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They also have high magnetic permeability. These so-called ceramic magnets are cheap, and are widely used in household products such as refrigerator magnets . The maximum magnetic field B is about 0.35 tesla and the magnetic field strength H is about 30–160 kiloampere turns per meter (400–2000 oersteds ). [ 33 ]
Mu-metal is a soft magnetic alloy with exceptionally high magnetic permeability. The high permeability of mu-metal provides a low reluctance path for magnetic flux , leading to its use in magnetic shields against static or slowly varying magnetic fields.
Magnetically hard materials have high coercivity, whereas magnetically soft materials have low coercivity. The overall strength of a magnet is measured by its magnetic moment or, alternatively, its total magnetic flux. The local strength of magnetism in a material is measured by its magnetization.
Different materials have different saturation levels. For example, high permeability iron alloys used in transformers reach magnetic saturation at 1.6–2.2 teslas (T), [4] whereas ferrites saturate at 0.2–0.5 T. [5] Some amorphous alloys saturate at 1.2–1.3 T. [6] Mu-metal saturates at around 0.8 T. [7] [8]
Permeability is influenced by the spacing between the grains, which form distributed air gap; the less gap, the higher permeability and the less-soft saturation. Due to large difference of densities, even a small amount of binder, weight-wise, can significantly increase the volume and therefore intergrain spacing.
Permeation can occur through most materials including metals, ceramics and polymers. However, the permeability of metals is much lower than that of ceramics and polymers due to their crystal structure and porosity. Permeation is something that must be considered carefully in many polymer applications, due to their high permeability.
The gray spheres are oxygen, green are divalent iron, blue are trivalent iron. Also shown are an iron atom in an octahedral space (light blue) and another in a tetrahedral space (gray). Magnetite is a mineral and one of the main iron ores , with the chemical formula Fe 2+ Fe 3+ 2 O 4 .
Permendur rods. Permendur is a cobalt-iron soft ferromagnetic alloy with equal parts of cobalt and iron which is notable for its high magnetic saturation level. [1] [2] Its saturation flux density of around 2.4 tesla is the highest of any commercially available metal.