Magnetic and Electronic Transitions in a Highly-Doped Mott Insulator

Sr3Ir2O7’s insulating nature has been attributed to the combined effects of crystal field splitting, spin-orbit coupling, and a Coulomb interaction. This combination makes it an interesting subject of study, particularly since its cousin Sr3Ru2O7 is a fully-metallic conductor. Sr3(Ir1-xRux)2O7 undergoes both metal-insulator and antiferromagnetic-paramagnetic transitions across the range of doping. Previous work by this group mapped out the phase diagram, focusing primarily on doping levels up to x=0.4; this project seeks to better understand the region x=0.4 to 0.6, in which at low temperatures the metallic compound settles from paramagnetic disorder into antiferromagnetic order. In the higher-dopant regimes, this also captures the demise of any low-temperature antiferromagnetic order, thus including the yet-unstudied low-temperature end point of the magnetic phase transition. It is possible that a new magnetic or electronic phase could develop in that region. Both the phase transitions and the bulk properties of Sr3(Ir1-xRux)2O7 are items of study. Early work has focused on the flux growth of samples in the desired dopant ranges, XRD and EDX analysis to confirm their composition, and electric transport measurements to begin identifying both metal-insulator and magnetic transitions. Samples of x=0.33 and 0.5 have been successfully grown and characterized, and higher-dopant-level growths are in progress. The approximate phase boundary has been mapped out. An uncommon form of single-crystal XRD is also utilized to obtain the c-lattice (long axis) parameter of the samples, which correlates to their dopant level. Future work will include magnetization and heat capacity measurements, as well as resistivity at sub-Kelvin temperatures.