Open, square, square magnet
Knowledge is introduced: the square magnet
Is that there is no additional magnetic field, square magnet can keep its own magnetic an object. According to different materials can keep ten years commonly, powerful magnets are available with a ferromagnetic materials, such as iron, nickel, etc. Magnet is a general term, is refers to has the magnetic, the actual component may not contain iron. Relatively pure iron itself has no strong magnetic metallic state, only near the square magnet magnetic induction, general square magnet inside and other impurity elements such as carbon to make magnetic stabilized, but it will reduce the electronic freedom and less prone to conduct electricity, so the current through the bulb light up, iron is a common magnetic elements, but many other elements have a stronger magnetic, as many square magnet is the mixture of neodymium, iron, boron, etc.
In addition, the material need to use the square magnet is made of high must have broad hysteresis loop, because of this, when the external magnetic field is zero, can still have relatively strong magnetization; If you want to change the magnetization into zero, will be expected to exert strong external magnetic field.