Magneto-optic studies of ZnO based magnets

氧化锌是一种不导电的透明晶体。最近，人们发现，如果每50个锌原子中就有一个被锰或钴原子取代，并且这种材料有额外的缺陷，这些缺陷会增加电子使其导电，那么它在室温下就会变得有磁性。磁性来自与磁性原子相关的电子。当然，还有其他常温磁铁，如铁，但它们是金属。磁性半导体是一种非常新鲜和令人兴奋的东西。这种材料在将磁体的存储能力与半导体电子相结合的新设备中有许多应用。磁性是由排列成一块大磁铁的分散的磁性原子产生的。一些电子被困在缺陷周围，一些电子可以自由移动。被困在缺陷附近的电子可能只对其中一个局域磁原子的磁性敏感。电流来自那些可以自由移动的电子，正是这些电子将通过许多磁性原子，并使单个磁性离子上的磁矩排成一条直线。这是因为所有的电子实际上都有自己的小磁矩。谢菲尔德世界领先的实验表明，当掺杂任何一种钒、钛、钴或锰时，氧化锌薄膜的带边跃迁具有磁性特征。这是第一次清楚而明确地证明了氧化锌的传导电子是磁性的，从而证明了氧化锌是一种稀磁半导体。这项提议是利用谢菲尔德的仪器和专业技术，利用磁光光谱、吸收光谱、自由载流子密度的霍尔效应测量和SQUID磁化测量来确定传导电子极化的大小和铁磁性的性质。这具有巨大的影响，因为它表明在室温下观察到的体磁确实与氧化锌有关。它还为开发与磁性相关的存储容量开辟了道路，以便与波长非常小的紫外光相结合，这将允许记录和读取比目前使用红光的标准激光器可能的更高密度的信息。我们在这一领域进行了第一次开创性的实验。现在需要的是建立在我们已经形成的理解的基础上。我们希望将实验技术扩展到包括光的吸收以及光对磁性的响应。我们想用我们开发的方法对不同掺杂浓度、不同厚度和不同温度的掺杂氧化锌薄膜的行为进行详细的研究。我们需要从4月1日开始拨款，这样我们就可以雇用建造我们使用的仪器并测量到目前为止所有测量数据的研究员。如果出现延迟，我们失去了这种连续性，我们将失去我们的世界领先地位……

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...