measuring magnetoelectric and magnetopiezoelectric effects€¦ · •dr. shashank priya of the...

Radiant Technologies, Inc.

Measuring Magnetoelectric

and Magnetopiezoelectric

Effects

Scott Chapman, Joe T. Evans, Jr., Bob Howard,

Spencer Smith, Allen Gallegos


AMF

December 11, 2012


Summary

• Magnetoelectric effect

• Standard Voltage Measurement

• Charge-Based Measurement

– Procedure

– Results

• Conclusion


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


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


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.


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


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.


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.


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


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


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.


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

-


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


Typical Test Setup


Shield Box


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


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)


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


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


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)


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


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.


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.


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.


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.


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.


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

measuring magnetoelectric and magnetopiezoelectric effects€¦ · •dr. shashank priya of the...

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