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1. Quantum liquid from strange frustration in the trimer magnet Ba4Ir3O10

   https://doi.org/10.1038/s41535-020-0232-6  

   Cao, Gang ; Zheng, Hao ; Zhao, Hengdi ; Ni, Yifei ; Pocs, Christopher A. ; Zhang, Yu ; Ye, Feng ; Hoffmann, Christina ; Wang, Xiaoping ; Lee, Minhyea ; et al ( May 2020 , npj Quantum Materials)

   Quantum spin systems such as magnetic insulators usually show magnetic order, but such classical states can give way toquantum liquids with exotic entanglementthrough two known mechanisms of frustration: geometric frustration in lattices with triangle motifs, and spin-orbit-coupling frustration in the exactly solvable quantum liquid of Kitaev’s honeycomb lattice. Here we present the experimental observation of a new kind of frustrated quantum liquid arising in an unlikely place: the magnetic insulator Ba₄Ir₃O₁₀where Ir₃O₁₂trimers form an unfrustrated square lattice. The crystal structure shows no apparent spin chains. Experimentally we find a quantum liquid state persisting down to 0.2 K that is stabilized by strong antiferromagnetic interaction with Curie–Weiss temperature ranging from −766 to −169 K due to magnetic anisotropy. The anisotropy-averaged frustration parameter is 2000, seldom seen in iridates. Heat capacity and thermal conductivity are both linear at low temperatures, a familiar feature in metals but here in an insulator pointing to an exotic quantum liquid state; a mere 2% Sr substitution for Ba produces long-range order at 130 K and destroys the linear-T features. Although the Ir⁴⁺(5d⁵) ions in Ba₄Ir₃O₁₀appear to form Ir₃O₁₂trimers of face-sharing IrO₆octahedra, we propose that intra-trimer exchange is reduced and the lattice recombines into an array of coupled 1Dmore »chains with additional spins. An extreme limit of decoupled 1D chains can explain most but not all of the striking experimental observations, indicating that the inter-chain coupling plays an important role in the frustration mechanism leading to this quantum liquid.

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2. Signature of a randomness-driven spin-liquid state in a frustrated magnet

   https://doi.org/10.1038/s42005-022-00879-2  

   Khatua, J. ; Gomilšek, M. ; Orain, J. C. ; Strydom, A. M. ; Jagličić, Z. ; Colin, C. V. ; Petit, S. ; Ozarowski, A. ; Mangin-Thro, L. ; Sethupathi, K. ; et al ( April 2022 , Communications Physics)

   Collective behaviour of electrons, frustration induced quantum fluctuations and entanglement in quantum materials underlie some of the emergent quantum phenomena with exotic quasi-particle excitations that are highly relevant for technological applications. Herein, we present our thermodynamic and muon spin relaxation measurements, complemented by ab initio density functional theory and exact diagonalization results, on the recently synthesized frustrated antiferromagnet Li₄CuTeO₆, in which Cu²⁺ions (S= 1/2) constitute disordered spin chains and ladders along the crystallographic [101] direction with weak random inter-chain couplings. Our thermodynamic experiments detect neither long-range magnetic ordering nor spin freezing down to 45 mK despite the presence of strong antiferromagnetic interaction between Cu²⁺moments leading to a large effective Curie-Weiss temperature of − 154 K. Muon spin relaxation results are consistent with thermodynamic results. The temperature and magnetic field scaling of magnetization and specific heat reveal a data collapse pointing towards the presence of random-singlets within a disorder-driven correlated and dynamic ground-state in this frustrated antiferromagnet.
3. The disordered and correlated insulator Bi2CrAl3O9

   https://doi.org/https://doi-org.ezproxy.library.ubc.ca/10.1103/PhysRevB.100.104425  

   Umana, J. C. ; Baccarella, A. M. ; Steinke, L ; Geritano, A ; Janssen, Y. ; Aronson, M. C ; Simonson, J. W. ( September 2019 , PRB)

   The 3d transition metal insulator Bi2CrAl3O9 forms with a quasi-one-dimensional structure characterized by linear chains of edge-sharing, Cr-and Al-centered, distorted octahedra. The UV/Vis spectrum of high-quality single crystals is marked by broad absorption edges corresponding to direct transitions across a 1.36-eV insulating gap. Measurements of dc magnetic susceptibility χ reveal a fluctuating moment of 2.60±0.01μB/Cr—reduced from the 3.87μB/Cr expected for Cr3+, while the Weiss temperature ΘW=−21±1 K implies that the prevailing local moment interactions are weakly antiferromagnetic in nature. Some 10% of the fluctuating moment is quenched, presumably due to the onset of an antiferromagnetic or spin glass phase at temperature T★=98±3 K, while measurements of magnetization versus field H at T≤10 K scale as H/T0.68(4), suggesting the presence of quantum fluctuations associated with a disordered phase. Density functional theory calculations carried out within the generalized gradient approximation are in excellent agreement with experimental results, asserting that short-range magnetic interactions remnant above T★ stabilize the insulating state
4. Single crystal neutron and magnetic measurements of Rb ₂ Mn ₃ (VO ₄ ) ₂ CO ₃ and K ₂ Co ₃ (VO ₄ ) ₂ CO ₃ with mixed honeycomb and triangular magnetic lattices

   https://doi.org/10.1039/C9DT03389K  

   Smith Pellizzeri, Tiffany M. ; Sanjeewa, Liurukara D. ; Pellizzeri, Steven ; McMillen, Colin D. ; Garlea, V. Ovidiu ; Ye, Feng ; Sefat, Athena S. ; Kolis, Joseph W. ( April 2020 , Dalton Transactions)

   Two new alkali vanadate carbonates with divalent transition metals have been synthesized as large single crystals via a high-temperature (600 °C) hydrothermal technique. Compound I , Rb 2 Mn 3 (VO 4 ) 2 CO 3 , crystallizes in the trigonal crystal system in the space group P 3̄1 c , and compound II , K 2 Co 3 (VO 4 ) 2 CO 3 , crystallizes in the hexagonal space group P 6 3 / m . Both structures contain honeycomb layers and triangular lattices made from edge-sharing MO 6 octahedra and MO 5 trigonal bipyramids, respectively. The honeycomb and triangular layers are connected along the c -axis through tetrahedral [VO 4 ] groups. The MO 5 units are connected with each other by carbonate groups in the ab -plane by forming a triangular magnetic lattice. The difference in space groups between I and II was also investigated with Density Functional Theory (DFT) calculations. Single crystal magnetic characterization of I indicates three magnetic transitions at 77 K, 2.3 K, and 1.5 K. The corresponding magnetic structures for each magnetic transition of I were determined using single crystal neutron diffraction. At 77 K the compound orders in the MnO 6more »-honeycomb layer in a Néel-type antiferromagnetic orientation while the MnO 5 triangular lattice ordered below 2.3 K in a colinear ‘up–up–down’ fashion, followed by a planar ‘Y’ type magnetic structure. K 2 Co 3 (VO 4 ) 2 CO 3 ( II ) exhibits a canted antiferromagnetic ordering below T N = 8 K. The Curie–Weiss fit (200–350 K) gives a Curie–Weiss temperature of −42 K suggesting a dominant antiferromagnetic coupling in the Co 2+ magnetic sublattices.« less
5. Towards complex microarchitectural nanocomposites using non-uniform multi-field processing

   https://doi.org/10.1117/12.2515259  

   Al Masud, Md ; Erol, Anil ; Edson, Connor ; Ounaies, Zoubeida ; vonLockette, Paris ; Naguib, Hani E. ( March 2019 , Proc. SPIE 10968, Behavior and Mechanics of Multifunctional Materials XIII, 109680G)

   In this study, we investigated hierarchical microarchitecture formation of magnetic barium hexaferrite (BF) platelets inside the polydimethylsiloxane (PDMS) matrix using electric and magnetic field colloidal assembly technique. First, external fields were applied to the colloidal solution to form the microstructure before curing the composites. After microstructure formation the composites were cured to freeze the microstructure by the application of heat. We investigated two different cases in this study-(1) magnetic field processed composites and (2) multi-field processed composites which were processed under both magnetic and electric field. We observed that macro-chains formed due to the electric and magnetic field had much higher length compared to the macro-chains formed due to the just magnetic field. For both cases individuals BHF are found to be oriented in the direction of external field. The analysis of SEM microstructures using ImageJ and MATLAB showed that at least two different level of hierarchies are present in the microstructure for both cases which can be named as BHF stacks and micro-chains. From the microstructure analysis, we found that compared to just magnetic field processed composites, the orientation of individual particles, BHF stacks and micro-chains in relation to the external field were found to be higher for themore »multi-field processed composites. Magneto-electro-hydrodynamics modeling of the polymer-particulate mixture predicted similar behavior. Computational simulations were performed wherein particulates, subjected to both DEP forces and additional magnetic dipole interactions, were allowed to form quasi-equilibrium structures before locking in a final structure to represent curing. Results show that dielectrophoretic (DEP) force produced from the local non-uniform electric field facilitates the translation of the platelets towards formation of chain-like structure, while external magnetic field augmented the rotation of particles inside the chain-like structure. Analysis of the simulation of microstructures confirms that multiple level of hierarchies are present in the composites microstructure for both cases, while the case with both electric and magnetic fields produced longer chains. The understanding of the hierarchical microstructure formation using the multi-field processing technique will help in the future to fabricate more complex microarchitectures with resulting multi-material properties.« less