【摘要】 基于Winful的隧穿时间模型,对普通金属/铁磁绝缘体/普通金属(NM/FI/NM)、普通金属/铁磁半导体/普通金属(NM/FS/NM) 2种隧道结中的隧穿时间(居留时间和相位时间)和自旋极化率进行了研究.NM/FI/NM结中隧穿电子的自旋极化源于FI层的自旋过滤效应.而NM/FS/NM结中隧穿电子的自旋极化则源于FS层中磁性和Rashba自旋轨道耦合效应的共同作用.计算结果表明:在NM/FI/NM隧道结中,随着铁磁绝缘体层势垒厚度的增加,自旋极化率变化逐渐增加到趋于饱和并始终保持为正值.与之相应的自旋上下电子的居留时间和相位时间也随着增加,但自旋向下电子的隧穿时间总是大于自旋向上电子.铁磁绝缘体层中分子场的增加会导致自旋极化率逐渐增大并始终为正,相应的自旋向下电子的居留时间和相位时间总是大于自旋向上电子,但自旋向上电子的时间逐渐增加而自旋向下电子则相应减少.铁磁绝缘层势垒高度的变化会导致自旋极化率从负到正的转变.当自旋极化率为负时,相应的自旋向上电子的隧穿时间大于自旋向下电子的隧穿时间.在NM/FS/NM结中,由于Rashba自旋轨道耦合作用,自旋向上电子和自旋向下电子的隧穿时间随铁磁半导体层的厚度、分子场和Rashba耦合系数的变化呈现出周期性振荡变化的趋势.与之相应的自旋极化率从正到负,也呈周期性的振荡变化.但当自旋向下电子的隧穿时间大于自旋向上电子的时候,极化率为负,反之为正;这个结果和NM/FI/NM隧道结中的情况刚好相反.更多还原

【Abstract】 Based on the Winful’s tunneling time model,the tunneling time( dwell time and phase time) and spin polarization in normal metal/ferromagnetic insulator/normal metal( NM/FI/NM) and normal metal/ferromagnetic semiconductor/normal metal( NM/FS/NM) junctions are discussed. The spin polarization of the tunneling electrons in the NM/FI/NM junction is due to the spin filtering effect of the FI layer. The spin polarization of tunneling electrons in the NM/FS/NM junction is due to the combined effect of magnetic and Rashba spin-orbit coupling in the FS layer. The numerical results show that,in NM/FI/NM junctions,when the barrier thickness of the ferromagnetic insulator layer is increased,the spin polarization gradually increases to saturation and remains positive at all times.Accordingly,the dwell time and phase time of the spin-up and down electrons are also increasing and the tunneling times of the spin down electrons are always greater than those of the spin up electrons. When the molecular field in ferromagnetic insulator layer is increased,the spin polarization increases gradually and is always positive. The corresponding dwell times and phase times of the spin down electrons are always greater than those of spin up electrons,but the tunneling times for spin up electrons increase and for spin down electrons decrease. The change of barrier height of the ferromagnetic insulating layer can lead to spin polarization from negative to positive. When the spin polarization is negative,the tunneling times of the corresponding spin electrons are greater than the tunneling times of the spin down electrons. In NM/FS/NM junctions,as the Rashba spin orbit interaction,the tunneling times for the spin up and spin down electrons show periodic oscillations with thicknesses,molecular fields and Rashba coupling coefficients in ferromagnetic semiconductor layer. Accordingly,the spin polarizations also oscillate periodically and can change from positive value to negative value. But when the tunneling times of the spin down electrons are greater than those of spin up electrons,the spin polarizations are negative and vice versa. These results are just contrary to the situations in NM/FI/NM junctions.更多还原