Spontaneous Spin Polarization Properties Of Organic Molecules Adsorbed On Metal Surfaces: First Principles Calculations

In the past few decades,a significant progress in the study of organic semiconductors is their applications in spintronics.Organic semiconductors have weak spin orbit coupling and weak hyperfine interactions,which are contributed to the spin polarized injection and transportation.Due to the size diversity and the variety of organic molecules,it is possible to produce high quality and low cost information equipments.Based on organic molecular devices,the study of its spin injection,spin polarized transportation,spin storage and spin detection have become hot topics in today's research field of spintronics.There are two basic types of device structures in organic spintronics.One of them is organic magnetic device,in which people mainly focus on the spin-polarized electron(hole)injection,transportation and detection in organic materials when they contacted with ferromagnetic materials.Another kind of device structure is organic non-magnetic devices,which doesn't contain any magnetic element.People mainly study the change of the structure properties under external fields,including the change of magnetoresistance,electroluminescence,photocurrent,photoluminescence,et al,which are called organic magnetic field effects.The current research are focused on the ferromagnetic/organic interface properties,however,the properties of non-magnetic device under the various external conditions,also have attracted considerable attention.In this paper,by using the first principles method based on density functional theory,spontaneous spin polarization properties of organic molecules adsorbed on the metal surfaces are studied.Effects of different electrodes and organic materials,different adsorption configurations and different external conditions of the above two kinds of device interfaces are calculated.The main research content is as follows:(1)Spin polarization properties of benzene molecule which is adsorbed at Fe(100)surface are discussed.After adsorbed at Fe(100)surface,the benzene molecule is no longer spin degeneracy,an obvious spin polarization appeared.It is also found that the interfacial spin polarization for the horizontal adsorption is bigger than that of the vertical adsorption.The biggest spin polarization will be obtained when the center of the benzene ring is directly placed above the Fe atom.(2)Spin pin polarization properties of thiophene molecule adsorbed on the Fe(100)surface.The thiophene molecule is spin nondegenerate after adsorption.It is also found that the interfacial spin polarization is different under different contact configurations,the biggest one will be obtained when the sulphur atom of the thiophene is directly placed above the Fe atom at the horizontal direction.Equally,for the horizontal adsorption and the vertical adsorption,interfacial spin polarization inversion is obtained by adjusting the adsorbed position.(3)Spin polarization properties of thiophene molecular adsorbed on Co,Fe,and Ni surface.Different electrodes induce different spin polarization,and in which the Fe electrode will bring the biggest spin polarization of the thiophene molecule.(4)Spontaneous spin polarization of benzene molecular adsorb on nonmagnetic Cu(100)under external electric field.Two contact configurations are calculated.Our simulations show that an obvious spontaneous spin polarization phenomenon generated in the benzene molecule by increasing the external electric field.The strength of orbital coupling is related with the electric field intensity,so the change of the electric field induce spin polarization oscillation,and the maximum spin polarization are obtained near the electric field of 2.0e V/?.