

Red ocean

COMPASS 센서의 가격 절감 요소

휴대폰과 연동

자기장 발생원 : 스피커, 진동자 등

최적의 위치 선점 : ASIC Offset 기능 최적화

By Aichi Steel

최적의 위치

-15 -10 -5 0 5 10 15

-0.10

-0.05

0.00

0.05

0.10

V out

Magnetic Field (Oe)

동작점 이동

수평

3차원 지자기(방위) 센서Size : 5mm X 5mm X 1.2mm

E-compass 응용

• Hall 효과 방법

)/ ,/1(

)width:( ,

)(

wtIJneRtIBRV

wwEV

vneJneBJBvE

HH

H

HH

H

홀전압

전기장홀

측정범위 : 수 Oe ~ 수십 KOe

Hall 효과

V = RH B

I

B

V

SI : B = μH = μ0 (H+M) = μ0 (1+χ)H (χ=M/H : susceptibility)

cgs : B = H + 4πM B = Magnetic flux density, Magnetic induction susceptometerH = Magnetic field strength experimentally controllable (Current)

M = (Volume) Magnetization magnetometer

WHAT WE MEASURE: B OR M

cgs SI Conversion

B G T, Wb/m2 1 G = 10-4 T

H Oe A/m 1 Oe = 103/4π A/m

M emu/cm3 A/m 1 emu/cm3 = 103 A/m

m(magnetic moment)

emu A.m2 1 emu =10-3 A.m2

M-H vs B-H Loop

(2) 자기 물성 측정

MagnetometerSensitivity (emu) Dynamic

range Applications

χac 10-9 Wide

phase transitions superparamag. superconductors not quite abs. magnetization

demanding instrumentationlow T/high pressureMaintenance cost : low

Torque10-3 ~ 10-8 (cap.)10-9 ~ 10-11(piezo)

narrowvery narrow

phase transitionsmagnetization anisotropySuperconductors

small signal for polycrystaldifficult to calibrateMaintenance cost : middle

SQUID 10-8~10-11 narrow

all aboveabsolute magnetization

Very high sensitivityHybrid magnetSpeed : slowMaintenance cost : high

VSM 10-6

(0.5 uemu ~ 1000 emu)

Wide

all aboveabsolute magnetization

low sensitivityTemperature : 10 ~ 1073 KMaintenance cost : lowSize : > 15mm (Pole cap)Mass : 10g

AGM10-8

(1 nemu ~ 10 emu)middle

all aboveabsolute magnetization

middle sensitivityTemperature : 10 ~ 473 KMaintenance cost : lowSize : 5x5x2 mmMass : 0.2g

자화율 측정

) ( )(

):(

VMmBm

UUF

위치에너지힘

) sample, of outside field:(

)( 21

2

HμBB

HMVzH

VzBMF

o

o

• 진동 시료법 (Vibrating Sample Magnetometer : VSM)

전자기 유도 방법

dtNA

B

dt

NABtdd

1

)(

::::

NA 자속 ( maxwells )

유도 전압 ( Volt )면적 ( cm2 )권선수

Introduction

• Magnetic measurement is a powerful method to characterize properties ofmaterials.

• Among numbers of magnetic measurement equipment, Vibrating samplemagneto-meter (VSM) is known as a very effective way to determinemagnetization.

• VSM offers different measuring modes. By analyzing the results, manyuseful information of materials can be extracted.

- Magnetic field (electro magnet, Power supply)

- Detection part (pick-up coil→Lock-in(m), Gaussmeter(H))

- Vibrating part (loud speaker, feedback system, power supply)

- Display & controller (Computer, Software)

Vibrating Sample Magnetometer (VSM)

Electromagnet Power supply Electromagnet

Vibrator

Vibrator power

Lock-in & Gaussmeter

Computer

Pick-up coil

If a sample of any material is placed in a uniform magnetic field, created between the poles of a electromagnet, a dipole moment will be induced.

If the sample vibrates with sinusoidal motion a sinusoidal electrical signal can be induced in suitable placed pick-up coils.

The signal has the same frequency of vibration and its amplitude will be proportional to the magnetic moment, amplitude, and relative position with respect to the pick-up coils system.

VSM Operation Principle

VSM Operation PrincipleMagnetization is often measured by induction method (for example in an extraction magnetometer):

V: Induction voltage N: Number of coils: magnetic flux t: time A: area of coil

This method only measures B, not MThe accuracy is not high.

BA dtdBNAV Vdt

NAMHB 1)(0

I N

S S

NI

VSM: sample is vibrating with a standardized frequency ( ) during the measurement.H does not depend on t but M depends on t :

AC measurements always improve signal to noise ratio.By this method, the signal is directly proportional to magnetization.

tsin

tMtMNAtMdtdNA

dtdMNA

dtdHNAMH

dtdNA

dtdBNAV

coscossin0

)(

00000

000

VSM Operation Principle

VSM Sensitivity

The voltage V(t) across the VSM detection coils can be written as

Magnetic moment: selection of the sample volume can be used to optimize signal; in general, larger is better; size may affect B uniformity & vibration load.

Vibration amplitude: large amplitude increases sensitivity (if coils are large enough to capture full excursion with uniform sensitivity).

Vibration frequency: higher freq. gives higher sensitivity, but other constraints limit max usable freq. (eddy currents in conducting samples, audio noise due to vibrator, interference from harmonics/subharmonics of power freq.).

Detection coil sensitivity: coupling of detector is strong function of (inverse) separation between sample & coils; small separation makes sample mounting & shape issues more important.

Lock-inamplifier

Oscillator(~ 80 Hz)

Computer

Magnetization

Reference

H-field

4 coils

Sample

Vibration

ttv

)(

)(HkAfm

momentmagnetic:frequency vibrating:

area:constantcoil:

m(H)fAk

)(t

VSM Sensitivity & NoiseThe main sources of noise to limit VSM sensitivity comes from background signals and the signal-to-noise ratio (SNR).

A. Background signals

These can include vibration of the detector coils due to mechanical coupling from the sample vibrator (need to insure vibration isolation here). Also stray signals can come from wire loops or drive wires leading to the vibrator (independent of B and present without a sample). Also pickup from other power sources (electrical & mechanical vibrations).

B. Noise in VSM

The main sources of noise include the usual culprits (Johnson, Shot, and 1/f noise). Johnson noise (thermal noise due to e– fluctuations in R) is usually the most significant in VSM. It is given by

VRMS = (4kTRf)1 / 2

where k = Boltzmann’s constant T = absolute T

R = coil resistance f = freq. bandwidth of measure in Hz

M-H, B-H Loop (Hysteresis Loop)1) 자기소거 (demagnetized state)

2) 초기곡선 (initial curve)

3) 이력곡선 (hysteresis loop)

major loop

minor loop

4) 잔류자화

( Remanence magnetization, Br or Mr)

5) 보자력 ( Coercivity, Hc )

6) 포화자화

(Saturation, magnetization Bs or Ms)

Field (Oe)-15000 -10000 -5000 0 5000 10000 15000

Mag

netic

mom

ent (

EMU

)

-0.015

-0.010

-0.005

0.000

0.005

0.010

0.015Parallel to the field

Perpendicular to the fielddiamagnetic

Ferromagneticor Paramagnetic

• 연자성 : 작은 보자력 , 자화 • 탈자가 쉬움 • 경자성 : 큰 보자력 , 자화 • 탈자가 어려움

- Transformers- Magnetic Shield- Flux keeper for relays, printer,- motors, watches, and other magnetic system

- Motors- Linear motors- Headphone- Balances- Microwave tubes, laser

“hard” ferromagnetic material has a large Mr and large Hc.

“soft” ferromagnetic material has both a small Mr and Hc.

-50 L : 0.165 emu at10,000 Oe(3 emu/cc)

7 10-3 emu at 15 Oe

- Drop of 40 pL : ~ 6 10-9 emu

-Signal intensity : 15 V - Noise level : 0.5 V

Resolution : 2 10-10 emu

(3) CNU Droplet 방법 !!

Magnetometer Sensitivity (emu) Dynamic rangeVSM 10-6 Wide [1,5]AGM 10-8 Middle [2,5]

SQUID 10-8 ~ 10-11 Narrow [3,5]

1. www.lakeshore.com2. W.Ross et.al., Rev.Aci.Instrum., 51,612 (1980)3. J. Diederichs et.al., Czechoslovak J. Phys., 46, 2803 (1996)4. A. Bogach et.al., J. Electrical Engineering, 59, 11(2008)5. C.D.Graham et.al., J.Mater.Sci.Technol., 16,97(2000)

2320 mA 1010emu 1 B

Measurable field : ~ fT (~10−15 T)

SQUID

Dipole field

erme

rmH r ˆ sin

41ˆ cos

42

33

T1010T10 :resolutionmoment Same

10/

)m (10 m 10 :systemOur

)m(10 cm :SQUID

6-915-

93

5-

-2

PHRSQUID

PHR

SQUID

rr

r

r

HVm

Is it reasonable ?