why are some materials magnetic and not others?
The material must be capable of interacting with the magnetic field. Apparently all materials have some interaction with magnetic fields, but most are effected so little that they are called non-magnetic. Wood, glass, some ceramics, rubber and plastics are all good examples. Items which do interact are called magnetic and are almost always composed of a ferromagnetic material like iron, cobalt, nickle and ceramics which contain iron oxide. At a low temperature, the metals gadolinium and dysprosium are also magnetic.
This may be surprising to some, but all matter is magnetic. It's just that some materials are much more magnetic than others. The main distinction is that in some materials there is no collective interaction of atomic magnetic moments, whereas in other materials there is a very strong interaction between atomic moments. The magnetic behavior of materials can be classified into the following five major groups: 1. Diamagnetism 2. Paramagnetism 3. Ferromagnetism 4. Ferrimagnetism 5. Antiferromagnetism Magnetic Properties of some common minerals Materials in the first two groups are those that exhibit no collective magnetic interactions and are not magnetically ordered. Materials in the last three groups exhibit long-range magnetic order below a certain critical temperature. Ferromagnetic and ferrimagnetic materials are usually what we consider as being magnetic (ie., behaving like iron). The remaining three are so weakly magnetic that they are usually thought of as nonmagnetic. cc
