Effects of Disorder on Magnetotransport Properties of Sm_{1-x}Sr_{x}MnO_{3} Perovskite Manganites Open Access

[摘要] This thesis focusses on the effects of different kinds of disorder on the physical properties of Sm$_{1-x}$Sr$_{x}$MnO$_{3}$ manganite. We utilized the disorder produced by Ru-doping at the Mn-site and heat treatment to control the physical properties of bulk and thin films of Sm$_{1-x}$Sr$_{x}$% MnO$_{3}$ manganite. For bulk samples, we have studied the effects of Ru doping on structure, magnetic, and magneto-transport properties of polycrystalline Sm$_{1-x}$Sr$_{x}$MnO$_{3}$, $0.45leq xleq $ $0.65$. We have successfully constructed the phase diagram of Ru doped Sm$_{0.55}$Sr$% _{0.45}$MnO$_{3}$ and Sm$_{0.45}$Sr$_{0.55}$MnO$_{3}$ manganites. Furthermore, we have verified that Ru-doping affects the properties of Sm$% _{1-x}$Sr$_{x}$MnO$_{3}$ manganites via tow interactions. (i) Ru increases the Mn$^{3+}/$Mn$^{4+}$ ratio which improves the metallicity due to double exchange interaction enhancement. (ii) High Ru-doping produces ferromagnetic insulating phase due to ferromagnetic superexchange interaction between Mn$% ^{3+}$/Ru$^{4+}$ ions. In addition, we have studied the effect of Ru-doping on the magnetic cluster formation temperature (T$^{ast }$) and paramagnetic/ferromagnetic phase transition temperature (T$_{MIT}$) of Sm$% _{0.55}${Sr}$_{0.45}${Mn}$_{1-x}${Ru}$_{x}${O}$_{3}$ manganite. The T$_{MIT}$ was found to increase with doping but T$^{ast }$ didn;;t significantly change with doping. These results were compared with the theoretical predictions of the effects of magnetic coupling and quenched disorder on the phase diagram of manganites by Burgy et al. (PRL. extbf{87}, 277202 (2001)). On the other hand, we developed a heat treatment technique to relax the strain in as-grown Sm$_{0.55}$Sr$_{0.45}$MnO$_{3}$ films which is responsible for the disappearance of the metal/insulating phase transition (MIT) property in these films. Controlling the strain via heat treatment enabled us to recover the MIT property of Sm$_{0.55}$Sr$_{0.45}$MnO$_{3}$ but with low T$_{MIT}$. We introduced a detailed investigation of the effects of strain, tensile and compressive, on the magneto-transport properties of Sm$_{0.55}$Sr$_{0.45}$MnO$_{3}$ thin films. We found that the anisotropic magneto-resistance (AMR) and temperature coefficient of resistance (TCR) of Sm$_{0.55}$Sr$_{0.45}$MnO$_{3}$ films have large AMR and TCR values compared to other manganites which is important for applications. Doping Sm$_{0.55}$Sr$_{0.45}$MnO$_{3}$ films with $10\%$ of Ru resulted in an increase of the T$_{MIT}$ that enabled us to recover the T$_{MIT}$ of bulk Sm$_{0.55}$Sr$_{0.45}$MnO$_{3}$. A discussion of the effects of Ru-doping on the structure and magneto-transport properties of Sm$_{0.55}$Sr$% _{0.45}$MnO$_{3}$ films is introduced.

[发布机构] University of Alberta

[效力级别] Condensed Matter