钙钛矿锰氧化物(La1-xGdx)4/3Sr5/3Mn2O7 (x=0, 0.025) 磁性和输运性质研究

采用传统的高温固相烧结法制备了双层钙钛矿锰氧化物(La_1-xGd_x)_4/3Sr_5/3Mn₂ O₇ (x=0, 0.025)多晶样品. 通过X射线衍射仪研究发现样品为Sr₃Ti₂O₇型四方结构, 空间群为I4/mmm; 磁性测量表明, Gd³⁺掺杂后的样品(La_0.975Gd_0.025)_4/3Sr_5/3Mn₂O₇的三维磁有序转变温度(T_C1^3D)、磁化强度(M)均降低, 这是由于Gd³⁺的掺杂引起晶格的畸变, 从而使得晶格常数发生改变, 减弱了铁磁耦合而导致的; 通过电子自旋共振谱测量发现, 在T_C^3D<T<300 K温度范围内, 两样品在顺磁的基体上均有短程的铁磁团簇存在, 出现了相分离现象. 电性测量表明: 两样品分别在T_C1^3D (La_4/3Sr_5/3Mn₂O₇ 样品的三维磁有序转变温度, T_C0^3D)<T<300 K温度范围内均以三维变程跳跃的方式导电, 分析得出Gd³⁺的掺杂使得载流子局域长度的减小. 这表明载流子需要吸收更多的能量才能克服晶格的束缚进行跳跃, 因此(La_0.975Gd_0.025)_4/3Sr_5/3Mn₂ O₇ 样品的电阻较高.

Magnetic and transport properties of perovskite manganites (La1-xGdx)4/3Sr5/3Mn2O7 (x=0, 0.025) polycrystalline samples

The polycrystalline samples of two-layered perovskite manganites (La_1-xGd_x)_4/3Sr_5/3Mn₂O₇ (x=0, 0.025) are prepared by traditional solid state reaction method. X-ray diffraction measurements show that both samples are of the Sr₃Ti₂O₇ -type tetragonal phase (space groups I4/mmm). Magnetic measurements show that Gd³⁺ doping reduces the magnetic transition temperature (T_C^3D) and magnetization (M) of the doped sample (La_0.975Gd_0.025)_4/3Sr_5/3Mn₂O₇, which is because Gd³⁺ doping induces lattice distortion and change the lattice constant, and subsequently weakens the double exchange interactions. It is found from electron spin resonance measurements that short-range ferromagnetic clusters appear in the paramagnetic background of both samples at temperatures T_C^3D<T<300 K, and therefore phase-separations occur. Electrical transportation measurements show that the electronic conducting mechanism in the temperature range of T_C^3D<T<300 K is in accordance with three-dimensional variable-range hopping. It is found that the sample (La_0.975Gd_0.025)_4/3Sr_5/3Mn₂O₇ has a higher resistance. This is because Gd³⁺ doping reduces the localization length of carriers, and makes conducting carriers absorb more energy to overcome the bound potentials in the lattice.