Magnetic Properties: A Guide to Key Specifications

Understanding the technical specifications of magnets starts with a few basic magnetic concepts. Here are some key properties and what they mean:

Remanence (Br)

Remanence, or residual flux density, is the magnetic flux density remaining after the magnetising field has been removed. It is one of the main characteristics used to describe a permanent magnet. It is measured in teslas (T) or gauss (G).

Coercivity (Hc)

Coercivity describes the reverse magnetic field strength needed to reduce a specified magnetic quantity to zero. Normal coercivity (HcB) refers to magnetic flux density, while intrinsic coercivity (HcJ) refers to magnetic polarisation. It helps indicate resistance to demagnetisation. Units include amperes per metre (A/m) and oersted (Oe).

Maximum Energy Product (BHmax)

The maximum energy product is the largest value of the product of magnetic flux density and field strength on the demagnetisation curve. It describes the energy capability of a magnetic material and is commonly given in kilojoules per cubic metre (kJ/m³) or megagauss-oersteds (MGOe). A higher value generally allows a more compact magnet for a comparable magnetic circuit.

Operating Temperature

Magnet performance changes with temperature. The operating temperature range indicates the conditions in which a magnet can be used without unacceptable deterioration of its magnetic properties. Grades such as N, M, H, SH, UH and EH have different maximum operating temperatures; the actual limit also depends on the magnet's geometry and magnetic circuit.

Magnetic Polarisation (J)

Magnetic polarisation describes the contribution of the material's magnetisation to magnetic flux density. It is closely related to remanence and is expressed in teslas (T). Magnetisation itself is expressed in amperes per metre (A/m).

These magnetic characteristics are essential when selecting magnets and designing their applications. Understanding them helps you choose a suitable magnet type for industrial, technical and research uses.