Effective Spin-1/2 Moments on a Yb³⁺ Triangular Lattice: An ESR Study

Abstract

We investigated the spin dynamics by electron spin resonance (ESR) of the Yb-based, effective spin-1/2 delafossites NaYbO 2 , AgYbO 2 , LiYbS 2 , NaYbS 2 , and NaYbSe 2 which all show an absence of magnetic order down to lowest reachable temperatures and thus are prime candidates to host a quantum spin-liquid ground state in the vicinity of long range magnetic order. Clearly resolved ESR spectra allow to obtain well-defined g values which are determined by the crystal field of the distorted octahedral surrounding of the Yb-ions in trigonal symmetry. This local crystal field information provides important input to characterize the effective S = 1/2 Kramers doublet as well as the anisotropic exchange coupling between the Yb ions which is crucial for the nature of the groundstate. The ESR linewidth ∆B is characterised by the spin dynamics and is mainly determined by the anisotropic exchange coupling. We discuss and compare ∆B of the above mentioned delafossites focussing on the low temperature behaviour which is dominated by the growing influence of spin correlations.

Magnetic Properties of an Effective Spin-\(\frac{1}{2}\) Triangular-Lattice Compound LiYbS2

“…The obtained effective moment (µ eff = g S(S + 1)) corresponds to an effective spin-1 2 state with g 2.66. This value matches the powder averaged g av 2.9 from the ESR measurements [18]. The negative value of θ CW indicates a dominant antiferromagnetic nature of exchange interactions between the Yb moments.…”

“…The edge-shared YbS 6 octahedra form the perfect triangular layers of magnetic Yb-ions in the ab-plane, which are well separated by the non-magnetic LiS 6 octahedra along the crystallographic c direction. The local ground state doublet is well separated from the first excited doublet by an energy gap ∆ ∼ 200 K and hence the low-temperature properties can be well described by an effective spin-1 2 state [18].…”

Long-range magnetic order in the ${\tilde S}=1/2$ triangular lattice antiferromagnet KCeS$_2$

“…Specific heat measurements of each of these QSL candidates indicate a broad maximum of C p /T around the temperature corresponding to the possible formation of the spin liquid state [19,22,27,29,30]. This broad maximum is absent in KCeS 2 and replaced by magnetic ordering below T N = 0.38 K. However, it should be emphasized, that despite a different magnetic ground state, KCeS 2 shows strong similarities with the QSL candidates NaYbO 2 , NaYbS 2 and NaYbSe 2 in terms of a well separated S = 1/2 state and a strong easy-plane g-factor anisotropy [19,24,27,66,67]. Thus the open question, which is raised by the present publication is: why does KCeS 2 order magnetically in contrast to many otherS = 1/2 rare-earth based delafossites?…”

Synthesis and Anisotropic Magnetism in Quantum Spin Liquid Candidates $A$YbSe$_2$ ($A$ = K and Rb)

“…[33][34][35][36][37]39,40 The presence of S eff = 1/2 ground state of Yb 3+ based NaYbQ 2 structures at low temperature region is proposed by electron spin resonance, magnetization and neutron scattering measurements. [41][42][43][44][45][46][47] Further, no long-range order has been observed in heat capacity at zero field down to mK temperatures at low magnetic fields. 33,[48][49][50][51][52][53][54][55][56] Quantum disordered or QSL ground state is proposed in NaYbO 2 48,51,57 and the signature of the magnetic excitation continuum has been found in NaYbSe 2 from 0.1 to 2.5 meV in inelastic neutron scattering (INS) measurement, suggesting the ground state of NaYbSe 2 is a QSL with a spinon Fermi surface.…”