NZAO Hexaaluminate Exhibits Persistent Magnetic Fluctuations Without Ordering to Millikelvin Temperatures

The search for materials exhibiting exotic magnetic behaviour has led researchers to investigate compounds with specific atomic arrangements, such as triangular lattices, which can give rise to unusual quantum states. Yantao Cao from the Institute of Physics, Chinese Academy of Sciences, Huanpeng Bu from Songshan Lake Materials Laboratory, and Toni Shiroka from PSI Center for Neutron and Muon Sciences CNM, alongside their colleagues, have been studying a material called neodymium zinc aluminium oxide to explore this possibility. Their work reveals a complex magnetic ground state with persistent fluctuations that do not freeze even at extremely low temperatures, suggesting the material may host a spin liquid state , a phase of matter where magnetic moments remain disordered despite the cold, potentially enabling novel technologies. This discovery is significant because spin liquids are rare and offer a pathway to understanding fundamental quantum phenomena and developing new quantum materials.

Triangular Lattices and Quantum Spin Liquid Search

A quantum spin liquid (QSL) represents an intriguing state of matter where electronic spins interact strongly, yet avoid conventional magnetic ordering due to significant quantum fluctuations. Triangular-lattice antiferromagnets are considered promising platforms for discovering these exotic states, as theoretical models predict specific ordering under certain conditions, though interactions or anisotropy may instead give rise to a spin liquid state. Recent studies on neodymium heptatantalate and layered rare-earth hexaaluminate R(Mg/Zn)Al11O19 have revealed a tendency for spins to align, with CeMgAl11O19 exhibiting a strong preference for alignment along a specific direction. The ability to grow large, high-quality single crystals of the magnesium-containing system is a key advantage for detailed study.

This work reports a comprehensive study of polycrystalline NdZnAl11O19 using magnetic susceptibility, inelastic neutron scattering, and muon spin relaxation. Compared to isostructural CeMgAl11O19, this compound exhibits weaker alignment of spins, but still demonstrates a moderate preference for alignment. The large energy gap of the first crystal-electric-field excitation simplifies the model used to describe its low-temperature properties. The system displays persistent spin fluctuations below approximately 15 K, but no magnetic ordering or spin freezing down to 50 mK, establishing it as a plausible candidate for realizing a QSL state.

NdZnAl11O19 Magnetic Properties and Anisotropy

This research details a comprehensive investigation into the magnetic properties of NdZnAl11O19, a material potentially hosting a quantum spin liquid (QSL) state. Key findings include a preference for spins to align in a specific direction, reflected in a g-factor ratio of approximately 3.2, and a ground state dominated by a specific spin orientation revealed by crystal field analysis. Weak antiferromagnetic coupling is also observed, indicated by a Curie-Weiss temperature of -0.42 K, suggesting frustration. Neutron scattering reveals minimal disorder, while AC susceptibility measurements show no transition to a spin glass state down to 50 mK.

Muon spin relaxation (μSR) measurements reveal persistent dynamic spin fluctuations even at very low temperatures, an Orbach process involving the first crystal field excited state, and motional narrowing confirming fast spin fluctuations. A plateau in the relaxation rate at low temperatures further suggests the persistence of fluctuations. The combination of weak interactions, frustration, and persistent dynamic spin fluctuations points towards a QSL state. The strong preference for directional alignment may favor a particular type of QSL, and the lack of significant disorder strengthens the possibility of intrinsic QSL behavior. Further investigation with single crystals is needed to confirm this hypothesis and characterize the nature of the QSL state.

Laser Tuning Yields Diamond-Like Silicon Carbide Films

This work details a detailed investigation into the behaviour of amorphous silicon carbide films deposited using pulsed laser deposition. Controlling the laser energy and substrate temperature allows precise tuning of the film’s composition and structural properties. Films grown at a laser energy of 0.8 J/cm² and a substrate temperature of 600 °C exhibit a silicon-to-carbon ratio of 1:1 and a density of 2.8 g/cm³, closely matching that of crystalline silicon carbide. Raman spectroscopy confirms the formation of strong chemical bonds, indicating a diamond-like structure, and the films display a hardness of 25 GPa and a Young’s modulus of 220 GPa. These properties suggest potential applications in protective coatings, microelectronics, and high-frequency devices. Further research focuses on reducing the hydrogen content within the films to enhance their thermal stability and electrical conductivity, and exploring the scalability of the process for large-area production.