Magnetic susceptibility
The magnetic susceptibility ( from Lat susceptibilitas " takeover capability") is a physical quantity that indicates the magnetization of matter in an external magnetic field. In the simplest case it is a proportionality constant determined by the ratio of magnetization to magnetic field strength. In general, it is a function, which may depend on a number of variables - in particular of the location of the frequency of the magnetic field and the previous magnetization. The values range from -1 to almost infinite, where negative values indicate a magnetization against the external magnetic field.
A similar connection between polarization and electric field is called the ( di - ) electric susceptibility. The magnetic susceptibility is also closely related to the magnetic permeability.
- 3.1 constant magnetic susceptibility
- 3.2 materials with a magnetic order
Definition
The most common form, the volume magnetic susceptibility ( is the Greek letter chi, for magnetic - often, or simply ), in the simplest case describes a proportionality constant, defined by the ratio: of magnetization and magnetic field strength. As the size ratio susceptibility is unitless.
This definition is only correct insofar as magnetic field strength and magnetization have a simple linear relationship. In general the combined magnetic susceptibility as a derivation
Defining, that is, the change of the magnetization change in the magnetic field strength. The subscripts denote the components of the spatial orientation ( in Cartesian coordinates ) of the respective fields. In this form, the susceptibility tensor quantities and taken into account, can that magnetization and magnetic field pointing in different directions (magnetic anisotropy ).
With related variables
Molar mass susceptibility and
Two other measures of magnetic susceptibility are used, the magnetic mass susceptibility and molar magnetic susceptibility. The mass susceptibility ( or also (!) ) Refers to the susceptibility density per
Measured in m3 · kg -1. The molar susceptibility differs by using the molar mass
And is measured in m3 · mol -1.
Magnetic permeability
The constant magnetic susceptibility is a simple relationship to the relative magnetic permeability:
This results from the dependence of the magnetic flux density B of the magnetization M and the magnetic field strength H:
Is the magnetic field constant.
Conversion between SI and CGS units
All of the above definition refers to that prescribed in Germany SI. Since the permeability of the vacuum is defined differently in Gaussian CGS system, resulting in a conversion factor of 4π with respect to the SI:
Since the (volume ) susceptibility is unitless in the CGS system, care must be taken when using older table values on the unit system used in particular. For example, the susceptibility of 20 ° C warm water -7.19 · 10-7 in the CGS system, which corresponds to a value of -9.04 · 10-6 in the SI.
Classification of magnetic materials
Constant magnetic susceptibility
All the substances react to some degree to magnetic fields. In the simplest case a constant magnetic susceptibility two groups:
Dia - and paramagnetism occur in each aggregate state. Since these effects are very small, as a rule, many substances are reported as " non-magnetic ".
Materials with a magnetic order
Solid with a magnetic order speak very strongly to magnetic fields. Their magnetic susceptibility shows a complicated behavior. Above a threshold temperature it behaves paramagnetic, below it depends on other factors:
Ferri- and ferromagnetic materials can be used as the permanent magnet when after switching off the external magnetic field having a large residual magnetization. Soft Magnetic Materials can be, however, very simple ( re) magnetize and are therefore used, for example, generators and transformers.
Calculation of the susceptibility by the Gouyschen scale
To Gouy- balance see magnetochemistry.
By introduction of a paramagnetic or diamagnetic substance in a magnetic field, the field lines are drawn together or spread apart. For the magnetic field, the following relationship applies:
Two forces can be determined with the measurement by a Gouysche scale: Changing the gravity and the magnetic force change. Both forces must be identical in equilibrium. The force of gravity acting on the scale is the product of mass change multiplied by the acceleration due to gravity:
The magnetic field change by the introduction of a paramagnetic or diamagnetic substances in the magnetic field is given by:
Where A is the area of the substance to be examined which is permeated by the magnetic field, and H is the magnetizing field.
Out of balance and resolution by
Can the volume susceptibility are determined.
From the above relationship, the magnetizing field H = B are / intended for the vacuum. For a neodymium magnet with a magnetic flux density of 0.29 Tesla, for example, a magnetic field strength of 230 781 A / m or 2899 Oe results directly on the surface of a pole. The magnetizing field is the same as the magnetic field depends on position and distance from the current-carrying conductor or a magnet and can be determined by (circular ) integral calculus exactly.