Remarks M= XmH is an assumption that m is proportional to h and in the same direction A magnetic material satisfying this relation is called isotropic and linear Ferromagnetic materials do not satisfy this relation A paramagnetic material has Xm l by several orders, and xm∝x1/ a diamagnetic material has Xm <0, i.e. M is in the opposite direction to the external field, ur <1 and ulm is independent of the temperature T