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Magnetization Measurements Wiki Draft Magnetization, also called magnetic polarization, is the measure of the magnetic field produced by a material. A material can become magnetized, or magnetically polarized, but things such as applying an external magnetic field or applying a physical stress. In Condensed matter physics, it is often necessary to measure the magnetization of a material. In order to accomplish this, one may use any of a variety of magnetometry techniques.

SQUID (Superconducting quantum interference device) (Insert Link to Squid Page) SQUID magnetometry is a very sensitive magnetometry technique. SQUID makes use of a superconducting path with one or more Josephson’s junction. SQUIDs can be designed in two different ways: DC SQUID or RF SQUID.

DC SQUID A DC SQUID makes use of superconducting path that splits so as to go through two Josephson’ junctions, and then returns to a single path. In operation an input current is applied to the single path that is split exactly in half between the two paths. In order to take a measurement, a small sample of material is magnetized such that a magnetic flux is produced through the loop made by the two paths. This magnetic flux creates second current flowing through the loop, which opposes the original current in one half of the loop, and Increases the current in the other. Once the critical current of the Josephson junction is reached a voltage difference is present across the Josephson junction. Due to the Quantization of magnetic flux from super currents, once the flux from the sample reaches half the magnetic flux quantum, the direction of the magnitude of the super current flowing through each of the two Josephson junctions switches, such is the case at every half integer of the magnetic flux quantum. RF SQUID A RF SQUID utilizes only one Josephson junction. This method makes use of the AC Josephson effect. It is less sensitive that the DC SQUID but it is cheaper to manufacture. Inductive Pickup Coils Other methods of measuring magnetization make use of inductive pickup coils. VSM (Vibrating Sample Magnetometer) (Insert Link to VSM page) VSM is one technique that makes use of Inductive pickup coils. In order to take a measurement utilizing this method, a sample is magnetized by placing it in a constant magnetic field. The sample is then physically vibrated so as to create a change of flux through the pickup coils. The current induced in the pickup coils can be measured. Then the magnetization of the sample can be easily calculated.

Pulsed Field Extraction Magnetometry (PFEM) Pulsed Field Extraction Magnetometry is another method making use of pickup coils to measure magnetization. Unlike in the case of VSM where the sample is physically moved in PFEM the sample is secured, and the external magnetic field is changed rapidly, or pulsed. One of multiple techniques must then be used to subtract the external field from the field produced by the sample.

Standard AC Magnetometry In this method, which is the least sensitive, two coils are used, a driving coil, and a pickup coil. The driving coil is used to create and AC magnetic field magnetizing the sample. The pickup coil is used as before. In this method as in PFEM, it is necessary to make use of a technique to cancel out the driving field.