Page "Mu-metal" Paragraph 2

Mu-metal typically has relative permeability values of 80, 000 – 100, 000 compared to several thousand for ordinary steel.

It is a " soft " magnetic material ; it has low magnetic anisotropy and magnetostriction, giving it a low coercivity so that it saturates at low magnetic fields.

This gives it low hysteresis losses when used in AC magnetic circuits.

Other high permeability nickel-iron alloys such as permalloy have similar magnetic properties ; mu-metal's advantage is that it is more ductile and workable, allowing it to be easily formed into the thin sheets needed for magnetic shields.