Properties of spin-12triangular-lattice antiferromagnetsCuY2Ge2O8and

Hwanbeom Cho

¹

,

Marie Kratochvílová

²

,

Hasung Sim

³

et al.

Abstract

Keyword: low-dimensional quantum spin system, geometrical frustration, magnetic long-range order, field induced phase transition, charge transfer insulator.PACS Numbers: 75.10.Jm, 75.30.Kz, Abstract: We found new two-dimensional (2D) quantum (S=1/2) antiferromagnetic systems: CuRE2Ge2O8 (RE=Y and La).According to our analysis of high-resolution X-ray and neutron diffraction experiments, the Cu-network of CuRE2Ge2O8 (RE=Y and La) exhibits a 2D triangular lattice linked via weak bonds along the perpendicular b-axis. Our bulk characterizations from 0.08 to 400 K show that they undergo a long-range order at 0.51(1) and 1.09(4) K for the Y and La systems, respectively. Interestingly, they also exhibit field induced phase transitions. For theoretical understanding, we carried out the density functional theory (DFT) band calculations to find that they are typical charge-transfer-type insulators with a gap of Eg ≅ 2 eV. Taken together, our observations make CuRE2Ge2O8 (RE=Y and La) additional examples of low-dimensional quantum spin triangular antiferromagnets with the lowtemperature magnetic ordering.

Frustrated antiferromagnetic honeycomb-tunnel-like latticeCuR2Ge2O8(R=Pr, Nd, S

“…We collected altogether 2889 Bragg peaks (1860 independent Bragg peaks). The crystal structure was refined using the I 1 m 1 unit cell setting of the nonmagnetic rare-earth analog [38]. The unit cell size is a( (9), and V ( Å3 )=661.2(3).…”

“…Fig. 2 shows the refined crystal structure of the CuNd 2 Ge 2 O 8 system, which is isostructural with other rare-earth systems including the nonmagnetic rare-earth analog Cu(Y/La) 2 Ge 2 O 8 [38]. The unit cell size and monoclinic β angle vary depending on the ionic size of RE 3+ [39].…”

“…The unit cell size and monoclinic β angle vary depending on the ionic size of RE 3+ [39]. In the previous study of nonmagnetic rareearth cases [38], the magnetism of the system was characterized by the Cu-ion coordination since Cu is the only magnetic element present in the compound. For magnetic rare-earth cases, however, the magnetism is instead expected to be affected significantly by the large magnetic moments of rare-earth ions.…”

“…(here, µ ef f,total is the total effective moment from the Curie constant C and µ ef f,Cu is the effective moment of Cu [38]). For our fitting of the Pr and Nd compounds, we used the data taken above 100 K. The respective ordering temperatures, the experimental and reference effective moments of RE 3+ [47], and the Curie-Weiss temperatures are summarized in TABLE II.…”

Magnetic excitations of the Cu2+ quantum spin chain in Sr3CuPtO6

“…3(i) and 3(j). An explanation for this behavior may come from a theoretical study by Kohno et al [38] which considers the spin excitation spectra of 2D triangular lattice compounds, such as Cs 2 CuCl 4 [39] and Cu(Y/La) 2 Ge 2 O 8 [40], with magnetic couplings close to the limit of 1D spin chains. Kohno et al showed that (FM or AFM) interchain interactions between the 1D spin chains introduces an (attractive or repulsive) force between spinons, resulting in delocalized composite particles called (bound or anti-bound) triplons which can move coherently between chains [41].…”