Independent-spin paramagnetism and Curie law
For independent spin-½ moments of magnitude μ in magnetic flux density B, a moment has energies ±μB, partition sum 2cosh(μB/(k_BT)) and mean moment μtanh(μB/(k_BT)).
Key knowledge
For independent spin-½ moments of magnitude μ in magnetic flux density B, a moment has energies ±μB, partition sum 2cosh(μB/(k_BT)) and mean moment μtanh(μB/(k_BT)). For dilute moments with B≈μ₀H and weak field, χ≈nμ₀μ²/(k_BT).
Values and equations
⟨μ_z⟩=μtanh(μB/(k_BT)); χ≈nμ₀μ²/(k_BT)
- μ,⟨μ_z⟩
- Moment magnitude and mean projection J T⁻¹
- B
- Magnetic flux density T
- n
- Moment number density m⁻³
- μ₀
- Vacuum permeability H m⁻¹
- k_B
- Boltzmann constant J K⁻¹
- T
- Temperature K
- χ
- Dimensionless differential susceptibility
Conditions and scope
- Noninteracting identical two-state moments in thermal equilibrium, T>0, ignoring orbital diamagnetism and internal-field interactions.
- Curie behavior differs from the nearly temperature-independent Pauli response of degenerate itinerant electrons; the formula does not describe ordered phases.
Sources · 1
References
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Evidence and review
Solid State Physics: third-year lecture notes (2012): Section 18.4, equations 18.6–18.9: free spin-½ partition function, moment and weak-field susceptibility; μ generalizes the displayed μ_B moment magnitude.
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Entry details
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