Why do different materials have different permeability and susceptibility values? What are the factors that decide these values? what are the general mechanisms which resist the magnetic field through an object? I have often come across the fact that permeability and susceptibility depend on the nature of the material, but what is it specifically in the "Nature" of the material?
 A: In physics, in particular in electromagnetism, the magnetic permeability of a material is a physical quantity that expresses the ability of the material to become magnetized in the presence of a magnetic field.
Almost all homogeneous materials have a magnetic permeability that can be considered constant, however for some substances (such as iron, cobalt, nickel) it has a behavior that manifests a certain hysteresis, i.e. the permeability shows a dependence on the previous magnetizations and demagnetizations undergone by such materials. The substances for which this behavior occurs are called ferromagnetic.
In non-ferromagnetic substances the magnetic permeability value differs slightly from that of vacuum, and are divided into diamagnetic (in which the relative permeability is less than 1) and paramagnetic (in which the relative permeability is greater than 1). This differs from the electrical permittivity, which can differ greatly from the value in a vacuum and changes significantly depending on the substance, but always assuming higher values ​​than in vacuum.
More specifically, the magnetic field acts on the electrons present on the orbitals of the atoms. In nature there are many elements (see the periodic table of elements) where each has a different atomic number. Without counting exceptions these atoms also have their own number of electrons so the magnetic field acts directly on these electrons. Electrons have the property of possessing a "Spin". Depending on the atom you take (and therefore on the material) you have that the magnetic field is stronger the more electrons there are with the same Spin on the last orbital.
By "nature" of matter we mean its atomic structure. Hope this can help you.
