Faraday balance
Encyclopedia
A Faraday balance is a device for measuring magnetic susceptibility
. Magnetic susceptibility is related to the force experienced by a substance in a magnetic field
. Various practical devices are available for the measurement of susceptibility, which differ in the shape of the magnetic field and the way the force is measured.
In the Gouy balance there is a homogeneous field in the central region between two (flat) poles of a permanent magnet, or an electromagnet. The sample, in the form of a powder in a cylindrical tube, is suspended in such a way the one end lies in the centre of the field and the other is effectively outside the magnetic field. Errors due to inefficient packing in the sample tube are difficult to eliminate.
In the Faraday balance the field is inhomogeneous. The pole pieces of the magnet are so shaped that there is a region in which the product of the field strength and field gradient in the z direction is constant. The sample is placed in this region. The force in this case is independent of the packing of the sample and depends only on the total mass of the material present. The method is sensitive and highly reproducible and can be applied to single crystals. The force is measured as a weight change, using a torsion balance.
Magnetic susceptibility
In electromagnetism, the magnetic susceptibility \chi_m is a dimensionless proportionality constant that indicates the degree of magnetization of a material in response to an applied magnetic field...
. Magnetic susceptibility is related to the force experienced by a substance in a magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
. Various practical devices are available for the measurement of susceptibility, which differ in the shape of the magnetic field and the way the force is measured.
In the Gouy balance there is a homogeneous field in the central region between two (flat) poles of a permanent magnet, or an electromagnet. The sample, in the form of a powder in a cylindrical tube, is suspended in such a way the one end lies in the centre of the field and the other is effectively outside the magnetic field. Errors due to inefficient packing in the sample tube are difficult to eliminate.
In the Faraday balance the field is inhomogeneous. The pole pieces of the magnet are so shaped that there is a region in which the product of the field strength and field gradient in the z direction is constant. The sample is placed in this region. The force in this case is independent of the packing of the sample and depends only on the total mass of the material present. The method is sensitive and highly reproducible and can be applied to single crystals. The force is measured as a weight change, using a torsion balance.