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SQUID
Our SQUID (Superconducting Quantum Interference Device) can measure the DC susceptibility of samples up to applied fields of 7 T. This is also heavily used to characterize the magnetic properties of the materials that we synthesize..
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Muon Spin Relaxation
Muon Spin Relaxation (µSR) is a sensitive local probe of spin statics and dynamics in materials.
- µSR stands for muon spin rotation, relaxation, resonance, research etc. The name was chosen to give an analogy to NMR.
- Muons, which are subatomic particles of the lepton family, are injected into materials one at a time, and we watch their subsequent decay into positrons and neutrinos.
- By monitoring the polarization of the muon as a function of time, we can get information of the local spin environment at each muon site.
- Excellent probe for magnetism, superconductivity, chemical reactions, semiconductor physics, etc.
- Some of this technique was pioneered in Canada, by Canadians!
Creation of muons through high-energy collisions: (courtesy of J. Sonier)
There are basically two steps in this technique: the creation of muons, and the detection of the decay products of the muons:
Step one:
Pion production via collisions with protons and a target (whose subsequent decay yields 100% spin polarized muons). Since the muon is charged (and last on the order of microseconds), we can create muon beams for our experiments
A schematic of a typical muon spin relaxation experiment
Step two:
Decay of muon inside of material (governed by weak interaction – positrons are preferentially emitted in direction of muon spin). The only reason why this technique works is because of the weak interaction!
The detector array around a sample in a typical muon spin relaxation measurement
The following animations illustrate this technique in flashy detail! (courtesy of A. Savici)
We complete most of our experiments at TRIUMF in lovely Vancouver, British Columbia.
- There are different ways to do µSR depending on how you orient the applied field – zero field, longitudinal field (along the spin polarization), and transverse field (perpendicular to the initial spin polarization)
- ZF µSR – weak magnetism, search for magnetic ordering
- LF µSR – spin dynamics (different time scales than neutron scattering)
- TF µSR – Knight shift measurements, penetration depth (superconductivity)
Since muon spin relaxation can probe different time scales than neutron scattering, it is often used in combination with other techniques to give a more complete picture of the dynamics within a solid.
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