That's a broad question ... What level are you pegging (e.g. undergraduate, Master's, Ph.D.?), and, if at post-graduate level, there are so very many areas of specialization, that the list of "top books" easily swells into the thousands of titles .....
It is not only the problem for what audience the book is written. There are "big" books, like "Magnetism and Magnetic Materials" by J.M.D. Coey (more than 600 pages!), which will tell you "everything" about magnetic phenomena. Yet, if you are interested in a specific "small" problem, you better switch to something less known but better concentrated on this very subject.