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

Abstract

Recently, several putative quantum spin liquid (QSL) states were discovered in {\tilde S} = 1/2S̃=1/2 rare-earth based triangular-lattice antiferromagnets (TLAF) with the delafossite structure. In order to elucidate the conditions for a QSL to arise, we report here the discovery of a long-range magnetic order in the Ce-based TLAF KCeS_22 below T_{\mathrm N} = 0.38TN=0.38 K, despite the same delafossite structure. Finally, combining various experimental and computational methods, we characterize the crystal electric field scheme, the magnetic anisotropy and the magnetic ground state of KCeS_22.

Magnetic properties and signatures of moment ordering in triangular lattice antiferromagnet KCeO$_2$

“…While an antiferromagnetic Θ CW = −7.7 K from Curie-Weiss analysis indicates a strong degree of magnetic frustration, a second, sharp peak in the low-temperature specific heat combined with lowenergy INS data showing multi-branch spin excitations at 40 mK indicate a magnetically ordered ground state. This observation is consistent with a recent report of long-range magnetic order in the sulfur-based analog KCeS 2 [79]. Although no new magnetic Bragg peaks were observed in elastic neutron scattering data collected at 300 mK for KCeO 2 , the likely reason is that the ordered moment is below the limit detection in current measurements.…”

“…multiple local environments [25,[69][70][71][72][79][80][81]. Somewhat uniquely, none of these explanations adequately explain the origin of the E 3 mode in KCeO 2 .…”

“…This considerably weakens the possibility that the extra mode at 170 meV arises from a transition into a J = 7/2 state. Anomalous CEF modes observed for lanthanide ions in similar crystallographic environments are often explained by invoking coupling to phonons or vibronic effects [66][67][68][69][70][71][72], conjectures of hydrogen embedded within the sample [73][74][75][76][77][78][79], or the potential presence of chemical impurities creating…”

“…Second, while hydrogen impregnation is another potential source of unexplained CEF transitions in materials [73][74][75][76][77][78][79], the synthesis of KCeO 2 requires strict atmospheric handling in an inert glove box environment. A significant concentration of hydrogen would be required to generate the spectral weight at E 3 and is unlikely to generate the sharp energy line width observed.…”

Fingerprinting triangular-lattice antiferromagnet by excitation gaps

“…This study is of immediate relevance to KCeS 2 [46], KErSe 2 [47], and isostructural CeCd 3 P 3 [48], where some of the same phenomenology has been observed. Future studies by thermodynamic and spectroscopic methods, such as low-T magnetization, nuclear and electronic magnetic resonance, neutron and x-ray magnetic dichroism scattering, are expected to provide further insights into the nature of the crossover region in the H-T phase diagram and into the role of structural disorder in the static and dynamic properties of these materials.…”