Unconventional spin excitations in the S= 32 triangular antiferromagnet RbAg2Cr[VO4]2

Abstract

We present muon spin relaxation (μSR) measurements of the S=3/2 undistorted triangular lattice established in RbAg2Cr[VO4]2. The zero-(ZF) and longitudinal-field μSR spectra evidence the absence of spin freezing and long-range magnetic ordering down to T=25 mK, supporting the formation of a dynamic ground state. Noticeably, we observe an anomalous temperature dependence of the ZF muon spin relaxation rate λZF(T), featuring a decrease below T=20 K. This suggests the alteration of the dominant relaxation mechanism by the development of short-range magnetic correlations. A subsequent leveling off of λZF(T) below T=2 K indicates persistent spin dynamics and reveals the presence of exotic magnetic excitations. The field dependence of the muon spin relaxation rate at T=25 mK is well described by a diffusive spin transport model with algebraic spin-spin correlations. The suppressed long-range order and the peculiar temperature-dependent behavior of λZF(T) will be discussed in terms of the exchange interaction between Cr3+ moments via nonmagnetic [VO4]3- entities. In the title compound, the degeneracy of the t2g-orbital set is not lifted by a space group symmetry reduction or subject to significant anisotropy resulting from spin-orbit coupling. © 2020 American Physical Society.