I think I should chime in my 2-cent here.
You need to be a bit more careful in defining "Material Science" as an academic major. In many schools, "Material Science" is a part of the engineering college. So while there may be a large overlap in the content of study with those studying the physics of materials, such area of study focuses more on the application, fabrication, and engineering aspect of material science.
However, if the study of "Material Science" is within the physics department, then this is more likely to be known as "Condensed Matter Physics". Again, this may involve application and fabrication of materials, but also involve in a large part the study of the physics of materials, especially many-body physics of the strongly correlated systems. This field of physics includes magnetism, low-dimensional systems, semiconductors, superconductors, magnetoresistance, etc.
In many instances, this boundary is not that significant at the very end. For example, the American Physical Society lumps both condensed matter physicists and material scientists into one division under its wing called the the Division of Condensed Matter Physics/Material Sciences (no brainer there!). Together, the make up the largest division of the APS.
What it boils down to is the subtle area of interest that YOU have, or might want to go into. The best thing to do is go to the various schools that you might want to apply to, look at all the reseach areas that are available, how active are the faculty members in those areas, look at the various publications they produce, and select one or two that you might like to work in. While you may have to indicate the area you want to go into in your graduate school application, you really don't have to make a firm commitment to any area until you pass your qualifier. Most faculty members don't want you to work for them anyway till you do! :)
Zz.
