Which term refers to a material that has a permeability less than that of a vacuum?

The term that describes a material with permeability less than that of a vacuum is diamagnetic. In magnetic terms, permeability is a measure of how easily a material can support the formation of a magnetic field within itself. A diamagnetic material has a permeability that is less than that of a vacuum, which means it does not support the magnetic field as strongly as a vacuum does; instead, it weakly repels magnetic fields.

Diamagnetic materials have no unpaired electrons and, when exposed to a magnetic field, create a very weak, negative magnetization. This results in a slight repulsion from the magnetic field. Common examples of diamagnetic materials include bismuth, copper, and graphite.

Comparatively, ferromagnetic materials have a permeability greater than that of a vacuum and can maintain a magnetic field even after the external field is removed, thanks to their unpaired electrons which allow strong magnetic alignment. Paramagnetic materials also have a permeability greater than that of a vacuum but only exhibit magnetic properties in the presence of an external magnetic field, and like ferromagnetic materials, they have unpaired electrons. The general term "magnetic" can refer to both ferromagnetic and paramagnetic materials, which do not fit the description of having a permeability lower