Research Equipment
SQUID System
The following is a description of a magnetization measurement system using the Superconducting QUantum Interference Device (SQUID).
What kind of device is the SQUID?
SQUID is an acronym for "Superconducting QUantum Interference Device." It is a device capable of detecting minute changes of magnetic flux.
When two superconductors with different phases of the superconducting order parameters are connected through a weak link (Josephson Junction),
tunneling current can flow between them. The tunneling current reaches minimum values at points where the applied magnetic flux is an integral
multiple of the flux quantum. This behavior is called the Fraunhofer-type quantum interference effect. The Fraunhofer effect is caused by the
Josephson effect. A device formed by a superconducting loop with one or more Josephson Junctions is called a SQUID.
There are two types of SQUID, the dc-SQUID and rf-SQUID. The device used in the SQUID system at JAIST is an rf-SQUID with a single Josephson
Junction. The magnetic flux in the SQUID changes as a unit of Φ0, when the magnetic flux around the SQUID is changed by a change of
magnetization in the measured sample. The magnetization of the sample can be measured by detection of this change of the magnetic flux. Φ0 is equal to 2.07x10-7 Gauss cm which is very small. So, it is possible to measure extremely small amounts of magnetization. The SQUID system at
JAIST is for measuring magnetization, but SQUID is also used in other fields such as medical service (for example, SQUID-CT).
A standard material for SQUID is niobium (Nb) today, though a SQUID using oxide superconductors has recently been developed. Because niobium makes
phase transition to the superconducting state at 9.2K, liquid helium must be used for operating the SQUID device.
Where was this device manufactured?
The SQUID system was manufactured by a US company called Quantum Design. It is a very user-friendly measurement system and is currently being used in many universities and research institutions worldwide.
What are the SQUID's capabilities in more specific terms?
Measurement accuracy in the system is on the order of 10-8 emu, and it can easily measure superconducting diamagnetizations in a sample of 100 μg. A magnetic field of up to ±7.0 Tesla can be applied to the sample. Measurements can be taken for magnetic field dependence at constant temperatures, temperature dependence at constant magnetic fields, and angular dependence at constant temperatures and constant magnetic fields. The system is entirely computer-controlled. Measurement can be performed automatically when used together with measurement programs.
How is it being used at JAIST?
It is primarily used by researchers at the School of Materials Science to investigate such things as the magnetic properties of magnetic
materials, and the physical properties of superconductors. It's in operation all year, and is used by many researchers.
