To the list of lectures

§ 2 Dia-and paramagnetic

Diamagnetic are those substances which have a magnetic moment of the atom in the absence of an external magnetic field is zero.



When an external magnetic field is placed a substance, all the atoms of the material are in a magnetic field that changes the motion of electrons in the atom, so that an additional current, similar to the induction current. If the vector  and  form an angle α, then in a magnetic field  electron orbit will rotate around the direction  with some angular velocity ( - Larmor precession frequency). Such movement mechanics called precession.

The precession of the electron orbit is equivalent to an additional electron motion around the magnetic field in addition to rotation around its axis of rotation and orbit. This extra electron motion in the magnetic field leads to a vicious induced current, which has a magnetic moment, which is always directed against the field. Thus, the cause of the additional magnetic moments - the precession of the orbit of the electron.

Since diamagnetics magnetized opposite to the magnetic field, their magnetization is negative.

For diamagnetic include metals Bi, Ag, Au, Cu; water, glass, inert gases, etc.

Diamagnetism is common to all substances, but a number of substances diamagnetic effect is blocked as stronger effects.

Paramagnetic called substances in which the atoms in the absence of an external magnetic field have some permanent magnetic moment

pmat .

However, due to thermal motion of the magnetic moments are oriented randomly, so .

When a magnetic field, forces that guide the magnetic moments of each atom. The magnetic moments of trying to line up on the field. Thus, the paramagnetic magnetized, creating its own magnetic field collinear with the external field and reinforcing it.

The process of the magnetic moments of the atoms in a magnetic field is called the paramagnetic effect.

Arrayed in paramagnetic forces are relatively small compared with the forces of thermal motion, to break down the ordering. Therefore, with decreasing temperature paramagnetic susceptibility usually increases.

Paramagnetic to include rare earth metals, Pt, Al, Mg, Cr, O2 etc.


§3 A magnetic field in the material.

Magnetic susceptibility and permeability

The current flowing through a conductor is called macrocurrent. The magnetic field generated by these currents, called the field of macrocurrent and denote macrocurrents. If an object is placed in this field , then the magnetic moments of the atoms of matter will be oriented against the field in the diamagnetic and paramagnetic in the field. Ie microcurrents substances create an internal field ,opposite directions in the diamagnetic and paramagnetic in collinear. Then the magnetic induction vector of the resultant magnetic field in matter is equal to the vector sum of the magnetic induction of the external field and microcurrents field


where .

If we consider the matter in any section of a cylinder perpendicular to its axis, the substance inside the molecular currents of neighboring atoms are directed towards each other and cancel each other out. Not be compensated only molecular currents on the side of the cylinder. The current through the cylinder surface is similar to the current in the solenoid, and creates within it the field

;             N = 1; µ = 1,


Experience shows that in weak magnetic fields, the magnetization is proportional to the field intensity , causing the magnetization

[χ] = 1

where χ - a dimensionless quantity called the magnetic susceptibility shows how the substance reacts (magnetized) to an external field .


-link permeability μ and susceptibility χ.

Magnetic permeability shows how many times the resulting magnetic field in a substance greater than the external magnetizing field macrocurrents .


For diamagnetic:

χ  < 0;  µ < 1;

χ ~ 10-5 ÷ 10-7.






For paramagnetic:


χ > 0;  µ > 1;

χ ~ 10-3 ÷ 10-5.



To the list of lectures