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>> Typical Physical and Chemical Properties of Some Permanent Magnets

   
Performance Name Unit Sintered NdFeB Bonded NdFeB Sintered Sm2Co17 Sintered SmCo5 Sintered Ferrite Injection Ferrite AlNiCo
Maximum Energy Product ((BH)max) MGOe 28 ~ 52 2 ~ 13 16 ~ 32 14 ~ 24 2 ~ 5 1 ~ 2 1 ~ 13
Intrinsic Coercivity (Hcj) kOe 11 ~ 35 6 ~ 14 8 ~ 35 15 ~ 30 2 ~ 5 2 ~ 4 1 ~ 2
Temperature Coefficient of Br (α) %/°C -0.09 ~ -0.12 -0.10 ~ -0.13 -0.030 ~ -0.045 -0.035 ~ -0.050 -0.2 -0.2 -0.02
Temperature Coefficient of Hcj (β) %/°C -0.40 ~ -0.60 -0.40 ~ -0.60 -0.20 ~ -0.30 -0.20 ~ -0.30 0.3 0.3 0.01 ~ 0.03
Curie Temperature (Tc) °C 310 ~370 300 ~ 350 800 ~ 850 700 ~ 750 450 ~ 480 450 ~ 480 750 ~ 890
Maximum Working Temperature (Tw) °C 230 150 350 250 250 150 500
Recoil Permeability (μrec) - 1.05 1.2 1.05 ~ 1.10 1.05 1.05 ~ 1.20 1.05 ~ 1.20 1.70 ~ 4.70
Density (ρ) g/cm3 7.4 ~7.7 4.0 ~ 6.5 8.3 ~ 8.5 8.1 ~ 8.4 4.8 ~ 5.2 3.3 ~ 3.9 6.9 ~ 7.4
Resistivity (ρ) μΩ·m 1.4 ~ 1.6 - 0.8 ~ 0.9 0.5 ~ 0.6 > 1×108 > 1×108 > 5×103
Thermal Conductivity (λ) W/(m·°C) 8 ~ 10 - 12 13 - - -
Vickers Hardness (Hv) MPa 500 ~ 600 - 500 ~ 600 400 ~ 500 480 ~ 580 - 520 ~ 630
Rockwell Hardness (HRB) MPa - 35 ~ 45 - - - - -
Compressive Strenght (σbc) MPa 1000 ~ 1100 200 800 1000 - - -
Bending Strength (σbb) MPa 200 ~ 400 - 150 180 300 90 ~ 160 -
Tensile Strength (σb) MPa 80 ~ 90 58 35 40 < 100 45 ~ 110 -
Young’s Modulus (E) GPa 150 ~ 200 - 120 130 - - -
Thermal Expansivity (α) 10-6/°C ∥3 ~ 4 1 ~ 2 ∥7 ~ 9 ∥5 ~ 7 7 ~ 15 - -
⊥1 ~ 3 ⊥10 ~ 12 ⊥11 ~ 13
Corrosion resistance ★★☆☆☆ ★★★☆☆ ★★★★☆ ★★★★☆ ★★★★☆ ★★★★☆ ★★★★★
Note:
∗ The above data are only for reference, specific magnets maybe have different values.

>> Glossary of Terms

Magnetic Moment : The magnetic moment is measure of the strength of a magnetic source. Using a fluxmeter and a helmholtz coil, the magnetic moment of a particular permanent magnet can be determined.

Coercive Force, H: The demagnetizing force, measured in Oersteds necessary to reduce the induction, B to zero after a magnet has been previously saturated.

Curie Temperature, T: The temperature at which certain materials lose their permanent magnetic properties, to be replaced by induced magnetism.

Flux, ø : The condition existing in a medium subjected to a magnetizing force. This quantity is characterized by the fact that an electromotive force is induced in a conductor surrounding the flux at any time the flux changes in magnitude. The CGS unit of flux is the MAXWELL.

Gauss, Gs : Lines of magnetic flux per square centimeter, CGS unit of flux density, equivalent to lines per square inch in the English system, and webers per square meter or Tesla in the SI system.

Induction, B : The magnetic flux per unit area of a section normal to the direction of flux. Measured in Gauss, in the CGS system of units.

Intrinsic Coercive Force, Hci : Measured in Oersteds in the CGS system, this is a measure of the material’s inherent ability to resist demagnetization. It is the demagnetization force corresponding to zero intrinsic induction in the magnetic material after saturation. Practical consequences of high Hci values are seen in greater temperature stability for a given class of material, and greater stability in dynamic operating conditions.

Irreversible Loss : Defined as the partial demagnetization of a magnet caused by external fields or other factors. These losses are only recoverable by re-magnetization. Magnets can be stabilized to prevent the variation of performance caused by irreversible losses.

Isotropic Magnet : A magnet material whose magnetic properties are the same in any direction, and which can therefore be magnetized in any direction without loss of magnetic characteristics.

Leakage Flux : That portion of the magnetic flux that is lost through leakage in the magnetic circuit due to saturation or air-gaps, and is therefore unable to be used.

Magnetizing Force, H : The magnetomotive force per unit length at any point in a magnetic circuit. Measured in Oersteds in the CGS system.

Maximum Energy Product, BHmax :The point on the Demagnetization Curve where the product of B and H is a maximum and the required volume of magnet, material required to project a given energy into its surroundings is a minimum. Measured in Mega Gauss Oersteds. MGOe.

Oersted, Oe : A CGS unit of measure used to describe magnetizing force. The English system equivalent is Ampere Turns per Inch, and the SI system’s is Ampere Turns per Meter.

Orientation Direction : The direction in which an anisotropic magnet should be magnetized in order to achieve optimum magnetic properties. Also known as the “axis”, “easy axis”, or “angle of inclination”.

Residual Induction, Br : This is the point at which the hysteresis loop crosses the B axis at zero magnetizing force, and represents the maximum flux output from the given magnet material. By definition, this point occurs at zero air gap, and therefore cannot be seen in practical use of magnet materials.

Saturation : The condition under which all elementary magnetic moments have become oriented in one direction. A ferromagnetic material is saturated when an increase in the applied magnetizing force produces no increase in induction. Saturation flux densities for steels are in the range of 16,000 to 20,000 Gauss.

Stabilization : Exposure of a magnet to demagnetizing influences expected to be encountered in use in order to prevent irreversible losses during actual operation. Demagnetizing influences can be caused by high or low temperatures, or by external magnetic fields.

Pull Force : Pull force measurement are a mechanical method of obtaining a measurement of the holding or pulling strength of a magnet. In this measurement test, a magnet is attached to an actuator with an integrated strain gauge. The opposite side of the magnet is attached to fixed piece of ferromagnetic material such as a plate of mild steed. As the actuator forced the magnet from the steel plate, the force needed to separate the two is recorded by the strain gauge. Pull force tests are not standardized and pull force values provided by manufacturers vary widely and should not be used as the basis of final magnet selection.