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

Abstract

It is demonstrated that novel spin frustration can be induced in ferromagnets with nonuniform Land\'{e} $g$-factors. The frustrated state is characterized by a mutual interplay of typical ferromagnetic (FM) and antiferromagnetic (AF) features, such as the zero-field susceptibility being FM-like at low temperatures but AF-like at high temperatures. It is also found to contain an exotic zero-temperature `half fire, half ice' critical point at which the spins on 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 oxides such as Sr$_3$CuIrO$_6$. We also anticipate a realization of the frustration and `partial fire, partial ice' states in certain antiferromagnets, lattice gas, and neuron systems.