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Neodymium Magnet Basic Knowledge 2015-10-16

Inreversible Temperature Coeffficients: Take 20°C and 120°C as example,

α(Br)=(12.07-13.39)÷13.39/(120°C-20°C)x100%

Remanence=Br

Coercive Force= Hcb

Instrinsic Coercive Force=Hcj

Maximum Specific Energy Product=BH(max)

Curie Temperature:

The Curie-Weiss Law is an adapted version of Curie's Law.

The Curie-Weiss Law is a simple model derived from a mean-field approximation, this means it works well for the materials temperature,T, much greater than their corresponding Curie Temperature,T_c, i.e. T >> T_c; however fails to describe the magnetic susceptibility, χ, in the immediate vicinity of the Curie point because of local fluctuations between atoms.

Both Curie's Law and the Curie-Weiss Law do not hold for T < T_c.

Curie's Law for a paramagnetic material;

Definition
χ	the magnetic susceptibility; the influence of an applied magnetic field on a material
M	the magnetic moments per unit volume
H	the macroscopic magnetic field
B	the magnetic field
C	the material-specific Curie constant


µ₀	the permeability of free space. Note - in CGS units is taken to equal one.^[24]
g	the Landé g-factor
J(J+1)	the eigenvalue for eigenstate J² for the stationary states within the incomplete atoms shells (electrons unpaired)
µ_B	the Bohr Magneton
k_B	Boltzmann's constant
total magnetism	is N number of magnetic moments per unit volume

The Curie-Weiss Law is then derived from Curie's Law to be

where

λ is the Weiss molecular field constant.

Curie Temperature of materials
Material	Curie Temperature (K)
Iron (Fe)	1043
Cobalt (Co)	1400
Nickel (Ni)	631
Gadolinium (Gd)	292
Dysprosium (Dy)	88
MnBi	630
MnSb	587
CrO₂	386
MnAs	318
EuO	69
Iron(III) oxide (Fe₂O₃)	948
Iron(II,III) oxide (FeOFe₂O₃)	858
NiOFe₂O₃	858
CuOFe₂O₃	728
MgOFe₂O₃	713
MnOFe₂O₃	573
Y₃Fe₅O₁₂	560

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