Spangolite: ans= 1/2 maple leaf lattice antiferromagnet?

Abstract

Spangolite, Cu 6 Al(SO 4 )(OH) 12 Cl·3H 2 O, is a hydrated layered copper sulfate mineral. The Cu 2+ ions of each layer form a systematically depleted triangular lattice which approximates a maple leaf lattice. We present details of the crystal structure, which suggest that in spangolite this lattice actually comprises two species of edge linked trimers with different exchange parameters. However, magnetic susceptibility measurements show that despite the structural trimers, the magnetic properties are dominated by dimerization. The high temperature magnetic moment is strongly reduced below that expected for the six s = 1/2 in the unit cell.

Spin-half Heisenberg antiferromagnet on two archimedian lattices: From the bounce lattice to the maple-leaf lattice and beyond

“…These rather small values of the order parameter, which are significantly below that for the triangular lattice, 4,[12][13][14][15][16] indicate that the GS magnetic LRO is fragile, and one can speculate that slight modifications of the model parameters might lead to non-magnetic quantum GSs. We remark again that a related experimental material called spangolite 43 did not appear to shown magnetic LRO, and that this experimental result also spurs us on to evaluate the more general model. The extrapolated values in the limit n → ∞ are found using the extrapolation scheme Ms(n) = c0 + c1(1/n) + c2(1/n) 2 .…”

“…This antiferromagnetic system is geometrically frustrated and it is related to several magnetic materials which have been experimentally investigated recently. 40,41,43 On the classical level the ground state is a commensurate non-collinear antiferromagnetic state. To study the quantum GS of the spin-half model we use the CCM for infinite lattices and the ED for finite lattices of N = 18 and N = 36 sites.…”

“…42,43 In particular, spangolite is a very interesting magnetic system, since magnetic copper ions carry spin 1/2 and the experimental data indicate that strong fluctuations at low temperatures are present which may prevent magnetic ordering. 43 In Ref. 43 Fennell et al propose that the spin-half Heisenberg model on the maple-leaf lattice with five different exchange integrals is the relevant model for this material.…”

Quantum magnetism in minerals

“…However, none of these minerals has been so far grown artificially in the form of single crystals, and the number of published lowtemperature studies of their magnetic properties remains very limited. In 2011, Fennell et al [578] presented the results of a structural and basic magnetic characterization of the layered…”

“…48. The application of GKA rules to the spangolite structure suggests that the superexchange interactions J 1 and J 2 within both trimers must be antiferromagnetic, resulting in a strong frustration [578]. The trimers are coupled with AFM interactions J 3 , J 4 , and a FM interaction J 5 along different exchange paths shown in Fig.…”