Low-temperature specific-heat studies on two square-kagome antiferromagnets

New Nabokoite‐like Phases ACu7TeO4(SO4)5Cl (A=Na, K, Rb, Cs) with Decorated and Distorted Square Kagome Lattices

“…Our previous study of the low‐temperature specific heat in KCu 6 AlBiO 4 (SO 4 ) 5 Cl and Na 6 Cu 7 BiO 4 (PO 4 ) 4 Cl 3 provided the key information that the existence of interlayer Cu 2+ ions has negligible effects on the magnetic system of the SKL layers [36] . The low‐temperature specific heats of these compounds under magnetic field are quite similar, suggesting that independent on the presence of idle Cu2 in the structure both ideal non‐decorated and distorted decorated systems are suitable to investigate the SKL model.…”

“…For two decades since prediction of SKL properties in 2001, the investigation of such a system has been restricted to theoretical insights only [18–33] . Quite recently, experimental studies on KCu 6 AlBiO 4 (SO 4 ) 5 Cl [34] and Na 6 Cu 7 BiO 4 (PO 4 ) 4 Cl 3 [35] have been performed, which evidenced, however, neither spin gap nor its specific heat signature [36] . The contradiction between theory and experiment stimulates further search for the layered compounds with the square kagome patterns.…”

“…[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] Quite recently, experimental studies on KCu 6 AlBiO 4 (SO 4 ) 5 Cl [34] and Na 6 Cu 7 BiO 4 (PO 4 ) 4 Cl 3 [35] have been performed, which evidenced, however, neither spin gap nor its specific heat signature. [36] The contradiction between theory and experiment stimulates further search for the layered compounds with the square kagome patterns. Here, we present the systematic study of newly prepared compounds with the mineral Nabokoite structure ACu 7 (TeO 4 )(SO 4 ) 5 Cl (A = Na, K, Rb, Cs).…”

Non-Coplanar Magnetic Orders in Classical Square-Kagome Antiferromagnets

“…In the context of material realizations, it is worth noting that in Na 6 Cu 7 BiO 4 (PO 4 ) 4 [Cl,(OH)] 3 [20], the J × interactions are mediated by Cu-O-Na-O-Cu superexchange path-ways, while the J + bonds pass through a chloride group but distances that prevent any Cu-Cl hybridization, and thus not triggering a superexchange. The presence of the nonmagnetic Na ions in the center of the octagons is likely to trigger a finite J × interaction akin to the scenario realized in the kagome based materials kapellasite and haydeeite [52].…”

“…An ideal playground to explore this physics in experiment has come in the arrival of materials based on the novel square-kagome lattice geometry [17], whose potential to host intricately textured magnetic ground states or quantum spin liquid phases is currently under much investigation [18]. Indeed, no sign of long-range magnetic order down to 50 mK has been observed in the spin S = 1/2 Cu 2+ based materials KCu 6 AlBiO 4 (SO 4 ) 5 Cl [19] and Na 6 Cu 7 BiO 4 (PO 4 ) 4 [Cl,(OH)] 3 [20] despite having large negative Curie-Weiss temperatures of −237 K and −212 K, respectively. On the other hand, their sister compound KCu 7 (TeO 4 )(SO 4 ) 5 Cl presumably orders into a non-collinear antiferromagnetic structure [21].…”