Kagome quantum spin systems in the atacamite family

Abstract

We present the hydrothermal synthesis, as well as structural and chemical analysis of single crystals on the compounds EuCu3(OH)6Cl3, ZnxCu4−x(OH)6(NO3)2 and haydeeite, MgCu3(OH)6Cl2 all arising from the atacamite family. Magnetic and specific-heat measurements down to 1.8 K are carried out for these systems. EuCu3(OH)6Cl3 has a frustrated antiferromagnetic Cu 2+ ground state with order at 15 K, a strong anisotropy and increased magnetization from Van Vleck paramagnetic Eu 3+ contributions. ZnCu3(OH)6(NO3)2 reveals antiferromagnetic order at 9 K and measurements on haydeeite single crystals confirm the ferromagnetic order at 4.2 K with the easy axis within the kagome plane. These results prove that the atacamite family presents a broad class of materials with interesting magnetic ground states.

Tuning of a Kagome Magnet: Insulating Ground State in Ga‐Substituted Cu4(OH)6Cl2

“…But even at the highest possible molar ratios, which still lead to the proper phase, the average Ga content stays below x = 1 (see Table ), which could be ascribed to the fact that the herbertsmithite‐type structure is not stable with a full additional OH/Cl − molecule/atom. This is further being supported by the other cases with a trivalent atom on the Cu site, which realize the kapellasite type structure at only and exactly …”

“…Unlike other trivalent ions, which all realize the kapellasite type structure the compounds Ga x Cu 4 –x (OD) 6 Cl 2 show similar PXRD patterns as for Zn substitutions. Thus Ga x Cu 4 –x (OD) 6 Cl 2 has a similar structure as clinoatacamite and herbertsmithite.…”

“…This scenario is supported by the fact that in most EDX images for , the Ga content is lower than the stoichiometric ratio, but it is in contrast to the observation of magnetic order in the sample, since in herbertsmithite at the order is already suppressed and with vacancies on the interlayer site less substitution might be necessary to expel Cu on this position between the kagome layers. A different possible scenario is, that the additional electron is balanced by additional Cl or OH, but not in a stoichiometric manner, as observed in EuCu 3 (OH) 6 Cl 3 and YCu 3 (OH) 6 Cl 3 , but more likely in a mixed form, e.g., as Ga x Cu 4 –x (OD) 6+2 x /3 Cl 2+ x /3 , which then is more difficult to detect in EDX and X‐ray diffraction, because the determination of the oxygen is not as accurate as for Cl. From the average over many EDX measurements we see systematically an increased O and Cl content, as discussed in section 5.…”

“…When replacing divalent Zn by trivalent Y, Eu, Nd etc . the additional electron is either bound to additional OH − or Cl − anions and the kapellasite type structure is realized . A direct doping attempt by intercalating Li into herbertsmithite also does not lead to metallic behavior but instead strong Anderson localization of the additional charge carriers was reported …”

Coexistence of magnetic order and persistent spin dynamics in a quantum kagome antiferromagnet with no intersite mixing

“…Other QKA spinliquid candidates, like tondiite MgCu 3 (OH) 6 Cl 2 [20], Zn-brochantite ZnCu 3 (OH) 6 SO 4 [21], and Zn-barlowite ZnCu 3 (OH) 6 FBr [22] suffer from a very similar amount of magnetic/non-magnetic ion mixing. Such mixing can in principle be reduced by introducing larger non-magnetic ions, like in the cases of CaCu 3 (OH) 6 Cl 2 · 0.7H 2 O [23] and EuCu 3 (OH) 6 Cl 3 [24], which however both order magnetically. A similar situation is encountered in Ga x Cu 4−x (OD) 6 Cl 2 , where frozen magnetic moments persist up to the highest substitution level (x = 0.8) [25].…”