The filters are being applied...

(Ferro) magnetism

Back in ancient times, people discovered that magnetite crystals attract or repel each other depending on their orientation. This physical phenomenon is referred to as magnetism. The words magnetite and magnesium are both derived from Magnesia, the name of an area in the Thessaly region of Greece where magnetic stone can be found in abundance.Magnetic separation

It is the iron in the rock that is responsible for the magnetic properties of magnetite. Many iron alloys possess magnetic properties. In addition to iron, we find magnetic properties in nickel, cobalt and gadolinium as well.

Although ferromagnetic (and ferrimagnetic) materials are the only kinds with strong enough magnetic properties to be drawn to a magnet (which is why they are called ‘magnetic’), all other substances also respond weakly to a magnetic field, via one or more other types of magnetism.

Ferromagnetic materials can be divided into magnetically 'soft' materials, such as annealed iron, which can be magnetized but usually do not retain the magnetization indefinitely, and magnetically 'hard' materials that do remain magnetized. Permanent magnets are made of 'hard' ferromagnetic materials such as Alnico and ferrite, which undergo special processing in a powerful magnetic field during production to 'align' their internal microcrystalline structure, making them very resistant to demagnetization.

Objects which strongly exhibit this behaviour are called magnets. There are natural and man-made magnets (e.g. Alnico, Fernico, ferrites). All magnets have two poles, which are referred to as the north pole and the south pole. The north pole of a magnet repels the north pole of other magnets and attracts the south pole of other magnets. Two south poles also repel.

Magnetism Gripper

Because the earth has a magnetic field as well, with its magnetic south pole close to the geographic north pole and its magnetic north pole close to the geographic south pole, a free-spinning magnet will always take on a north-south orientation. The names of the poles of a magnet are derived from this phenomenon. For the sake of convenience, but nevertheless slightly confusing, the south pole of “the 'earth magnet' is called the magnetic north pole and the north pole of the 'earth magnet' is called the magnetic south pole.

Magnetic field - North and South pole

A related phenomenon is electromagnetism, which is magnetism generated by an electric current. In essence, all magnetism is caused by either rotating or revolving electrical charges in eddy currents.

electromagnetism

Read more

Curieova teplota

Curieova teplota je pojmenována podle Pierra Curie (1859-1906).

magnetismus Curieova teplota

Curieova teplota je teplota, nad kterou feromagnetické materiály ztrácení jejich permanentní magnetické pole; magnetismus zcela zmizí.

Nad touto teplotou se materiál chová paramagneticky. Když teplota roste, molekulární excitace postupně narušuje vyrovnání rotace. Když je dosažena Curieova teplota, vyrovnání se zhroutí, protože tepelná energie překročila energii magnetické interakce.

Je obtížné Curieovu teplotu přesně změřit. Jednak permanentní magnetické pole kolem materiálu částečně zmizí. A za druhé se Curieova teplota značně liší i na základě malých množství nečistot v materiálu.

Například, pokud se magnet AlNiCo zahřeje nad svou Curieovu teplotu 850 °C, nebude již feromagnetický. Následně se stane paramagnetickým. Jakmile se magnet znovu ochladí, permanentní magnetické pole se nevrátí. Bude se však jednat o nová magnetická pole v malých oblastech v materiálu, tzv. Weissovy domény (Weiss 1865-1904), ale tato pole jsou zarovnána v náhodném směru, takže jejich vektorový součet nemá za následek vnější magnetické pole. Je však možné magnet znovu zmagnetizovat.

Feromagnetické prvky a slitiny s jejich Curieovými teplotami:

Materiál Curieova tepl.
Fe 770 °C
Co 1115 °C
Ni 354 °C
Gd 19 °C
AlNiCo 850 °C
Ferit 450 °C
Sm Kobalt 750-825 °C
Nd-Fe-B 310-340 °C

Magnet materials

Ferrite
magnets
 

Ferrite magnets Read more

Neodymium (Neoflux®) magnets

Neodymium Neoflux Magneten Read more

Samarium-cobalt magnets
 

Samarium Kobalt magneten Read more

Aluminum-nickel-cobalt magnets

Aluminum-nickel-cobalt magnets Read more

Plastic bonded magnets
 

Plastic bonded magnets Read more