Magneto-optic studies of ZnO based magnets

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Zinc oxide is a transparent crystal that does not conduct electricity. It is not magnetic.Recently it has been found that if one in 50 of the Zn atoms is replaced by a manganese or cobalt atom and the material has additional defects that add electrons that cause it to conduct electricity then it becomes magnetic at room temperature. Magnetism comes from the electrons that are associated with the magnetic atoms.Of course there are other room temperature magnets such as iron but they are metals. A magnetic semiconductor is something really new and exciting. Such a material has many applications in new devices that combine the memory capabilities of a magnet with semiconductor electronics. The magnetism arises from the widely separated magnetic atoms that line up to make one big magnet. Some of the electrons are stuck around the defects and some are free to move. An electron that is stuck near a defect may only be sensitive to the magnetism of one of the localised magnetic atoms. The electric current comes from those that are free to move and it is these electrons that will move past many magnetic atoms and cause the magnetic moments on the individual magnetic ions to line up. This happens because all electrons actually have their own little magnetic moment.Sheffield WORLD LEADING experiments show that the band edge transitions of ZnO films have a magnetic signature when doped with any one of vanadium, titanium, cobalt or manganese. This is the first clear and unambiguous demonstration that the conduction electrons of ZnO are magnetic and hence that that ZnO is a dilute magnetic semiconductor. This proposal is to use the apparatus and expertise in Sheffield to use magneto-optic spectra, absorption spectra, Hall effect measurement of the free carrier density and SQUID magnetisation measurements to establish the magnitude of the conduction electron polarisation and the nature of the ferromagnetism.This has enormous implications because it shows that the bulk magnetism observed at room temperature is really connected with the ZnO. It also opens the way for the exploitation of the storage capacity associated with the magnetism to be integrated with ultra violet light, that has a very small wavelength, this will allow a much higher density of information to be recorded and read than is currently possible with the standard lasers that use red light. We have made the first groundbreaking experiments in this area. What is needed now is to build on the understanding that we have developed. We want to extend the experimental technique to include the absorption of light as well as the response of the light to the magnetism. We want to use the method that we have developed to make the detailed studies of the behaviour of the doped ZnO films with different concentrations of dopants, different thicknesses and different temperatures. We need the grant to start on 1 April so that we can employ the research fellow who has built the apparatus that we use and also taken all the measurements so far. If there is a delay and we lose this continuity we shall lose our world leading position...