Understanding Magnetization

Understanding Magnetization

When a material is placed in a magnetic field, there will be some changes in the mass of that material. Since this nature of this entire project is to measure weight and torque of metals in a 1400-degree furnace embedded within a 33 Tesla magnet, it is imperative that the effects of the field on the materials being measure be investigated. Measuring the magnetic properties of the materials being tested is also necessary in the experimental process of this project. The magnetic field also produces a force on the material, which will be calculated as well. This data will establish how sensitive the instrument calibration is to the position and size of the sample material. The calculations provided clearly illustrate how the design of the rod and the holder plate are deduced.

When a magnetic material, is placed within a magnetic field, H, the magnetic material will produce its own magnetization. This phenomenon is called induced magnetization. In practice, the induced magnetic field (that is, the one produced by the magnetic material) will look like it is being created by a series of magnetic dipoles located within the magnetic material and oriented parallel to the direction of the inducing field, H.
A calibration curve must be established to determine the sensitivity of the instrument to the weight and size of the samples. This is highly important for it will drastically effect the measurements being performed. It is also desired to determine the change in mass after it has been exposed to the magnetic field. The force produced on the sample materials by the magnetic field was investigated. All of these findings determined the accuracy of the measurements taken.
Suppose a sample of HgCo(SCN)4, a common material used in the calculations of magnetic forces, is used. The change in mass of a 10mg was calculated to be . That is extremely small value. However, due to the fact that that change is due to a magnetic field and a high temperature furnace, it’s a remarkable finding. It also reemphasizes the sensitivity issue.: The force exerted on the sample materials by the magnetic field was calculated to be for the host material HgCo(SCN)4. Keep in mind that even though the force is small it is being applied to an equally small mass. Again, this effects the design on the rod. The rod must be perfectly asymmetrical so that the materials remain in the center. This is the ideal situation. The rod must be extremely stiff, and the motion of lowering it down into the furnace must be utterly still, so that the materials don’t shift to one side and get pulled by the magnetic field.
The results from the magnetic field calculations were for the flux density and for the magnetization of the solid. These calculations were generated using the following conditions:

is not available for the samples we are using

This is just one of the many calculations that needed to be perform in the design of this high temperature rod. See Calculations for more.

Gouy vs Faraday Techniques

The traditional Gouy technique employs a conventional laboratory balance and large permanent magnets. The magnets remain stationary while the sample is caused to move, giving apparent gain or loss in sample weight. The current required to maintain equilibrium of the balance beam is proportional to the force exerted by the sample.

The second method investigated was the Faraday Method. The Faraday balance is a standard tool for precision studies on weakly magnetic materials. Faraday determined the connection between a changing magnetic field and the associated electric field. In the Faraday Method the primary magnetizing field, H, is usually produced by a horizontal electromagnet. The field gradient is made to be along the vertical direction, so that the magnetic force will add to or subtract from the sample’s weight, and can be detected with a sensitive microbalance. The magnetic force exerted on the samples by the magnetic moment and the field can be calculated by assuming the sample to be used is HgCo(SCN)4.

Glossary of Magnetics

http://gcea.com/glossary.shtm

http://www.magnet.thomasregister.com/olc/magnet/glossary.htm

(Some Common Expressions and Their Meanings)

Ceramic Magnet: Ferrite magnet made from Iron Oxide with additions of barium, strontium or lead.
Coercive Force: BH_C is the demagnetizing force corresponding to zero magnetic induction, B, in a magnetic material after saturation.
Old Units: Oersted
New Units: A/m or kA/m
Curie-Temperature: Is the transition temperature above which a material loses its permanent magnetic properties completely. The Curie temperature is mainly dependent on the chemical composition of the magnetic material.
Demagnetization: Demagnetization results in reduced magnetic properties of a permanent magnet. It occurs when the magnet is exposed to:
Demagnetization Curve: Is the second (or fourth) quadrant of a major hysteresis loop. It indicates the behavior of the induction versus magnetic field. This curve defines the main magnetic properties of a magnet.
Density: Specific weight of material (gr/cm³). Is a ratio to the weight of the water.

Eddy Currents

Circulating electrical currents that are induced in electrically conductive elements when exposed to changing magnetic fields, creating an opposing force to the magnetic flux. Eddy currents can be harnessed to perform useful work (such as damping of movement), or may be unwanted consequences of certain designs which should be accounted for or minimized.

Ferromagnetic Material

A material whose permeability is very much larger than 1 (from 60 to several thousand times 1), and which exhibits hysteresis phenomena.

Flux: Magnetic flux is a contrived but measurable concept that has evolved in an attempt to describe the flow of magnetic field. The flux pattern in a magnetic circuit can be visualized by using iron powder. Mathematically it is the surface integral of the normal component of magnetic induction B, over an area: A^O = SS B . dA
When the magnetic induction is uniformly distributed and is normal to the area, then the flux becomes _OB * A
Conversion: 1 = V_S = 10⁸ Maxwell = 1 Weber
Fluxmeter: Is a galvometer that measures the change of flux linkage with a search coil. Modern instruments are using integrating circuits for measuring flux.
Gauss: Is the old unit of magnetic induction B, in the CGS electromagnetic system. (See "Tesla" for new units.)

1 Maxwell 1 Gauss = ------------- = 1 * 10^-4 Tesla cm₂

It is named after Friedrich Gauss.
Gaussmeter: Instrument for measuring the instantaneous value of magnetic induction, B. The most common principle is the Hall effect. Other principles are nuclear magnetic resonance (NMR) or the rotating coil principle.
Induction: Magnetic induction is the flux per unit area normal to the direction of the magnetic path. (See "Gauss" for conversion units.)
Isotropic: A non orientated material. It has equal physical and magnetic properties in all directions.

Knee of the Demagnetization Curve

The point at which the B-H curve ceases to be linear. All magnet materials, even if their second quadrant curves are straight line at room temperature, develop a knee at some temperature. Alnico 5 exhibits a knee at room temperature. If the operating point of a magnet falls below the knee, small changes in H produce large changes in B, and the magnet will not be able to recover its original flux output without remagnetization.

Leakage Factor: Accounts for the flux leakage from the magnetic circuit. It is the ratio between the magnetic flux at the magnet neutral section and the average flux present in the air gap.
Leakage Flux: Is the flux whose path is outside of the intended magnetic circuit. It is measured in Maxwell.
Magnetic Induction: The flux per unit area normal to the direction of the magnetic path.
Magnetizing: An external field applied to a magnet to charge it or magnetize it. For ferrites, the field strength should be approximately three times the value of its coercive force. For magnetizing, DC or pulse fields can be applied with pulse ties less than l millisecond, if no iron is present in the magnetizing path.

Magnetic Flux

The total magnetic induction over a given area. When the magnetic induction, B, is uniformly distributed over an area A, Magnetic Flux = BA.

Magnetizing Force, H

The magnetomotive force per unit length at any point in a magnetic circuit. Measured in oersteds in the cgs system

Oersted: Is the old unit for the magnetic field strength, H, in the CGS electromagnetic system. One oersted equals to a magneto motive force of one Gilbert per centimeter of flux path.
Conversion: 1 0e = 0.796 A/cm
Operating Temperature: A magnet is not allowed to be exposed to a temperature exceeding the operating temperature without permanent magnetic losses.
Orientation Direction: A permanent magnet has its highest magnetic properties in direction of orientation. For ring and disc shape magnets, the typical direction of orientation is axial. For rectangular and cubical shapes, the orientation is through the height (h). Arc and segment magnets are orientated through the radius or through the diameter. Orientation of a magnet is achieved by applying a magnetic field to a powder before and during compaction.
Oxide Magnet: Equal to a ferrite magnet; made from oxides and carbonates of iron, barium or strontium.

Paramagnetic Material:

A material having a permeability slightly greater than 1.
Permanent Magnet: A body capable of maintaining a magnetic field at other than cryogenic temperature with no expenditure of power.
Permeability: Is the general term used to express the relationships between magnetic induction, B and the field strength, H.
Ratio of Dimension h:d: Also named L ratio d. It is the ratio of the length of a magnet to its diameter, or to the diameter of a circle of equivalent cross sectional area.

Relative Permeability

The ratio of permeability of a medium to that of a vacuum. In the cgs system, the permeability is equal to 1 in a vacuum by definition. The permeability of air is also for all practical purposes equal to 1 in the cgs system.

Residual Induction: Br is the magnetic induction corresponding to zero magnetizing and force in a magnetic material after saturation in a closed circuit.
Reversible Losses: Reversible losses are changes of magnetic properties depending on the temperature. These losses are fully recovered by returning to the original temperature.
Strontium: Chemical element used as a component for ferrite magnet production.
Tesla: Induction, flux per unit area
Conversion: 1 Tesla = 1 Vs/m² or 10,000 Gs
The unit Tesla is named after Nicola Tesla.
Weber: New unit for magnetic flux. (See "flux."")
Conversion: 1 Weber = 10^-8 Maxwell = 1 Vs
The unit Weber is named after Professor Wilhiem Weber.

	high A-C field
	reverse fields applied by electromagnets or other permanent magnets
	exposure at elevated temperatures