Radiant Technologies, Inc.
Measuring Magnetoelectric
and Magnetopiezoelectric
Effects
Scott Chapman, Joe T. Evans, Jr., Bob Howard,
Spencer Smith, Allen Gallegos
Radiant Technologies, Inc.
AMF
December 11, 2012
Radiant Technologies, Inc.
Summary
• Magnetoelectric effect
• Standard Voltage Measurement
• Charge-Based Measurement
– Procedure
– Results
• Conclusion
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Magnetoelectric Effect
Voltage Measurement
E = ME x H
• Dr. Shashank Priya of the Center for Energy Harvesting Systems and
Materials (CEHMS) asked Radiant to develop a calibrated test for
magnetoelectric properties.
• Radiant testers measure charge so we suggested the following test:
Charge Measurement
P = x H
V
H
Q
H
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Voltage Measurement
Gauss
Meter
Lock-In Amplifier
OUTPUT INPUT
Helmholtz Coil
H Field Axis
Field Coil
DC
Power
Supply
1. Establish strong DC Bias H-Field with Electromagnet
2. Apply Small-Signal Sinusoidal Current to HH Coil.
3. Measure Sinusoidal Voltage on Sample.
4. Plot Voltage Amplitudes Vs DC Bias.
1 Gauss - 1 kHz
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0 200 400 600 800 1000
0
2
4
6
8
10
12
DC Bais Field (Oe)
ME
Co
eff
icie
nt
(mV
/cm
Oe
)
ME Response
Each point is individually measured by hand.
Sample synthesized and characterized by S. C. Yang, Center for Energy Harvesting
Materials and Systems (CEHMS), Virginia Tech. Copyright belongs to CEHMS.
Radiant Technologies, Inc.
Charge Measurement • The ferroelectric tester captures charge generated by the sample as the
H field varies.
HVA
I2C Port
SENSOR 2
Premier II
DRIVE RETURN USB to
host
HH Coil Current Amplifier I 2C
DAC
Field Coil
H- Field
Sensor
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Comparison of Techniques • Dr. Chee-Sung Park (Va. Tech - CEHMS) showed that the two test
techniques, measuring charge or measuring voltage, produced the
same result if the variation of the sample dielectric constant with
applied magnetic field is included in the calculations.
[Smart Mater. Struct. 20 (2011) 082001 (6pp)]
• Radiant set out to automate and calibrate the charge-based procedure.
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Experimental Setup • No field coil was used in the present experiment.
• No H-Field Sensor was used. Current into the H.H. coil was captured.
Reliability of current detection was calibrated with an H-Field sensor
offline.
Precision Multiferroic
DRIVE RETURN USB to
host
Helmholtz Coil
Current Source
Current Sensor
SENSOR 1
H-field
• The Helmholtz coil
was capable of ±50
Oersted.
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Test Procedure
• The charge-based magneto-electric measurement is an exact analog to
the traditional polarization hysteresis measurement.
• The tester drives H and measures P.
• = P/ H.
Electrically Generated Polarization:
Tester
Magnetically Generated Polarization:
Tester
H
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Measuring H by Hall Effect vs
Current Sensor • The Hall Effect sensor is accurate and directly measures the magnetic
field but is sensitive to misalignment in three dimensions.
• The current sensor can capture the current within 1% and is used with
the coil geometry to calculate the magnetic field in the Helmholtz
volume.
• The current sensor has proven to be reproducible and eliminates the
need for complex modifications to the shield box.
PMF
Tester
DRIVE
SENSOR1
SENSOR2
RETURN
Hall Effect Sensor
Current Amp Current Sensor
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Knowing the Value of H is a
Challenge • The magnetic field at, within or through the sample under test is
dependent on:
o H.H. Coil field by input current
o Sample position
o Sample orientation
o Sample geometry
• The Vision program includes a geometry term to correct for the
geometry variances.
• The data presented here were taken with the sample at the H.H. coil
centerline. This is a region of constant H at the calibrated H.H. coil
value.
• For the data presented here, geometric errors still exist, but were
considered minimal so the geometry term was fixed at 1.0.
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Nullified Parasitics
The virtual ground input of the
polarization tester maintains zero
volts on one side of the sample.
The sample is grounded
on the other side.
The external test circuit adds no
parasitics to the test. Only the
input parasitics of the tester must
be characterized and subtracted.
Since the tester steps and waits at each
point, the magnetic field is not changing
when each charge value is captured.
TP1
Twisted Pair Self-Capacitance
Coax Capacitance
Virtual Ground Input
Sample
+ ME
voltage source
-
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Benefit of a Shield Box
-40
-30
-20
-10
0
10
20
30
40
-60 -40 -20 0 20 40 60
Pic
oco
ulo
mb
s
Oersted
Corrected Charge
- 2 . 0
- 1 . 5
- 1 . 0
- 0 . 5
0 . 0
0 . 5
1 . 0
1 . 5
2 . 0
- 4 0 - 3 0 - 2 0 - 1 0 0 1 0 2 0 3 0 4 0
S i n g l e M E R e s p o n s e
Ch
ar
ge
(
pC
)
M a g n e t i c F i e l d ( O e )
S a m p l e M E R : 1
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Typical Test Setup
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Shield Box
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Composite Sample • Five loops executed over a ±45.0 Oe sweep at 1 Hz.
• Sample: 1mm Thick KNaNbO-LiSbO-NiZnFeO
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
-40 -30 -20 -10 0 10 20 30 40
Ch
ar
ge
(p
C)
M ag n et ic F ield (Oe)
Sam p le M ER : 1 Sam p le M ER : 2 Sam p le M ER : 3
Sam p le M ER : 4 Sam p le M ER : 5
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Tester Parasitics with Fit • The parasitics were measured using the same test procedure with the
exception that the shield box was disconnected from the virtual ground
input of the tester.
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
-40 -30 -20 -10 0 10 20 30 40
T e s te r P a ra s it ic s
Ch
ar
ge
(p
C)
M ag n et ic F ield (Oe)
A v erag e Paras i t ic s : ST L A . F i l t er : 1 A v erag e Paras i t ic s : STL A . F i l t er : 1 F i t
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4th Order Polynomial Curve Fit
-2 .0
-1 .5
-1 .0
-0 .5
0 .0
0 .5
1 .0
1 .5
2 .0
-4 0 -3 0 -2 0 -1 0 0 1 0 2 0 3 0 4 0
4 th O rd e r F it to D iffe re n c e C u rv e
Ch
arg
e (
pC
)
M a g n e tic Fie ld (Oe )
Sa m p le Avg - Pa ra s itics Avg : Tw o -Tra ce M a th Filt
Sa m p le Avg - Pa ra s itics Avg : Tw o -Tra ce M a th Filt
Q(pC) = -6.84x10-3 h + 1.80 x10-3 h2 - 8.50 x10-7 h3 - 1.08 x10-7 h4
R-Square: 0.9987
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Small Signal Capacitance (nF) Vs Field (Oe)
• Interpolated Capacitance at 40.0 Oe = 0.346 nF
0.3459
0.3460
0.3461
0.3462
0.3463
0.3464
-40 -30 -20 -10 0 10 20 30 40
4 th O rd e r F it o f C V v s M a g F ie ld
Ca
pa
cit
an
ce
(n
F)
M ag n et ic F ield (Oe)
P lo t CV vs -Mag fi eld : S in g le-P o in t Fi l ter : 1 P lo t CV vs -Mag fi eld : S in g le-P o in t Fi l ter : 1 F i
P lo t CV vs +Mag fi eld : S in g le-P o in t Fi l ter : 1 P lo t CV vs +Mag fi eld : S in g le-P o in t Fi l ter : 1 Fi
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
-40 -30 -20 -10 0 10 20 30 40
4th Order Fit of CV vs Mag Field
Ca
pa
cit
an
ce
(n
F)
Magnetic Field (Oe)
Plot CV vs -Mag field: Single-Point Filter: 1 Plot CV vs -Mag field: Single-Point Filter: 1 Fi
Plot CV vs +Mag f ield: Single-Point Filter: 1 Plot CV vs +Mag f ield: Single-Point Filter: 1 Fi
R-Square:
Positive = 0.9373
Negative = 0.9760
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vs ME
• The charge generated by the 0.981cm2 , 0.1cm-thick sample is fit by
the following equation:
Q(pC) = -6.84x10-3 h + 1.80 x10-3 h2 - 8.50 x10-7 h3 - 1.08 x10-7 h4
• Divide Q by the sample area to arrive at the polarization prediction
and then take the derivative to find the slope of P as a function of H
within the test window.
= -7.45x10-3 + 3.92 x10-3 h – 2.78 x10-6 h2 - 4.71 x10-7 h3
(pC/cm2/Oe)
• At 40 gauss, for this sample is 0.115 pC/cm2 / Oe.
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vs ME
• To calculate the ME for the sample, start again with the charge
equation.
Q(pC) = -6.84x10-3 h + 1.80 x10-3 h2 - 8.50 x10-7 h3 - 1.08 x10-7 h4
• Divide Q by the sample capacitance to arrive at the voltage the
capacitor would produce open circuit with that charge. Since the
small signal capacitance varies with magnetic field strength, this
solution is valid only at a specific magnetic field.
• Divide by the thickness to get the electric field and take the derivative
to achieve the equation for the ME coefficient.
ME = -1.94x10-4 + 1.02 x10-4 h – 7.22 x10-8 h2 – 1.22 x10-8 h3
(mV/cm/Oe)
• At 40 gauss, ME for this sample is 2.99 mV/cm / Oe.
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Conclusion • The charge-mode determination of accurately generates a
charge vs magnetic field plot of the sample in an AC magnetic
field.
• The charge-mode measurement is free of parasitic charge
contributions.
• Placing the sample inside a metallic shield box inside the
Helmholtz coil enables low noise measurements of picocoulomb
charge values.
• Our next step is to embed the current sensor into the current
source coupled with a self-aligned shielded sample holder with
precision sample rotation.
Radiant Technologies, Inc.
Acknowledgement
• The authors would like to acknowledge the assistance and
cooperation of:
• Dr. Shashank Priya
• Dr. Chee-Sung Park
• Mr. Shashaank Gupta
• Mr. Su Chul Yang
all at the Center for Energy Harvesting Materials and
Systems of Virginia Tech.
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56 Oe Fixed Bias
• The magnet is at 2.0 cm from sample along the coil field
axis. The DC Magnetic field was measured at 56 Oe using a
Lakeshore 425 Gauss meter.
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VT Composite Sample - ±45.0 Oe Sweep
Fixed Bias (±56 Oe) and Unbiased
• The magneto-electric coefficient is the slope of the sample response at
each field point of the composite loop, above.
Point Under
Consideration