The Hysteresis Effect And AC Response Of Single Molecule Magnets

Single molecule magnet is a kind of nano clusters with large spin(S>1/2)and magnetic anisotropy,and shows the macroscopic quantum effects,for example,macroscopic quantum tunneling and macroscopic quantum coherent.Single molecule magnet has become one of good candidate materials for realizing high density information storage and spintronics devices due to good memory and quantum transport properties.Key problem of realizing information processing and quantum computing based on single molecule magnet is how to control molecular magnets spin orientation.Therefore,the quantum transport and quantum manipulation of magnetization in single molecule magnet have attracted wide attention and is a important problem investigated in theory and experiment.In this thesis,magnetic hysteresis and AC response of magnetization of single molecule magnet are investigated based on two external drives.The main research contents and results are as follows:(1)The gate voltage induced hysteresis in single molecule magnet with temperature difference is investigated by using the rate equation.When the gate voltage slowly increases from negative value to positive value and reaches a certain value,and then returns its initial value,the response curve of molecule magnet magnetization to gate voltage is not coincide and forms a hysteresis loop.The hysteresis loop in single molecule magnet is a macroscopic quantum effect and appears only at low temperature and can be explained by dependence of the occupation probability of molecule state on the gate voltage.At the same time,the effects of the temperature,polarization of the ferromagnetic electrode and spin exchange interaction on the area of hysteresis loops is discussed.(2)The response of the magnetization to AC voltage added to two electrodes is investigated in single molecule magnet.The magnetization of the monomolecular magnet changes accordingly when two alternating voltages with opposite phase is applied to two electrodes.Whether the peak value of the alternating magnetization of single molecule magnet can reach saturation magnetization depends on the peak value of alternating voltage.When the peak value of alternating voltage is smaller than a certain critical value,the peak of the alternating magnetization will be smaller than the saturation magnetization.These results can be helpful in designing and developing single molecule magnet information storage element and spintronics devices.