Emergent spin-glass behavior created by chemical doping and self-assembly in transition-metal oxides*

Spin glass is a magnetic state with a spin structure incommensurate with lattice and charge. A fundamental understanding of its behavior has a profound impact on many technological problems. Here, we present two novel cases with (1) chemical doping in layered Sr₃(Ru_1-xMn_x)₂O₇ and (2) self-assembly of single-crystalline NiO micro-columns in a single-crystalline NiFe₂O₄ matrix. In addition to the memory effect reflected in the magnetic susceptibility, transmission electron microscopy provides information about dopant distribution and atomic arrangement at the interface. The atomic-level characterization enables us to elucidate the origin of spin-glass (SG) behavior in both systems, which results from spin disorder and frustration. Our results demonstrate effective ways to create novel spin states in transition-metal oxides.