Study On Spin Transport Properties Of Metal Porphyrins-based Molecular Devices

Molecular devices have grown rapidly in recent decades.Many molecular devices with special features have been discovered by scientists through theoretical and experimental methods,and are the substitutes for future electronic components.Regarding the design of molecular devices,the current research focuses on the selection of core molecules,the connection bettween molecules and electrodes,and the influence of internal and external factors on the device.The critical points are the selection of core molecules and the connection bettween molecules and electrodes.In this paper,the spin transport properties of metal porphyrin molecular devices were investigated by first-principles.It is proposed to improve the spin transport performance of molecular devices by changing the central metal ions of metal porphyrins and the spin states of porphyrin molecules.The main research contents are as follows:(1)By calculating the spin transport properties of metal(Mn,Fe,Co,Cu)porphyrin dimer molecule devices,it is found that all molecule devices exhibit excellent spin filtration behavior when electrodes are in the ferromagnetic state,and the spin filtration efficiency are close to 100%.Each device exhibit a giant magnetoresistance effect with magnetoresistance rate reach 107%,which increases with increasing bias voltage.Above result plays an important role in the design of future dual-function molecular devices.(2)Heme/graphene heterojunction was constructed.The spin transport calculations of the heterojunction show spin-filtering effects when electrodes are in a ferromagnetic state,and the spin filter coefficients are dependent on the spin setting of the heme molecule.In addition,the transition between the high spin state and the low spin state of the heme causes the spin current of the heterojunction to reverse,and the low spin heterojunction exhibits spin rectification with the rectification ratio of 7.3.The results suggest that the spin state of the molecule has an effect on the spin transport behavior of the device,which has a guiding role for molecular device in the future research.The metal porphyrins formed molecular device with the graphene nanoribbon electrodes by covalent bonds and van der Waals force,respectively.The spin transport properties show that the transmission paths of spin electrons are different in the two kinds of connection modes.The transport channels of the spin electrons in the covalently attached molecular devices are mainly the 7r-conjugate in metal porphyrins,while the transfer of spin electrons were mostly achieved via the metal ions when electrodes interact with the molecule through van der Waals forces.The results indicate that the interaction between the molecule and electrodes will affect the spin transport properties,which provides some references for the design of the molecular device.