자성 특성 측정 방법
자기장 측정
M-H 자기이력 곡선 : SQUID, VSM
고주파 특성 (투자율)
자기 센서 기술 연구 동향
By Honeywell NVE
InSb
지구 자기장
(1) 자기장 측정
휴대폰용 COMPASS 센서 응용
Magneto-Impedance Hall
Micro-Size
SQUID Flux gate
0.1 nT
AMR
30 nT 1 nT
0.1 nT
Low power Low Cost ?
1 fT
차세대 compass - 성능
- 가격
센서
소자 ASIC Package
& Test
+ +
=
지구 자기장
COMPASS 센서의 가격 절감 요소
센서 소자
Size 감소
재료비 절감 단가 절감
성능 향상
휴대폰 연동
민감도 향상
각도 분해능 향상 Offset 최적화
ASIC
회로비용 절감
AMP Gain A/DC
By Aichi Steel
가속도 센서 병행 사용
단가 절감
Red ocean
COMPASS 센서의 가격 절감 요소
휴대폰과 연동
자기장 발생원 : 스피커, 진동자 등
최적의 위치 선점 : ASIC Offset 기능 최적 화
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) 센서 Size : 5mm X 5mm X 1.2mm
E-compass 응용
• Hall 효과 방법
) /
, /
1 (
) width :
(
,
) (
wt I
J ne t R
IB V R
w w
E V
v ne ne J
B B J
v E
H H
H
H H
H
홀전압
전기장 홀
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 susceptometer H = 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 = 103A/m m
(magnetic moment) emu A.m2 1 emu =10-3A.m2
M-H vs B-H Loop (2) 자기 물성 측정
Magnetometer
Sensitivity (emu) Dynamic
range Applications
χac 10-9 Wide
phase transitions superparamag.
superconductors
not quite abs. magnetization
demanding instrumentation low T/high pressure
Maintenance cost : low
Torque 10-3~ 10-8(cap.) 10-9~ 10-11(piezo)
narrow very narrow
phase transitions
magnetization anisotropy Superconductors
small signal for polycrystal difficult to calibrate Maintenance cost : middle
SQUID 10-8~10-11 narrow
all above
absolute magnetization
Very high sensitivity Hybrid magnet
Speed : slow
Maintenance cost : high
VSM
10-6
(0.5 uemu ~ 1000 emu)
Wide
all above
absolute magnetization
low sensitivity
Temperature : 10 ~ 1073 K Maintenance cost : low Size : > 15mm (Pole cap) Mass : 10g
AGM
10-8
(1 nemu ~ 10 emu) middle
all above
absolute magnetization
middle sensitivity
Temperature : 10 ~ 473 K Maintenance cost : low Size : 5x5x2 mm
Mass : 0.2g
자화율 측정
) (
) (
) :
(
V M m
B m
U U
F
위치에너지
힘
) sample,
of outside field
: (
) (
2
1
2
H μ B
B
H M
z V H z V
M B F
o o
• 진동 시료법 (Vibrating Sample Magnetometer : VSM)
전자기 유도 방법
NA dt B
dt t NAB d
d
1
) (
: :
: :
N A
자속 ( maxwells ) 유도 전압 ( Volt ) 면적 ( cm2) 권선수
Introduction
• Magnetic measurement is a powerful method to characterize properties of materials.
• Among numbers of magnetic measurement equipment, Vibrating sample magneto-meter (VSM) is known as a very effective way to determine magnetization.
• VSM offers different measuring modes. By analyzing the results, many useful 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 Principle
Magnetization 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 M The accuracy is not high.
BA
V NA dB dt B
0( H M ) NA 1 Vdt
I N
S S
I N
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.
t sin
t M
t M
NA t
dt M NA d
dt NA dM
dt NA dH
M dt H
NA d dt
NA dB V
cos cos
sin 0
) (
0 0
0 0
0
0 0
0
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-in amplifier Oscillator (~ 80 Hz)
Computer Magnetization
Reference
H-field
4 coils
Sample
Vibration
t t
v
) (
) (H
kAfm
moment magnetic
:
frequency vibrating
: area :
constant coil
:
m(H) f A k
) ( t
VSM Sensitivity & Noise
The 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, Bror Mr) 5) 보자력 ( Coercivity, Hc)
6) 포화자화
(Saturation, magnetization Bsor Ms)
Field (Oe)
-15000 -10000 -5000 0 5000 10000 15000
Magnetic moment (EMU)
-0.015 -0.010 -0.005 0.000 0.005 0.010 0.015
Parallel to the field
Perpendicular to the fielddiamagnetic Ferromagnetic
or 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 range
VSM 10-6 Wide [1,5]
AGM 10-8 Middle [2,5]
SQUID 10-8~ 10-11 Narrow [3,5]
1. www.lakeshore.com
2. W.Ross et.al., Rev.Aci.Instrum., 51,612 (1980)
3. J. Diederichset.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)
2 3
20 10 A m
10 emu
1 B
Measurable field : ~ fT (~10−15 T) SQUID
Dipole field
r e
e m r
H m r sin ˆ
4 ˆ 1 4 cos
2
3
3
T 10 10
T 10
: resolution moment
Same
10 /
) m (10
m 10
: system Our
) m (10 cm
: SQUID
6 - 9
15 -
3 9
5 - -2
PHR SQUID
PHR SQUID
r r
r r
