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How to the Test Magnetic Flux Coercivity

Magnetic materials play a fundamental role within technologies of today and are used in devices such as loudspeakers, transformers and computer hard drives. Magnets that have a permanent north and south pole are known as ferromagnetic materials. The polarity of the magnet may be switched by applying an external magnetic field. The magnetic field needed to reduce the internal magnetic field of the magnet (magnetization) to zero is known as the coercive field (magnetic flux coercivity) and this can be measured using a vibrating sample magnetometer.

Things You'll Need

Vibrating sample magnetometer (VSM)
Vacuum grease
Toothpick

Instructions

- 1
  Remove the probe from the VSM. The probe is essentially a nonmagnetic stick which the sample can be attached to. Put a small amount of vacuum grease on the probe using the toothpick. Place the sample on the probe and ensure it sticks well.
- 2
  Place the probe back into the VSM. A VSM basically consists of a pair of electromagnetic coils, which are sensitive to changing magnetic fields. As the sample magnetization changes, the induced voltage in the coils also change, and this is measured using a sensitive voltmeter.
- 3
  Monitor the coil voltage. The coil voltage varies depending on the sample position. In order to obtain the best data, the probe height should be varied while watching the coil voltage. Find the probe height that gives the maximum voltage signal.
- 4
  Select the field range. The measurement applies a magnetic field to the sample. Depending on the sample characteristics, this field range needs to be chosen. If unsure, consult the manufacturer of the magnetic material.
- 5
  Start the VSM. The field will vary while the induced coil voltage is varied. This leads to a curve known as a hysteresis loop. Once the curve has been generated, the coercivity can be determine by checking the point where the sample magnetisation crosses through zero.

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