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Competing interactions in quantum spin systems with geometric frustration can lead to disordered but highly correlated spin states. For decades, experimental research on antiferromagnetic (AFM) quantum kagome materials has been driven primarily by the hunt for the quantum spin liquid (QSL) ground state. The mineral herbertsmithite ZnCu$_3$(OH)$_6$Cl$_2$ stands out from this research on kagome magnetic insulators as a promising QSL candidate with the absence of magnetic order or spin freezing down to mK temperatures [1]. We present here the case of the copper mineral clinoatacamite Cu$_2$Cl(OH)$_3$, a kagome material with a distorted AFM kagome plane in which the competition of symmetry-different AFM ordering modes establishes magnetic frustration at a higher level and leads to complex magnetic behavior.
Structurally, clinoatacamite is closely related to the QSL candidate herbertsmithite, however, its kagome motif of Cu sites is embedded into a low-symmetry crystal structure with different symmetries for the kagome sites. The magnetic ground states of clinoatacamite below an ordering temperature of 18.1 K have remained inconclusive in the past (see, for instance, Ref. [2]). Here, we revisit the magnetic properties using single-crystalline material. We have characterized clinoatacamite by means of thermodynamic measurement techniques, muon spin rotation/relaxation as well as by neutron diffraction. We find in multicritical clinoatacamite a complex zero-field sequence of phases and discuss our data within a scenario of competing even-odd AFM ordering modes [3].
[1] P. Mendels et al., Phys. Rev. Lett. 98, 077204 (2007).
[2] X. G. Zheng et al., Phys. Rev. Lett. 95, 057201 (2005).
[3] L. Stödter et al., Phys. Rev. Lett. 137, 116701 (2026).