Ultrafast Spin Dynamics On Carbon Nanotubes With Adsorbed Transition Metal Atoms

With the continuous development of the information technology,the size of electronic logic devices has been reduced and gradually approached the physical limit.With the deepening of the research on various aspects of electric devices,people began to seek for spintronic devices which can break through the size limit and be used for high-density magnetic storage.Carbon nanotubes(CNT)exhibit unique physical and chemical features,and show excellent mechanical and electrical properties.Being adsorbed by transition metal atoms,they have potential applications in nano devices and spintronics due to the extraordinary electronic and magnetic properties and thus have attracted researchers'interestes.In this thesis,by using the first principles method,we study properties of transition metal atoms adsorbed carbon nanotubes structure TM1,2@CNT(4,4)and TM1,2?CNT(4,4),such as the geometric configurations,infrared spectra,magnetic anisotropies(here TM=Fe,Co,Ni,@indicates the structure inside the carbon nanotubes and?indicates the structure outside the carbon nanotubes),and predict the A process based laser-induced spin dynamics.The main contents and results are as follows:Firstly,the optimization procedures of structures TM1,2@CNT(4,4)and TM1,2?CNT(4,4)are performed with the Hartree-Fock(HF)method.For each structure,various adsorption positions,both inside and outside of the CNT,were tried,and the stable configuration of each structure was determined through the comparsion of the energy and absence of the virtual frequencies of the infrared spectrum.Meanwhile,the normal modes of each structure as well as the corresponding frequency ranges were analysized,which show decent agreement with other work.Secondly,the ground states and excited states of each structure are obtained by using the symmetric adaptive cluster configuration interaction method(Symmetry-adapted cluster configuration interaction,SAC-CI).It is found that for the structures with the same kind of magnetic species,as the magnetic atoms changes from adatom to dimer,the band width becomes narrower and the number of low-energy states below 3 eV increases.In addition,through the study of the magnetization curve of the ground state of each structure,it is found that the spin expectation of each structure increases with the increase of the magnetic field intensity,except for structure Ni@CNT(4,4),until it reaches the saturation threshold.Specifically,the response of different structures to the magnetic field intensity is different.The spin expectation of values of Fe1,2?CNT(4,4)and Co2?CNT(4,4)(The magnetic field strength is between 10-6 and 10-5 at.un.)change greatly with the increase of magnetic field strength,while the spin expectation values of structure Fe1,2@CNT(4,4)and Co2@CNT(4,4)change little;the spin expectation of values of Co/Ni2@CNT(4,4)and Co2@CNT(4,4)(The magnetic field strength is between 10-5 and 10-2 at.un.)change greatly with the increase of magnetic field strength,while the spin expectation values of structure Co/Ni2?CNT(4,4)and Co2?CNT(4,4)change little;the structure Ni@CNT(4,4)is always at the saturation threshold when the magnetic field intensity is between 10-6 and 10-2 at.un.At the same time,the spin localization of the first two kinds of magnetic atoms is more obvious than that of Ni1,2@CNT(4,4)and Ni1,2?CNT(4,4),and the states with good spin localization are more thus richer spin dynamics processes can be realized.Finally,the ultrafast spin dynamics induced by laser pulses is studied.The results show that Fe/Co@CNT(4,4)and Fe/Co?CNT(4,4)are easier to achieve ultrafast spin flip dynamics,while for Ni adsorbed CNT spin flip is only realized on Ni?CNT(4,4)with fidelity above 96%;Spin flip is both achievable in Fe/Co2@CNT(4,4)and Fe/Co2?CNT(4,4),with fidelity high than 84%;In addition,we find that spin-transfer and charge transfer are also realized on Fe2?CNT(4,4)with fidelity of 87.9%and 97.9%,respectively.However,none of the above spin dynamics has been found in Ni2CNT@(4,4)and Ni2CNT?(4,4)due to there are few spin-localized states and no spin localization on two magnetic atoms respectively.In this thesis,the ultrafast spin dynamics of TM1,2@CNT(4,4)and TM1,2?CNT(4,4),(TM=Fe,Co,Ni)structures are systematically studied by using the first principles method based on the ? process.The results provide valuable reference for the design and application of related spintronic devices.