The magnetic properties of metals are influenced by temperature. Among all metals only iron, nickel and cobalt show ferromagnetic properties at room temperature.
The rise of temperature causes ferromagnets to lose their magnetic susceptibility. When the temperature reaches a certain value, the ferromagnetic material becomes a paramagnetic one. This value is called the Curie Temperature of a metal.
The magnetic permeability of ferromagnetic metals depends on the intensity of the external magnetic field. When such a field is removed, ferromagnets still display residual magnetism. By means of this force, permanent magnets attract or repel other metals or magnets.
A magnetized ferromagnetic alloy still exhibits residual magnetism, which wends the same direction as the field did. Demagnetization requires an oppositely oriented field of a certain strength, called coercion. If this field is stronger than said strength, the alloy gets magnetized -directed the opposite way then the field.
Each remagnetization involves irreversible dissipation of energy that’s called hysteresis energy loss.
Magnetically soft nickel alloys – properties
●High initial permeability µ ●High max relative permeability ●Constant permeability in changing temperatures ●High saturation magnetostriction ●An immediate reaction to the magnetic field's change ●Low Curie Temperature ●High resistivity ●Low eddy-current loss in alternating flux ●Narrow hysteresis loop (magnetization – demagnetization loop) ●Low hysteresis-energy loss
Shortly put- magnetically soft alloys are easy to magnetize, demagnetize and remagnetize.
●Nickel-containing magnetically soft alloys are used extensively in a variety of applications, including: ●Audio-related transformers ●Magnetic amplifiers ●Transducers ●Radar pulse transformers ●Synchronous motors and torque motors ●Loading coils ●Radiofrequency shields (RF shields) ●Temperature compensators
Permalloy is a unique magnetically soft alloy. Its feature is an almost rectangular shape of the hysteresis loop and two remanence values.
Magnetically soft amorphous metals
Amorphous metals (metallic glass) are characterized by high resistance, following low hysteresis loss and the ability to work at high frequencies.
Magnetically hard nickel-containing alloys
Magnetically hard alloys are used to produce permanent magnets that exhibit strong residual magnetism and aren’t easy to demagnetize and remagnetize.
Alnico alloys are used to craft permanent magnets.
