Nueva Técnica de Medición para la Caracterización de Materiales

A New Measuring Technique
for the Characterization of
Magnetic Materials in Pulsed
Magnetic Fields
Authors: J. H. Espina Hernández
Supervisors: Prof. Dr. R. Grössinger
Prof. Dr. E. Estévez Rams
Antecedents
• Thin superconducting films were measured
using an open-flat pick-up coil in very
strong magnetic fields. [Lagutin et al, Rev. Sci. Instr. 66 (8)
1995; Weckhuysen et al, Rev. Sci. Instr. 70 (6) 1999]
• It had been demonstrated the use of a pulsed
field magnetometer for the quality control in
the production of permanent magnets.
[Grössinger et al, IEEE Trans. Magn. 38 (5) 2002]
Hypothesis
• The local area measurements
contribute to the experimental study
of several physical phenomena.
General Objetive
• To develop a new measuring technique
in pulsed magnetic fields.
Objects of Study
• A thin-film pick-up
coil (TFC) designed at
the TU-Vienna [G.
Handreich, .., J.H. Espina-Hernández,
Sensors and Actuators A, 91:57-60,
2001]
• Features
cm2
– Aeff = 4
– R ≈ 125 kΩ
1 mm
– L ≈ 25 µH [Mohan et al, IEEE
of Solid-State Circuits 34 (10), 1999]
– C ≈ 55 pF [measured with the
Kiethley 3322 LCZ meter]
• Wire wound pick-up
coil (WWC) produced
by MAGNET-PHYSIK
Dr. Steingroever
GmbH, Germany [ Dr.
Steingroever and Dr. Ross, Magnetic
Measuring Techniques, 1997]
• Features
– Aeff ≈ 5
– R ≈ 50 - 100 Ω
cm2
.
1 mm
– L ≈ 42 µH [measured with the
Kiethley 3322 LCZ meter]
Specific objetives
• To analyze the electrical behavior of the TFC and the
WWC.
• To demonstrate the possibility to calibrate the
magnetization for the local area measurements.
• To demonstrate the advantages and disadvantages of
the measurements using this type of pick-up coil sample arrangement in comparison to the standard
pick-up coils.
• To establish that the local eddy current measurements
contribute to the improvement of the correction of this
unlike effect, with the aim to incentive the application
of the pulsed field magnetometer as standard quality
control machine at the magnet production industry.
Pulsed Field Magnetometer (PFM)
Electrical circuit of a PFM
U max − β ⋅t
⋅ e ⋅ sen(ω ⋅ t )
if =
ω ⋅ LF
U max
dH
=
⋅ e − β ⋅t ⋅ [ω ⋅ cos(ω ⋅ t ) − β ⋅ sen(ω ⋅ t )]
dt ω ⋅ AeffF
Compensation of a pick-up coils
system
Vinds
dH
dM 

= µ 0 ⋅ Aeffp ⋅  LM ⋅
+ K1 ⋅

dt
dt 

Vindc
dH 

= µ 0 ⋅ Aeffp ⋅  LM ⋅

dt 

Vout = Vinds − Vindc
dM
→
dt
Zerosignal is always present, it
should be saved in the PC
Method to obtain the hysteresis loop
• A first shot with the sample, (Vind=VM+VZ)
• A second shot without sample, (VZ)
Hysteresis loop
tT
∫ (V
ind
t0
− Vz )
Plastic rod
DB-15
connector
BNC connectors
Field Coil
Volumetric Pickup LPC
Working station
Holders for the TFC and WWC
Plastic rod
Sketch of the local
area magnetization
measurements
Electrical study of the TFC and
the WWC
Zerosignal obtained by
simulation for the TFC
∆C = 0.1 nF
∆ϕ
Zerosignal obtained by
simulation for the WWC
∆C = 0.1 nF
ϕ cte
1.0
Hysteresis
loop for a
Ba-M sample
obtained
with the
WWC and
the TFC
M/Mo (a.u)
0.5
0.0
WWC
TFC
-0.5
-1.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
µ0Hext (T)
The high impedance of the TFC pick-up does not
affect the shape of the loop.
Calibration using the WWC
and the TFC
Calibration of H
Volumetric pick-up coils systems
• measuring well known
phase transitions; i.e: the
spin-flop of the MnF2
(µ0Hcr = 9.2 T a 4.2 K)
• measuring HA of Ba-M,
the singularity shows up
at 1320 kA/m, and it
changes 1 % from 300 330 K
For low Temp.
For high Temp.
Systems with the TFC and the WWC pick-up
Aeff is known !!!
vindp = Aeffp ⋅
K0
ω
⋅ e−β ⋅t ⋅ [ω ⋅ cos(ω ⋅ t ) − β ⋅ sen(ω ⋅ t )]
1.5
Data: DHDTCILIN8MF_DHDT
Model: PulseField
1.0
Vind (V)
0.5
Chi^2
R^2
= 0.00377
= 0.98961
k
w
B
Ae
2136.77623
752.5896
88.02241
0.00055
Accuracy around 1 %
±9.2678
±0.70624
±1.13975
±0
0.0
-0.5
-4
Induced Signal 2,5 T
Fit
-1.0
0.000
0.002
2
Aeffect=5.459 x 10 m
µ0Hmax=2.379 T
µ0H0=2.84 T
Holder SCD, 8 mF, 1.1 kV
0.004
t (s)
0.006
0.008
CalSCDHolderCilindro.OPJ
Room Temp
Calibration of M
Volumetric systems
• It is defined a
calibration sample (Ni,
Fe, Fe3O4, BaFe12O19)
with well known
parameters (m, MS).
CM =
M S _ C ⋅ VolC
∫ Vind _ V
C
[Am
2
/V ⋅ s
]
• Sample under
investigation
1
M y = ∫ Vind _ Vi ⋅ C M ⋅
Voli
• In case that
M y = M S _C
[A / m]
VolC = Voli
Vind _ V
∫
⋅
∫ Vind _ V
i
c
Local pick-up coils
10 cylinders, d=10 mm y
1 mm < h < 10 mm
Maximum of the Vint ~ M (V.s)
12
Complex behavior of the
induced signal respects
to the volume of the
sample
10
8
6
4
2
0
2
4
6
8
Height of the sample (mm)
10
Local Measurements,
Applications
Local demagnetizing factor measurements
∂nM
∂H n
SPD technique
HA measurement
Asti and Rinaldi, J. Appl. Phys.,
45 (8), Aug. 1974
BaFe12O19
n=2
H Aint = 1.65T , J S = 0.41T
N mL
H Aext − H A int
=
JS
Sample
Teo.
In. Mid. Out.
B1
0.7636 0.73 x
x
B2
0.668
x
B3
0.5807 0.6
BL1
0.9045 0.96 0.73 0.65
BL2
0.7323 0.74 0.73 0.34
0.68 x
x
The theoretical values of Nm are valid only at the
center of the sample
The study of the homogeneity of the stray field, the
demagnetizing field and the magnetization
x
Measurement of the transverse susceptibility
∆H
H st
∂n χt
∂H n
Asti and Rinaldi, J. Appl. Phys.,
45 (8), Aug. 1974
Singularity occurs at
HA
Paretti and Turilli, J. Appl. Phys.,
61 (11), Jun. 1987
vind t = k ⋅ χ t ⋅ h0 ⋅ ω ⋅ sen(ω ⋅ t )
Amplificador Look-in
Eddy current measurements
Previous work by M. Kuepferling et al
dH
m = k (σ ,..) ⋅
dt
kCu ρ Al
=
k Al ρ Cu
mCu ρ Al
=
m Al ρ Cu
The relationship is linear if the following conditions are
fulfilled:
•Hext is homogeneous and isotropic
•The conductivity of the sample is not too high and
the parasitic field ~ external field
•R sample and R magnet < wavelength of the field
A phase shift between M and H exists and is 90 deg
Eddy currents
depend on the radius
of the sample
h = 8 mm, 10 mm ≥ d ≥ 2 mm
Eddy currents keep
constant with the
height of the sample
d = 4 mm, 10 mm ≥ h ≥ 2 mm
m is proportional to dH/dt
linear
Local eddy current measurements
Al and Cu discs
h = 5 mm d = 5; 11; 18; 26; 35 mm
At the inner position (Mi)
the eddy current loops
agreed with the results of
Kuepferling et al for d <
12 mm
Conclusions
1- It was demonstrated that a high impedance pick-up
coil is quite sensitive to small capacitance variations and
noise, what limit ist application in a pulsed field
magnetometer. Nevertheless, the high impedance does
not affect the shape of the loop if the pick-up coils
system is well compensated.
2- It was demonstrated the calibration of the local area
magnetization measurements in physical units, when the
samples have the same volume.
3- The local area measurements are very sensitive to the
sample’s geometry, what allows using them as a tool for
the quality control in the industrial production of
permanent magnets.
4- It was obtained the local demagnetizing factor for
samples with different dimensions, and it was
demonstrated the possibility of performing study of the
homogienity of the magnetization along the radius of the
sample. It was also demonstrated experimentally, that the
theoretical value of Nm is an approximation only valid at
the center of the sample.
5- It was demonstrated the possibility of performing
transverse susceptibility measurements in a PFM. We
are unaware of any previous attempt.
6- It has been demonstrated that a PFM is, in many
instances, an indispensable instrument for the
characterization of magnetic materials in the laboratory
as well as in the industry.