Pauli spin susceptibility of a free Fermi gas
At weak magnetic field and T≈0, a noninteracting spin-½ electron gas has spin magnetization M=μ_B²g(E_F)B and susceptibility χ_P=μ₀μ_B²g(E_F).
Key knowledge
At weak magnetic field and T≈0, a noninteracting spin-½ electron gas has spin magnetization M=μ_B²g(E_F)B and susceptibility χ_P=μ₀μ_B²g(E_F). Here g is the zero-field density of states per volume including both spins; for a three-dimensional quadratic dispersion, g(E_F)=3n/(2E_F).
Values and equations
M=μ_B²g(E_F)B; χ_P=μ₀μ_B²g(E_F); g(E_F)=3n/(2E_F)
- M
- Spin magnetization A m⁻¹
- B
- Internal induction T
- χ_P
- Dimensionless spin susceptibility
- μ_B
- Bohr magneton J T⁻¹
- μ₀
- Vacuum permeability N A⁻²
- g(E_F)
- Two-spin density of states per energy and volume J⁻¹ m⁻³
- E_F
- Fermi energy J
- n
- Electron number density m⁻³
Conditions and scope
- μ_BB≪E_F, k_BT≪E_F, no spontaneous order and negligible interaction enhancement; χ_P describes the spin contribution alone.
- Use B≈μ₀H at leading small susceptibility. Orbital diamagnetism, exchange effects and nonparabolic bands are additional effects; the chemical potential is unchanged only to first order in this weak-field expansion.
Sources · 1
References
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Evidence and review
Solid State Physics: third-year lecture notes (2012): §4.2 equations 4.10–4.11: density of states includes both spins; §4.3 equations 4.12 and the displayed magnetization/susceptibility result, with weak-field state-counting interpretation.
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