Quantum magnetisms in uniform triangular lattices Li2AMo3O8 (A\u2009=\u2009In, Sc)

Kazuki Iida,Hiroyuki Yoshida,Ryoichi Kajimoto,Hirotaka Okabe,Ryosuke Kadono,Yuto Ishii,Motoyuki Ishikado,Yasuhiro Inamura,Naoki Murai,Naoyuki Katayama,Akihiro Koda

doi:10.1038/s41598-018-36123-7

Abstract

Molecular based spin-1/2 triangular lattice systems such as LiZn2Mo3O8 have attracted research interest. Distortions, defects, and intersite disorder are suppressed in such molecular-based magnets, and intrinsic geometrical frustration gives rise to unconventional and unexpected ground states. Li2AMo3O8 (A = In or Sc) is such a compound where spin-1/2 Mo3O13 clusters in place of Mo ions form the uniform triangular lattice. Their ground states are different according to the A site. Li2InMo3O8 undergoes conventional 120° long-range magnetic order below TN = 12 K whereas isomorphic Li2ScMo3O8 exhibits no long-range magnetic order down to 0.5 K. Here, we report exotic magnetisms in Li2InMo3O8 and Li2ScMo3O8 investigated by muon spin rotation (μSR) and inelastic neutron scattering (INS) spectroscopies using polycrystalline samples. Li2InMo3O8 and Li2ScMo3O8 show completely different behaviors observed in both μSR and INS measurements, representing their different ground states. Li2InMo3O8 exhibits spin wave excitation which is quantitatively described by the nearest neighbor anisotropic Heisenberg model based on the 120° spin structure. In contrast, Li2ScMo3O8 undergoes short-range magnetic order below 4 K with quantum-spin-liquid-like magnetic fluctuations down to the base temperature. Origin of the different ground states is discussed in terms of anisotropies of crystal structures and magnetic interactions.

Highlights

When quantum spins are aligned on geometrically frustrated lattices, unusual ground state eventually emerges among energetically competed states[1,2,3]
We investigate quantum magnetisms of polycrystalline Li2InMo3O8 and Li2ScMo3O8 by combination of μSR and time-of-flight (TOF) neutron scattering techniques
3.33 K [see the inset of Fig. 2(a)] suggests that at least three different local fields are found in Li2InMo3O8, which is probably due to crystallographically inequivalent muon stopping sites indicated by our density functional theory (DFT) calculation

Summary

Introduction

When quantum spins are aligned on geometrically frustrated lattices, unusual ground state eventually emerges among energetically competed states[1,2,3]. Extensive experimental studies have been conducted on spin-1/2 TLHAFs; the 120° long-range magnetic order is reported in Ba3CoSb2O912–14 whereas QSL state is proposed for the ground states of κ-(BEDT-TTF)2Cu2(CN)[315,16], EtMe3Sb[Pd(dmit)2]217,18, YbMgGaO419–22 and 1T-TaS223. Susceptibility measurements of both compounds report that the dominant magnetic interactions are antiferromagnetic and the effective moments are 1.61 μB (In) and 1.65 μB (Sc), which are close to peff = 1.73 μB the ideal value for spin S = 1/2. We investigate quantum magnetisms of polycrystalline Li2InMo3O8 and Li2ScMo3O8 by combination of μSR and time-of-flight (TOF) neutron scattering techniques

Methods

Results

Conclusion