Unexpected magnetic properties of gas-stabilized platinum nanostructures in the tunneling regime.

Nanostructured materials often have properties widely different from bulk, imposed by quantum limits to a physical property of the material. This includes, for example, superparamagnetism and quantized conductance, but original properties such as magnetoresistance in nonmagnetic molecular structures may also emerge. In this Letter, we report on the atomic manipulation of platinum nanocontacts in order to induce magnetoresistance. Platinum is a paramagnetic 5d metal, but atomic chains of this material have been predicted to be magnetically ordered with a large anisotropy. Remarkably, we find that a gas flow stabilizes Pt atomic structures in a break junction experiment, where we observe extraordinary resistance changes over 30,000% in a temperature range up to 77 K. Simulations indicate that this behavior may stem from a previously unknown magnetically ordered, low-energy state in platinum oxide atomic chains. This is supported by measurements in Pt/PtOx superlattices revealing the presence of a ferromagnetic moment. These properties open new paths of research for atomic scale "dirty" magnetic sensors and quantum devices.