Exstrom Labs Magnetism Reference

Magnetic Flux - Φ
Units: weber (MKS), maxwell (CGS)
1 weber = 1 N⋅m/A
1 weber = 10⁸ maxwell

Magnetic Flux Density - B
Units: tesla (MKS), gauss (CGS)
1 tesla = 1 N/(A⋅m) = 1 weber/m²
1 tesla = 10⁴ gauss
1 nanotesla (nT) = 1 gamma = 10^-5 gauss

Magnetic Field Strength - H
Units: A/m (MKS), oersted (CGS)
1 oersted = 10³/(4π) A/m

Relationship Between Magnetic Flux Density and Magnetic Field Strength
B = μH
μ is called the (magnetic) permeability
The permeability of free space is μ₀ = 4π⋅10^-7 T⋅m/A
T⋅m/A = henry/m

1 tesla corresponds to 10⁴ oersted in free space

Magnetization, magnetic susceptibility and permeability
When a material is placed in a magnetic field H, it will respond with its own magnetic field, M, called the magnetization. M is related to H by a dimensionless parameter called the magnetic susceptibility.
M = χH
χ is generally a function of the magnetic field H, and one can define a differential susceptibility as
χ = ∂M / ∂H
The magnetic flux density in the material is B = μ₀(H + M) = μ₀(1 + χ)H = μH
μ = μ₀(1 + χ) is the magnetic permeability of the material.

Permeabilities of materials
copper ⇒ approximately that of free space, μ₀
sheet steel ⇒ depends on H. Average is 4,000 μ₀
cast steel ⇒ depends on H. Average is 1,000 μ₀
See "Circuits, Devices and Systems", Ralph J. Smith, 4th Edition, Ch 20, Fig 20.16, p578

Saturation flux density of materials
Commercial magnetic steels ⇒ 1 to 2 tesla
Ferrite cores ⇒ generally below 0.5 tesla

Gyromagnetic ratio of proton
2.6752218744(11) ⋅ 10⁸ rad/(T⋅s)

Earth's Total Magnetic Field in Longmont, Colorado
as measured with the Magnum (Earth's field NMR) on Jan 3, 2003
53251.31 nT = 0.5325131 gauss