| Stan Zurek, Magnetic properties, Encyclopedia Magnetica,
Magnetic properties - a collective term referring to various magnetic parameters measurable or attributed to various quantities of magnetic materials.
Typical magnetic properties important from a technical and application viewpoint are:
- magnetic saturation Jsat or Msat
- coercivity Hc (for magnetically hard materials BHc and JHc)
- remanence Br
- energy density BHmax (for permanent magnets)
- Barkhausen noise activity
- magnetic domain activity
But this list is not exhaustive as different magnetic quantities are required for different applications, and there can be a very strong relationship between magnetic and other parameters such as mechanical strength, eddy current loss, ease of manufacturing, cost, etc.
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Measurement of magnetic properties
Magnetic properties are measured by applying suitable electromagnetic, mechanical, thermal, or other excitation and measuring the response of the material under test. A widely applied method is to measure a family of B-H loops (also referred to as hysteresis loops), by applying known magnetic field strength H and measuring the response of the material in the form of magnetic flux density B.
Ferromagnetic and ferrimagnetic materials are of high practical importance for energy conversion. They behave quasi-linearly at low excitation, but always exhibit magnetic saturation at high excitation. This non-linear behaviour can be quantified from the B-H loops, which also allow measuring permeability (slope of the B-H curve), loss (area of the loop), saturation (maximum value of achievable response), coercivity (H at B=0), remanence (B at H=0), etc.
The number of magnetic properties that can be extracted from such measurement depends on the type of employed measurement apparatus, type of excitation, measurement technology, sensitivity of the test equipment, and so on.
Energy of permanent magnets can be tested by measuring magnetic dipole moment by using Helmholtz coil and the magnet withdrawal method. Magnetic moment can be measured also by the vibrating sample magnetometer or vibrating coil magnetometer.4) These devices can be also used for investigation of magnetic properties of non-magnetic materials (those which do not exhibit strong magnetic response, such as diamagnets, paramagnets, antiferromagnets).5)
However, there are many different types of measurement equipment, with hundreds of possible implementations, so it is not possible to list all the devices. For example, measurement of magnetostriction under stress requires a sophisticated apparatus which can simultaneously apply electromagnetic and mechanical excitation, and at the same time measure the resulting strain.6)