作　　者： ; ; ; ;

机构地区： 中国科学院物理研究所

出　　处： 《物理学报》 2004年第11期3909-3915,共7页

摘　　要： 在厚度为 2 5— 4 0 0nm范围内 ,系统地研究了 (0 0 1)SrTiO3(STO) ,(0 0 1)LaAlO3(LAO)衬底上La0 6 7Ca0 33MnO3(LCMO)薄膜的电输运与居里温度TC 随薄膜厚度及衬底的变化 .结果表明 ,随薄膜变薄 ,电阻率 ρ增加 ,TC降低 .对于同一薄膜厚度 ,LCMO STO薄膜的 ρ大于LCMO LAO基上的薄膜的 ρ .TC与衬底的依赖关系则与 ρ相反 .分析表明 ,LCMO薄膜的低温区电阻温度 (ρ T)符合关系式 ρ =ρ0 +Bωs sinh2 (ωs 2 kBT) +CTn,其中 ρ0 为剩余电阻 ;等号右端第二项反映软光学模声子对电子散射的贡献 ;第三项包括其余可能散射机理在电输运过程中所起的作用 ;B ,ωs(软光学模声子的平均频率 )与C都为拟合系数 .高温区的电输运则由小极化子跃迁模型 ρ =DT×exp(Ea kBT)描述 (Ea为极化子激发能 ) .根据 ρ0 ,ωs,Ea以及TC变化 ,初步讨论了薄膜中的厚度与应变效应 .进一步研究发现ωs,Ea的变化与TC 相关 ,从而说明极化子效应为影响TC La 0.67Ca 0.33MnO 3 films with thickness between 25 and 400nm were fabricated on (001)SrTiO 3 and (001)LaAlO 3 substrates, using pulsed laser deposition. The magnetization and resistivity ρ of the films were studied as functions of thickness. The reduction of t causes the decrease of the Curie temperature T C in addition to the increase of ρ of the films. Compared with the compressive strain in the La 0.67Ca 0.33MnO 3/LaAlO 3 films, the tensile strain in the La 0.67Ca 0.33MnO 3/SrTiO 3 films causes a faster reduction of T C with t, and a larger value of ρ 0. The low_temperature ρ is found to follow well ρ=ρ 0+Bω s/sinh 2(ω s/2k BT)+CT n, with ρ 0 being the residual resistivity. The second term arises from the scattering by a soft optical phonon mode, and the third term denotes the other possible transport mechanisms. B, ω s(the frequency of a soft optical mode) and C are fitting parameters. At temperatures higher than T C, ρ of all the films show activated conduction with ρ=DTexp(E a/k BT). Here, E a is the activation energy. Based on the investigation of ρ 0, ω s and E a, the thickness and strain effects in the films are discussed, separately. Further study shows that the variation of T C is mainly associated with E a and ω s, confirming the crucial role of the electron_phonon coupling in the strain effects on T C.

关 键 词： 声子 薄膜厚度 应变效应 极化子效应 激发能 电子散射 衬底 输运

领　　域： [理学] [理学] [理学] [理学]