Frustrated magnetic materials, in which local conditions for energy minimization are incompatible because of the lattice structure, can remain disordered to the lowest temperatures. Such is the case for Ba(3)CuSb(2)O(9), which is magnetically anisotropic at the atomic scale but curiously isotropic on mesoscopic length and time scales. We find that the frustration of Wannier's Ising model on the triangular lattice is imprinted in a nanostructured honeycomb lattice of Cu(2+) ions that resists a coherent static Jahn-Teller distortion. The resulting two-dimensional random-bond spin-1/2 system on the honeycomb lattice has a broad spectrum of spin-dimer-like excitations and low-energy spin degrees of freedom that retain overall hexagonal symmetry.

In a prototypical ferromagnet (Ga,mn)As based on a III-V semiconductor, substitution of divalent mn atoms into trivalent Ga sites leads to severely limited chemical solubility and metastable specimens available only as thin films. The doping of hole carriers via (Ga,mn) substitution also prohibits electron doping. To overcome these difficulties, masek et al. theoretically proposed systems based on a I-II-V semiconductor LiZnAs, where isovalent (Zn,mn) substitution is decoupled from carrier doping with excess/deficient Li concentrations. Here we show successful synthesis of Li 1 + y (Zn 1 − x mn x )As in bulk materials. Ferromagnetism with a critical temperature of up to 50 K is observed in nominally Li-excess (y = 0.05-0.2) compounds with mn concentrations of x = 0.02-0.15, which have p-type metallic carriers. This is presumably due to excess Li in substitutional Zn sites. semiconducting LiZnAs, ferromagnetic Li(Zn,mn)As, antiferromagnetic LimnAs, and superconducting LiFeAs systems share square lattice As layers, which may enable development of novel junction devices in the future.

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