Soft Magnets

     Soft magnetic materials are those materials that are easily magnetised and demagnetised. They typically have intrinsic coercivity less than 1000 A/m. They are used primarily to enhance and/or channel the flux produced by an electric current. The main parameter, often used as a figure of merit for soft magnetic materials, is the relative permeability ( mr, where mr = B/moH), which is a measure of how readily the material responds to the applied magnetic field. The other main parameters of interest are the coercivity, the saturation magnetisation and the electrical conductivity.


                                            Soft Magnetic Materials

     Characteristics
     Low Hc( Coercive Force) and high magnetic conductivity
     Easy to magnetise and demagnetise
     low saturated flux density
     low magnetic conductivity
     low Curie temperature
     low mid-frequency loss

                                           Soft Ferrite Magnets

     The types of applications for soft magnetic materials fall into two main categories: AC and DC. br />      In DC applications the material is magnetised in order to perform an operation and then demagnetised at the conclusion of the operation, e.g. an electromagnet on a crane at a scrap yard will be switched on to attract the scrap steel and then switched off to drop the steel.
     For DC applications the main consideration for material selection is most likely to be the permeability. This would be the case, for example, in shielding applications where the flux must be channelled through the material. Where the material is used to generate a magnetic field or to create a force then the saturation magnetisation may also be significant.
     In AC applications the material will be continuously cycled from being magnetised in one direction to the other, throughout the period of operation, e.g. a power supply transformer. A high permeability will be desirable for each type of application but the significance of the other properties varies.
     For AC applications the important consideration is how much energy is lost in the system as the material is cycled around its hysteresis loop.

                                           Rubber Magnets