Fundamentals of Magnetism

and Magnetic Measurements

Jiunn-Yuan Lin 林俊源Institute of Physics 交大物理所National Chiao Tung University

ContentsIntroduction to magnetismIntroduction to superconductivityThe best way of measuring the magnetic

moment-SQUID!Specification of MPMS

Fundamentals of magnetism

DiamagnetismParamagnetismFerromagnetismAntiferromagnetism

Diamagnetism

Due to Faraday’s law

AdB

dt

dE

B

B

Paramagnetism

T

CB

M

T

C

Ferromagnetism

Antiferromagnetism

Hysteresis

Magnetic domains

32

02

1dxBU

To minimized the magnetostatic energy

Magnetic Force Microscope (MFM)

Introduction to superconductivity

80 90 100 1100

50

100

150

T

c(K)

Year of discovery

70

Nb3Ge

MgB2

Metallic alloys

LSCO

YBCO

TI - cuprateHg - cuprate

Cuprates

e-doped LaOFePe-doped LaOFeAs

e-doped SmOFeAs

Fe-based superconductors

The Race to Beat Cuprates?

The crusade of Room Temperature superconductors?

？

Josephson effect (1962)

The electronic applications of superconductors

Power consumption

Speed & power consumption of SFQ device

Quantumlimit

Thermal limit

SC device

Speed(sec/gate)

SQUID

The SQUIDWithin a year of Brian Josephson’s discovery,

the first Superconducting Quantum Interference Device (SQUID) was built

In 1968, Professor John Wheatley of UCSD and four other international physicists founded S. H. E. Corp. (Superconducting Helium Electronics) to commercialize this new technology.

SQUID Magnetometers

The first SQUID magnetometer was developed by Mike Simmonds, Ph.D. and Ron Sager, Ph.D. while at S.H.E. Corporation in 1976.

In 1982, Mike and Ron, along with two other SHE employees, founded Quantum Design.

In 1984, QD began to market the next generation SQUID magnetometer – the Magnetic Property Measurement System (MPMS).

In 1996, QD introduced the MPMS XL as the latest generation SQUID magnetometer

During the past 22 years, six companies have unsuccessfully designed and marketed SQUID magnetometers to compete with the MPMS.

MPMS XL EverCool™ System

MPMS XL Temperature ControlPatented dual impedance design allows continuous

operation below 4.2 KSample tube thermometry improves temperature

accuracy and controlTransition through 4.2 K requires no He reservoir

refilling and recycling (no pot fills)Temperature sweep mode allows measurements

while sweeping temperature at user controlled rate Increases measurement speed

Smooth temperature transitions through 4.2 K both cooling and warming

MPMS XL Temperature Control

MPMS XL Temperature Control

MPMS XL Temperature Control

Temperature Range: 1.9 - 400 K (800 K with optional oven)Operation Below 4.2 K: ContinuousTemperature Stability: ±0.5% Sweep Rate Range: 0.01 - 10 K/min with smooth

transitions

through 4.2 KTemperature Calibration ±0.5% typical

Accuracy: Number of Thermometers: 2 (one at bottom of sample tube; one at

the location of sample measurements)

Magnetic Field Control

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11 tteessllaa 00..55 OOee 11..00 tteessllaa 00..0055 OOee 11550000 OOee 55 tteessllaa 11 OOee 55..00 tteessllaa 00..11 OOee 55000000 OOee 77 tteessllaa 22 OOee 77..00 tteessllaa 00..22 OOee 66000000 OOee

Very high homogeneity magnets (1, 5 and 7 Tesla) 0.01% uniformity over 4 cm

Magnets can be operated in persistent or driven mode Hysteresis mode allows faster hysteresis loop

measurementsMagnets have two operating resolutions: standard and high

resolution

Hysteresis Measurement

Reciprocating Sample Measurement System(RSO)

Improved measurement sensitivityIncreased measurement speed

No waiting for the SQUID to stabilize Very fast hysteresis loops up to 8x faster than conventional

MPMSServo motor powered sample transport allows

precision oscillating sample motionHigh precision data acquisition electronics includes a

digital signal processor (DSP) SQUID signal phase locked to sample motion Improved signal-to-noise ration

Low thermal expansion sample rods with sample centering feature

Reciprocating Sample Measurement System(RSO)

RSO Data The DC scan

took 56 hours to take 960 points

The RSO scan took 1600 points in under 24 hours!

The RSO scan avoids subjecting the sample to field inhomogeneities that effected the DC scan.

Hysteresis Mode DataThis measurement takes ~ 3.5 hours in persistent mode

Reciprocating Sample Measurement System

(RSO)

Frequency Range: 0.5 - 4 HzOscillation Amplitude: 0.5 - 50 mmRelative Sensitivity: < 1 x 10-8 emu; H 2,500 Oe, T = 100 K(for 7-tesla magnet)

6 x 10-7 emu; H @ 7 tesla, T = 100 K (for 7-tesla magnet)Dynamic range 10-8 to 5 emu (300 emu with Extended Dynamic Range option)

0 5 10 15 20 25 30-0.0020

-0.0015

-0.0010

-0.0005

0.0000

0.0005

M (em

u)

T (K)

Ba(Fe1-x

Cox)2As

2 (x=0.08) H

//ab=50 Oe

FC ZFC

MPMS System Options Transverse Moment Detection

for examining anisotropic effects Second SQUID detection system

SQUID AC Susceptibility 2 x 10-8 emu sensitivity 0.1 Hz to

1 kHz

Ultra-Low Field Reduce remanent magnet field to

±0.05 Oe

Extended Dynamic Range Measure moments to ±300 emu

External Device Control Control user instruments with the

MPMS

10 kBar Pressure Cell

Sample Rotators Vertical and Horizontal

Sample Space Oven Temperatures to 800 K

Environmental Magnetic Shields Fiber Optic Sample Holder

Allows sample excitation with light

Manual Insertion Utility Probe Perform elector-transport

measurements in MPMS

Liquid Nitrogen Shielded Dewar EverCool Cryocooled Dewar

No-Loss liquid helium dewar No helium transfers

SQUID AC SusceptibilityDynamic measurement of sample

Looks also at the resistance and conductance Can be more sensitive the DC measurement

Measures Real () and Imaginary () components is the resistance of the sample is the conductive part

Proportional to the energy dissipation in the sample

Must resolve components of sample moment that is out of phase with the applied AC field SQUID is the best for this because it offers a signal response that is

virtually flat from 0.01 Hz to 1 kHz

Available on all MPMS XL systemsRequires system to be returned to factory for upgrade

SQUID AC SusceptibilityFeatures

Programmable Waveform Synthesizer and high-speed Analog-to-Digital converter

AC susceptibility measured automatically and can be done in combination with the DC measurement

Determination of both real and imaginary components of the sample’s susceptibility

Frequency independent sensitivitySpecifications

Sensitivity (0.1 Hz to 1 kHz):2 x 10-8 emu @ 0 Tesla 1 x 10-7 emu @ 7 Tesla

AC Frequency Range: 0.01 Hz to 1 kHz AC Field Range: 0.0001 to 3 Oe (system

dependent) DC Applied Field: ±0.1 to 70 kOe (system dependent)

SQUID AC Susceptibility

Ultra-Low Field Capability

Actively cancels remanent field in all MPMS superconducting magnets

Sample space fields as low as ±0.1 Oe achievableCustom-designed fluxgate magnetometer suppliedIncludes Magnet ResetRequires the Environmental Magnet Shield

Hysteresis measurement

Extended Dynamic Range

Extends the maximum measurable moment from ± 5 emu to ± 300 emu (10 orders of magnitude)

Automatically selected when needed in measurement

Effective on both longitudinal and transverse SQUID systems

Sample Space OvenProvides high temperature measurement

capability Ambient to 800 K

Easily installed and removed by the user when needed

A minimal increase in helium usage Approximately 0.1 liters liquid helium/hour

3.5 mm diameter sample space

MPMS Horizontal Rotator

Automatically rotates sample about a horizontal axis during magnetic measurement

360 degrees of rotation; 0.1 degree stepsSample platform is 1.6 X 5.8 Diamagnetic background signal of 10-3 emu at 5 tesla

Manual Insertion Utility Probe

Perform electro-transport measurement in the MPMS sample space

10-pin connectorUse with External Device Control (EDC) for controlling

external devices (e.g., voltmeter and current source) Creates fully automated electro-transport measurement system

External Device Control

Allows control and data read back from third party electronics

Allows custom control of MPMS electronicsUse with Manual Insertion Utility Probe for

automated electro-transport measurementsMPMS MultiVu version written in Borland’s Delphi

(Visual Pascal) programming language

Fiber Optic Sample HolderAllows sample to be illuminated by an external light

source while making magnetic measurementsOptimized for near UV spectrum (180 to 700 nm) Includes 2-meter fiber optic bundleSample bucket 1.6 mm diameter and 1.6 mm deep

Slide seal

Fiber optic bundle

SMA connector