jiunn-yuan lin 林俊源 institute of physics 交大物理所 national chiao tung university
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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
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?
?
Power consumption
Speed & power consumption of SFQ device
Quantumlimit
Thermal limit
SC device
Speed(sec/gate)
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 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
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
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
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.
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)
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
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
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