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Introduction to the NHMFL Pulsed Field Facility at LANL

Information on the physical set-up of pulsed field measurements

Read about lock-in amplifiers and their role in your measurements

Information about noise and ways to eliminate it from your measurements

How to collect and evaluate your measurement data

Information on optical spectroscopy

Information about time-resolved optics

Information on de Haas van Alphen Effect measurements

Information on Shubinkov de Haas Effect measurements

Information on Absolute Resistivity measurements

Information on Heat Capacity measurements

Information on RF Penetration Depth measurements

Sample Preparation


  GENERAL RESISTIVITY MEASUREMENTS:

Before pulsed field measurements can be taken, a sample must be prepared and attached to the probe. This process includes the placement of leads that will carry the signal from the sample. Further, the sample must be securely connected to the probe so that it does not move during the magnetic field pulse.

First, appropriate leads must be attached to your sample depending on what type of measurements will be taken. For most experiments, attach four leads to the sample: two to carry the current and two to measure the voltage. If desired, two additional leads can be added to measure Hall resistance, making a total of six leads. It is common to use 1 mil gold wire to construct leads, however many other types are acceptable. These leads are attached with a variety of things, including epoxy and gold, graphite or silver paste, depending on the sample.

Once leads are in place, the sample can be placed on a 2 mm x 2 mm x .5 mm (approximately) piece of sapphire. Sapphire is used because it has high conductivity, but is also well insulated. Some glue is necessary to hold the sample in place such as GE varnish or Duco cement.

Finally, the sample is attached to the probe using a variety of methods. Some samples are first placed in a removable socket to hold the sample in place on the probe while other samples can be placed directly on the probe.

GENERAL MAGNETIZATION MEASUREMENTS:

For investigations involving the de Haas-van Alphen Effect, the sample is placed directly inside the pick-up coils (without leads attached), or occasionally on the end of the coils. In order to fit inside the coils (whereupon the best signal-to-noise is obtained), the sample must be able to fit inside a hole with a diameter of 400 microns (2-3 mm long). Small amounts of silicon-based vacuum grease are used to prevent the sample from moving during the pulse.

In the case of magnetization measurements, it is important for the sample to be moved in and out of the coils (in-situ) between pulses. For this reason, the pick-up coils are made larger in order to accommodate a capsule that contains the sample. The internal diameter of the capsule is approximately 900 microns (2 mm long).