magnetic permeability

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The ability of a substance to acquire high magnetization in relatively weak magnetic fields.

Wiktionary

1. n. physics a measure of the magnetisation of a material in a magnetic field; symbol μ. Materials with values less than 1 are diamagnetic those above are paramagnetic.

GNU Webster's 1913

1. n. (Physics) the specific capacity of a body for magnetic induction, or its conducting power for lines of magnetic force.