Spin Frustration and a `half Fire, Half Ice' Critical Point from Nonuniform G-Factors

It is demonstrated that novel spin frustration can be induced in ferromagnetswith nonuniform Landé g-factors. The frustrated state is characterized bya mutual interplay of typical ferromagnetic (FM) and antiferromagnetic (AF)features, such as the zero-field susceptibility being FM-like at lowtemperatures but AF-like at high temperatures. It is also found to contain anexotic zero-temperature `half fire, half ice' critical point at which the spinson one sublattice are fully disordered and on the other one are fully ordered.We suggest that such frustration may occur in a number of copper-iridium oxidessuch as Sr_3CuIrO_6. We also anticipate a realization of the frustrationand `partial fire, partial ice' states in certain antiferromagnets, latticegas, and neuron systems.