Helical order and multiferroicity in the $S=1/2$ quasi-kagome system KCu${}_3$As${}_2$O${}_7$(OD)${}_3$

Abstract

Several Cu${}^{2+}$ hydroxide minerals have recently been identified as candidate realizations of the $S=1/2$ kagome Heisenberg model. In this context, we have studied the distorted system KCu${}_3$As${}_2$O${}_7$(OD)${}_3$ using neutron scattering and bulk measurements. Although the distortion favors magnetic order over a spin liquid ground state, refinement of the magnetic diffraction pattern below $T_{N1}=7.05(5)$ K yields a complex helical structure with $\mathbf{k}=(0.7700.11)$. This structure, as well as the spin excitation spectrum, are well described by a classical Heisenberg model with ferromagnetic nearest neighbor couplings. Multiferroicity is observed below $T_{N1}$, with an unusual crossover between improper and pseudo-proper behavior occurring at $T_{N2}=5.5$ K. The polarization at $T=2$ K is $P=1.5\mu$Cm${}^{-2}$. The properties of KCu${}_3$As${}_2$O${}_7$(OD)${}_3$ highlight the variety of physics which arise from the interplay of spin and orbital degrees of freedom in Cu${}^{2+}$ kagome systems.

Accepted for publication in Phys. Rev. B

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Cited by in corpus (2)

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