Transcript squid!
Jiunn-Yuan Lin 林俊源
Institute of Physics 交大物理所
National Chiao Tung University
Contents
Introduction to magnetism
Introduction to superconductivity
The best way of measuring the magnetic
moment-SQUID!
Specification of MPMS
Fundamentals of magnetism
Diamagnetism
Paramagnetism
Ferromagnetism
Antiferromagnetism
Diamagnetism
Due
to Faraday’s law
dB
E
dt
B B dA
Paramagnetism
M
B
C
T
C
T
Ferromagnetism
Antiferromagnetism
Hysteresis
Magnetic domains
To minimized the
magnetostatic energy
U
1
2
2
B dx
0
3
Magnetic Force Microscope (MFM)
Introduction to superconductivity
The Race to Beat Cuprates?
Hg - cuprate
TI - cuprate
150
100
?
Tc(K)
YBCO
Fe-based
superconductors
Cuprates
MgB2
LSCO
50
Nb3Ge
e-doped SmOFe
e-doped LaOFeA
e-doped LaOFeP
Metallic alloys
0
70
80
90
100
110
Year of discovery
The crusade of Room Temperature superconductors?
Josephson effect
(1962)
The
electronic
superconductors
applications
of
Speed(sec/gate)
Thermal limit
Quantum
limit
SC device
Power consumption
Speed & power consumption of SFQ device
SQUID
The SQUID
Within
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 Control
Patented dual impedance design allows continuous
operation below 4.2 K
Sample tube thermometry improves temperature
accuracy and control
Transition 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:
Operation Below 4.2 K:
Temperature Stability:
Sweep Rate Range:
1.9 - 400 K (800 K with optional oven)
Continuous
±0.5%
0.01 - 10 K/min with smooth transitions
through 4.2 K
Temperature 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
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
measurements
Magnets have two operating resolutions: standard and high
resolution
Type of Magnet
1 tesla
5 tesla
7 tesla
Standard resolution
0.5 Oe 1.0 tesla
1 Oe 5.0 tesla
2 Oe 7.0 tesla
High resolution
0.05 Oe 1500 Oe
0.1 Oe 5000 Oe
0.2 Oe 6000 Oe
Hysteresis Measurement
Reciprocating Sample Measurement System
(RSO)
Improved measurement sensitivity
Increased measurement speed
No waiting for the SQUID to stabilize
Very fast hysteresis loops up to 8x faster than conventional
MPMS
Servo motor powered sample transport allows
precision oscillating sample motion
High 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 Data
This measurement
takes ~ 3.5 hours in
persistent mode
Reciprocating Sample Measurement System
(RSO)
Frequency Range:
0.5 - 4 Hz
Oscillation Amplitude: 0.5 - 50 mm
Relative 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)
0.0005
Ba(Fe1-xCox)2As2 (x=0.08) H//ab=50 Oe
FC
ZFC
0.0000
M (emu)
-0.0005
-0.0010
-0.0015
-0.0020
0
5
10
15
T (K)
20
25
30
MPMS System Options
Transverse Moment Detection
for examining anisotropic effects
Second SQUID detection system
Ultra-Low Field
Reduce remanent magnet field to
±0.05 Oe
Extended Dynamic Range
External Device Control
Control user instruments with the
MPMS
10 kBar Pressure Cell
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
Measure moments to ±300 emu
Sample Rotators
Vertical and Horizontal
SQUID AC Susceptibility
2 x 10-8 emu sensitivity 0.1 Hz to
1 kHz
Liquid Nitrogen Shielded Dewar
EverCool Cryocooled Dewar
No-Loss liquid helium dewar
No helium transfers
SQUID AC Susceptibility
Dynamic 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 systems
Requires system to be returned to factory for upgrade
SQUID AC Susceptibility
Features
Programmable Waveform Synthesizer and high-speed Analogto-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 sensitivity
Specifications
Sensitivity (0.1 Hz to 1 kHz):2 x 10-8 emu @ 0 Tesla
1 x 10-7 emu @ 7 Tesla
AC Frequency Range:
AC Field Range:
DC Applied Field:
0.01 Hz to 1 kHz
0.0001 to 3 Oe (system dependent)
±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 achievable
Custom-designed fluxgate magnetometer supplied
Includes Magnet Reset
Requires 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 Oven
Provides 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 steps
Sample 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 connector
Use 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 electronics
Use with Manual Insertion Utility Probe for
automated electro-transport measurements
MPMS MultiVu version written in Borland’s Delphi
(Visual Pascal) programming language
Fiber Optic Sample Holder
Allows sample to be illuminated by an external light
source while making magnetic measurements
Optimized for near UV spectrum (180 to 700 nm)
Includes 2-meter fiber optic bundle
Sample bucket 1.6 mm diameter and 1.6 mm deep
SMA connector
Slide seal
Fiber optic bundle