Jahn-Teller distortion and magnetoresistance in electron doped Sr

Neutron and electron diffraction, electrical transport and magnetic measurements have been carried out on a newly synthesized electron doped Sr1-xCexMnO3 (x = 0.1, 0.2, 0.3 and 0.4) system. For x=0.1, while cooling, it undergoes a first-order metal-insulator transition at 315 K which is associated with a structural transition from cubic (Pm3m) to tetragonal (I4/mcm) due to Jahn-Teller ordering ($T_{\mathrm{JT}} \sim 315 \mathrm{K}$) which stabilizes a chain like (C-type) antiferromagnetic ground state with $T_{\mathrm{N}} \sim 290 \mathrm{K}$. The antiferromagnetic insulator state is insensitive to an applied magnetic field of 7 T. With increase of x, while the nuclear structure at room temperature for x=0.2 and 0.3 remains tetragonal, for x=0.4 it becomes orthorhombic (Imma) where the doping electrons seem to occupy mainly the $d_{x^2-y^2}$ symmetry. Further, the JT distortion and the antiferromagnetic interactions decrease with doping and a small negative magnetoresistance appears for $x \geq 0.2$. Magnetic measurements show that the dilution of antiferromagnetic interaction results into a spin glass like behaviour at low temperature for the samples with x=0.3 and 0.4. This behaviour is in contrast with the CMR properties of calcium based electron doped systems and hole doped manganites. The stability of C-type antiferromagnetic ordering in the electron doped system with large A-site cationic size may be responsible for the absence of double exchange ferromagnetism and CMR effect