connection between the magnetic field (H) and magnetic induction (B) into the material is characterized by a physical quantity called magnetic permeability . absolute magnetic permeability environment - is the ratio of B to H. According to the International System of Units is measured in units called Henry to 1 meter.
its numeric value expressed by the ratio of its size to the size of the magnetic permeability of the vacuum and is denoted by μ.This value is called the relative magnetic permeability (or simply permeability) environment.As a relative, it has no units.
Consequently, the relative magnetic permeability μ - value showing the number of times in the induction field of the environment is less (or more) of the vacuum magnetic field induction.
When exposed to an external magnetic field the substance, it becomes magnetized.How does this happen?According to the hypothesis of Ampere, in every substance constantly circulating microscopic electrical currents caused by the movement of electrons in their orbits and the presence of their own magnetic moment.Under normal circumstances, this movement is disordered, and the field "quenched" (cancel) each other.When placing the body in an external field the current regulation, and the body becomes magnetized (ie. E. Having its field).
permeability of different substances.Based on the value thereof, subject matter division into three large groups.
have diamagnetics value of the magnetic permeability μ - a little less than one.For example, bismuth μ = 0,9998.For diamagnetic include zinc, lead, quartz, rock salt, copper, glass, hydrogen, benzene, water.
permeability of paramagnetic materials slightly larger units (for aluminum μ = 1,000023).Examples of paramagnetic materials - nickel, oxygen, tungsten, ebonite, platinum, nitrogen, air.
Finally, the third group belongs to a number of substances (mostly metals and alloys), whose magnetic permeability significantly (by several orders of magnitude) greater than one.These substances - ferromagnets.Basically here include nickel, iron, cobalt and their alloys.For steel μ = 8 ∙ 10 ^ 3, for the alloy of nickel and iron, μ = 2.5 ∙ 10 ^ 5.Ferromagnetic materials have properties that distinguish them from other substances.Firstly, they have a residual magnetism.Secondly, their permeability is a function of the induction of the external field.Thirdly, for each of them there is a certain threshold temperature, called the Curie point , in which he loses ferromagnetic properties and become paramagnetic.For nickel the Curie point - 360 ° C, for iron - 770 ° C.
properties of ferromagnets determines not only the permeability but also the value of I, called magnetization of the substance.This is a complex non-linear function of the magnetic induction, the growth of the magnetization is described by a line called the magnetization curve .At the same time, having reached a certain point, the magnetization is almost stops growing (magnetic saturation occurs ).Backlog value of the magnetization of a ferromagnet by increasing the value of the induction of the external field is called magnetic hysteresis .At the same time there is a dependence of the magnetic characteristics of the ferromagnetic not only on its state at the moment, but also on its previous magnetization.Graphical representation of the curve of the dependence of the hysteresis loop is called .
Due to its properties, ferromagnetic materials commonly used in the art.They are used in rotors of motors and generators, in the manufacture of transformer cores and electromagnetic relays, in the manufacture of components of electronic computers.The magnetic properties of ferromagnetic materials are used in tape recorders, telephones, magnetic tape and other media.
