Studies of the itinerant metamagnet strontium ruthenate
Description
The strontium ruthenate Sr3Ru2O 7 is a strongly correlated electron system with intriguing electronic and magnetic properties. Though structurally similar to the widely studied unconventional superconductor Sr2RuO4, its properties are quite different: its ground state appears to be close to a ferromagnetic instability. Moderate applied magnetic fields can induce a metamagnetic transition into a ferromagnetic-like state, defined as a superlinear rise in magnetization at a given value of applied field; there is good evidence that this transition is a zero-temperature quantum phase transition with features distinctly different than ordinary phase transitions. We have taken three avenues towards better understanding the electronic and magnetic properties of Sr3Ru 2O7 and its behavior under magnetic fields: single particle tunneling, doping with nonmagnetic Ti impurities, and critical current measurements of a Sr2RuO4-Sr3Ru2O7 intergrowth Our tunneling measurements reveal an unusual oscillation in tunneling magnetoresistance under applied magnetic fields. This behavior is unexpected within our existing understanding of Sr3Ru2O7, and likely indicates the presence of an unusual surface state on this material. Our studies of Ti doped Sr3Ru2O7 suggest that the ground state of this material is characterized by competing short-range ferromagnetic and antiferromagnetic interactions; nonmagnetic Ti impurities appear to alter the band structure in such a way to reduce the antiferromagnetism, leaving the system in a state dominated by 2D ferromagnetic fluctuations. Finally, our studies of the Sr2RuO4-Sr3Ru 2O7 solid mixture suggest that large regions of Sr3 Ru2O7 may become superconducting when intergrown in this fashion; this finding may also shed light on the pairing mechanism of the unconventional superconductor Sr2RuO4 These three approaches to studying the ground state of the itinerant metamagnet Sr3Ru2O7 reveal the great diversity of electronic and magnetic properties possible in this material. In addition to confirming key issues related to the magnetic ground state, our results suggest several new directions for further study of Sr3Ru 2O7 and related strontium ruthenate materials