Magnetization, bound current and magnetic field strength
Magnetization M contributes bound volume current J_b=∇×M and surface current K_b=M×n.
Key knowledge
Magnetization M contributes bound volume current J_b=∇×M and surface current K_b=M×n. H=B/μ₀−M separates macroscopic magnetization from free currents, giving ∇×H=J_free+∂D/∂t. A local linear isotropic medium can use M=χ_mH and B=μH.
Values and equations
J_b=∇×M; K_b=M×n; B=μ₀(H+M); ∇×H=J_free+∂D/∂t
- M,H
- Magnetization and magnetic field strength A m⁻¹
- J_b,J_free
- Current densities A m⁻²
- K_b
- Surface current density A m⁻¹
- B
- Magnetic flux density T
- μ₀,μ
- Permeabilities H m⁻¹
- D
- Displacement C m⁻²
- t
- Time s
- n,χ_m
- Unit normal and susceptibility
Conditions and scope
- Macroscopic fields; for the displayed K_b=M×n formula n points outward from the magnetized body and exterior M is zero. Between two magnetized media use (M₁−M₂)×n with n from 1 to 2. J_b here is the magnetization contribution; polarization current ∂P/∂t enters the D time derivative.
- The scalar χ_m relation is a constitutive model, not a general definition of magnetism. Ferromagnetic hysteresis, anisotropy and nonlinear or dispersive response need further state and history information.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Richard Fitzpatrick / University of Texas at Austin2 sources
Evidence and review
Classical Electromagnetism (2014): Magnetization: Equations 680–689: magnetization curl, separate polarization current, H and macroscopic Ampère–Maxwell law. Surface current is derived by integrating the curl across a piecewise M discontinuity; it is not a displayed equation on this page. Classical Electromagnetism (2014): Magnetic susceptibility and permeability: Equations 690–692: explicitly assumed approximately linear isotropic M=χ_mH, B=μH and μ=μ₀(1+χ_m). No susceptibility table values or claim that every weak magnetic response is negligible is used.
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