Like ferromagnetism and atomic spectral lines, superconductivity is a quantum mechanical phenomenon. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum mechanical mystery. Only elements with unpaired electrons exhibit paramagnetism, ferromagnetism, and antiferromagnetism. A number of actinide compounds are ferromagnets at room temperature or exhibit ferromagnetism upon cooling. Like ferromagnetism, ferrimagnets retain their magnetization in the absence of a field. This is, like ferromagnetism and ferrimagnetism, a manifestation of ordered magnetism. The Heisenberg model thus cannot explain the observed ferromagnetism in these materials. Heisenberg set Peierls a research project on ferromagnetism. This phenomenon is known as "itinerant ferromagnetism". This model is not the same as the Stoner Model of itinerant ferromagnetism. Q-carbon is reported to exhibit ferromagnetism, fluorescence, and a hardness superior to diamonds. There are 31 magnetic point groups which are compatible with ferromagnetism. One is ferromagnetism in the strict sense, where all the magnetic moments are aligned. This gives rise to ferromagnetism, antiferromagnetism or ferrimagnetism. He also completed experimental studies of ferromagnetism.