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What is Superconducting Quantum Interface Device
(SQUID)?
SQUID magnetometer is one of the most effective and
sensitive ways of measuring magnetic properties. In particular, it is the
only method which allows to directly determine the
overall magnetic moment of a sample in absolute units.
The superconducting quantum interference device (SQUID)
consists of two superconductors separated by thin insulating layers to form
two parallel Josephson
junctions. The device may be configured as a magnetometer to
detect incredibly small magnetic fields small enough to measure
the magnetic fields in living organisms. Squids have been used to measure
the magnetic fields in mouse brains to test whether there might be enough
magnetism to attribute their navigational ability to an internal compass.
By Brian David Josephson in 1962, the
electrical current density through a weak electric contact between two
superconductors depends on the phase difference Δφ
of the two superconducting wave functions. Moreover, the time derivative of
Δφ is correlated with the voltage
across this weak contact. In a superconducting ring with one (so-called rf SQUID) or two (dc
SQUID, fig. 1, blue) weak contacts, Δφ
is additionally influenced by the magnetic flux Φ through this ring.
Therefore, such a structure can be used to convert magnetic flux into an
electrical voltage. This is the
basic working principle of a SQUID magnetometer.
When the sample is moved up and down it produces
an alternating magnetic flux in the pick-up coil .The magnetic signal of
the sample is obtained via a Superconducting pick-up coil
with 4 windings (fig. 3). This coil is, together with a SQUID antenna (red
in fig. 1), part of a whole superconducting circuit transferring the
magnetic flux from the sample to an rf SQUID
device which is located away from the sample in the liquid helium bath.
This device acts as a magnetic flux-to-voltage converter (blue in fig. 2).
This voltage is then amplified and read out by the magnetometer’s
electronics (green in fig. 2).
Cryocooler Compressor: The
MPMS EverCool system features an integrated cryocooler–Dewar System that recondenses
the He directly with in the EverCool Dewar.
Oven: For
high temperature measurement 300K
-800K
Sample
Rod: This is expensive
>$180, if the rod is bent the straw could be lost in side the
Dewar.
UPS: An
uninterruptible power supply (UPS), also known as a continuous power supply
(CPS) or a battery backup is a device which maintains a continuous supply
of electric power to connected equipment by supplying power from a separate
source when utility power is not available.
Note: Please
note that user must be on time and be ready with the sequence before
loading the sample
System
Specification:
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DESCRIPTION
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MPMS
XL7
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Field Range
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± 7.0 Tesla(70,000 Gauss)
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Field Stability
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1ppm/hour
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Intrinsic Field Uniformity
(4cm:_2cm from center of pickup coil)
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0.01% over 4cm
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Field setting resolution
(Gauss)
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2 G to 70,000 G
0.2 G to 6,000 G
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Residual field
(Gauss)
Oscillate
Mode
No
Overshoot Mode
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<5 G typical
<30 G typical
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Maximum Calibrated Sample Size(Sample Chamber
ID)
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9mm
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RSO Measurement
Differential sensitivity (minimum resolvable
change in magnetic moment, 1E-4 EMU range)
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<1E-8 EMU to 2,500 Oe
£6E-7
EMU to 7 Tesla (STD. ERROR)
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Range of measurement
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±5.0 EMU
(option to ± 300
EMU)
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Temperature range at the sample space (Kelvin)
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1.9 K to 330 K Option to 800 K
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Temperature calibration accuracy at the sample
space
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± 0.5% typical
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Temperature stability at the sample space (Kelvin)
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± 0.5%
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Temperature spatial variation in sample chamber
(Kelvin)
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±0.1 K over 8cm
±1.0 K over 15cm
@235 K
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Rate of temperature change (max.)
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300 K to 10 K @ 10 K/min
10 K to 2 K @ 2 K/min
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Helium capacity (Liters)
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56
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Helium usage* Standard Super Insulated Dewar (Liters/day)
Optional Nitrogen Jacketed Dewar (Liters/day)
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6
4.5
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Some
Useful Links: http://www.qdusa.com/
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