Rubidium Ytterbium Vanadate Reveals Potential for Quantum Spin Liquid Behaviour

Research on RbYb(VO₄) confirms a Kramers’ doublet ground state and weak antiferromagnetic interactions, with no long-range magnetic order detected down to 1.6 K. Calculations reveal a significant energy gap between ground and excited states and indicate in-plane magnetic anisotropy, suggesting potential for exploring spin-liquid behaviour.

The search for novel quantum states of matter continues to drive research into materials exhibiting strong correlations between electrons. Triangular lattice antiferromagnets, where magnetic moments align in opposing directions on a triangular arrangement, are particularly interesting as they frequently frustrate conventional magnetic ordering, potentially leading to exotic phases such as quantum spin liquids. A recent investigation, detailed in the article ‘Spin fluctuations, absence of magnetic order, and crystal electric field studies in the Yb-based triangular lattice antiferromagnet RbYb(VO₄)’, reports on the properties of this material, revealing a system dominated by fluctuations rather than static magnetic order.

The work, conducted by Sebin J. Sebastian, R. Kolay, Abhidev. B. from the School of Physics, Indian Institute of Science Education and Research Thiruvananthapuram, alongside Q.-P. Ding and Y. Furukawa from Ames National Laboratory, and R. Nath from the Indian Institute, utilises a combination of experimental techniques and theoretical calculations to characterise the magnetic behaviour of RbYb(VO₄). Their findings suggest this material represents a promising platform for exploring the fundamental physics of quantum magnetism and potentially realising spin-liquid behaviour.

Investigating Fluctuating Magnetism in RbYb(VO₄)

RbYb(VO₄) exhibits characteristics suggestive of a fluctuating magnetic ground state, potentially hosting exotic spin-liquid behaviour. A comprehensive investigation into the structural, static, and dynamic magnetic properties of this triangular lattice antiferromagnet has yielded insights into its magnetic ground state and potential for hosting unconventional quantum phenomena.

Detailed analysis of magnetic susceptibility, magnetisation, and specific heat capacity, alongside crystal electric field (CEF) calculations, confirmed the existence of a Kramers’ doublet – a pair of degenerate energy levels – establishing a foundation for understanding the material’s unique magnetic behaviour. The observed weak antiferromagnetic interactions between spins are characterised by a small Curie-Weiss temperature (Θ ≈ -2.5 K) or a reduced exchange coupling (J ≈ 1.5 meV), indicating a delicate balance between competing magnetic tendencies.

⁵¹V Nuclear Magnetic Resonance (NMR) spectroscopy was employed to probe the local magnetic environment of the vanadium ions and investigate the magnetic interactions between the Yb³⁺ and V³⁺ ions. The resulting spectra exhibited a broad resonance line, indicative of a wide distribution of local magnetic fields. Analysis of the ⁵¹V NMR spectra determined the Knight shift – a measure of the local magnetic field at the vanadium nucleus – revealing a temperature dependence consistent with magnetic interactions between the Yb³⁺ and V³⁺ ions.

Measurements of the spin-lattice relaxation rate (1/T₁) investigated the dynamics of local magnetic fields and probed magnetic interactions between the Yb³⁺ ions. The temperature dependence of the 1/T₁ data indicates the presence of magnetic fluctuations, allowing for the determination of their correlation time and an estimation of the interaction strength.

Specific heat capacity measurements, performed across a wide temperature range, investigated the thermal properties of RbYb(VO₄) and searched for evidence of magnetic phase transitions. A broad peak observed at approximately 50 K, consistent with the maximum in the magnetic susceptibility measurements, suggests short-range magnetic correlations. The absence of a sharp peak indicates the lack of a conventional magnetic phase transition, supporting the notion of weak and frustrated magnetic interactions.

Isothermal magnetisation measurements at various temperatures investigated the material’s magnetic behaviour in a magnetic field. The observed linear response at high fields indicates the absence of magnetic saturation and the presence of weak magnetic moments. Slight curvature in the low-temperature magnetisation curves suggests the presence of short-range magnetic correlations and the influence of quantum fluctuations.

Further magnetic susceptibility measurements in different magnetic fields provided additional insights into the magnetic interactions and the nature of the magnetic ground state, reinforcing the evidence for short-range correlations and the absence of long-range magnetic order.