Quantifying nematic order in the evaporation-driven self-assembly of halloysite nanotubes: nematic islands and the critical aspect ratio.

Halloysite nanotubes (HNTs) are naturally occurring clay minerals found in the Earth's crust that typically exist in the form of high aspect-ratio nanometer-long rods. Here, we investigate the evaporation-driven self-assembly process of HNTs and show that a highly polydisperse collection of HNTs self-sort into a spatially inhomogeneous structure, displaying a systematic variation in the resulting nematic order. Through detailed quantification using the nematic order parameter S and nematic correlation functions, we show the existence of well-defined isotropic-nematic transitions in the emerging structures. We also show that the onset of these transitions gives rise to the formation of nematic islands, a phase resembling ordered nematic domains surrounded by an isotropic phase, which grow in size with S. Detailed image analysis indicates a strong correlation between local S and the local aspect ratio, L/D, with nematic order possible only for rods with L/D ≥ 6.5 ± 1. Finally, we conclude that the observed phenomena directly result from aspect ratio-based sorting in our system. Altogether, our results provide a unique method of tuning the local microscopic structure in self-assembled HNTs using L/D as an external parameter.

Exploring Magnetic XY Behavior in a Quasi-2D Anisotropic Triangular Lattice of Cu(II) by Functionalized Graphene.

Study on magnetism in two-dimensional (2D) spin-lattices is advancing rapidly. In this work, phase-pure botallackite (Bo) (Cu2(OH)3Br), a quasi-2D S = 1/2 anisotropic triangular spin-lattice is stabilized over 2D reduced graphene oxide (rGO) nanosheets via simple oxidation-reduction reaction chemistry. In comparison to polycrystalline Bo, such an anchoring resulted in the oriented growth of Bo crystallites in the Bo-rGO system. The Bo-rGO nanocomposite was found to be magnetically active with a Néel transition at ∼8.9 K, crossing over to possible XY anisotropy at ∼5 K-as revealed by complementary dc and ac susceptibility measurements-an unprecedented observation in the field assigned to an interfacial effect. This work demonstrates the potential usage of nonmagnetic 2D functionalized graphene to significantly modulate the magnetic properties of 2D spin-lattices.

Metamagnetism in Nanosheets of CoII-MOF with TN at 26 K and a Giant Hysteretic Effect at 5 K.

Herein, we have synthesized at room-temperature two-dimensional nanosheets of a MOF comprised of cobalt(II) ion with benzenedicarboxylic acid  ligand, which exhibited unusual magnetic properties. Direct-current magnetic susceptibility revealed an antiferromagnetic (AFM) transition at 26 K (Néel temperature,  TN) followed by a canting of the spin moments along with the concomitant appearance of a sigmoidal-shaped magnetization versus field ( M- H) curve at 15 K. Such a canted AFM ordering led to nonzero remnant magnetization with a remarkably high coercive field of ∼10 kOe at 5 K. Metamagnetism was further substantiated by the alternating-current magnetic susceptibility measurements.

Embedding S = 1/2 Kagome-like Lattice in Reduced Graphene Oxide.

An elegant platform to explore frustrated magnetism is the kagome spin lattice. In this work, clinoatacamite, a naturally occurring S = 1/2 kagome-like antiferromagnetic insulator, is synthesized in water at ambient pressure for the first time from a cuprous chloride (CuCl) precursor whereby Cu(I) was spontaneously oxidized to Cu(II) in the form of clinoatacamite [Cu2(OH)3Cl] with a simultaneous reduction of graphene oxide (GO) to reduced graphene oxide (rGO) in one pot. A stable nanocomposite of phase-pure clinoatacamite nanocrystals embedded in the rGO matrix was isolated. The clinoatacamite-rGO nanocomposite was determined to be magnetically active with a markedly enhanced coercive field of ∼2500 Oe at 5 K as well as electronically active with a conductivity value of ∼200 S·m-1 at 300 K. Our results illustrate an avenue of combining exotic magnetic and electronic lattices without impeding their individual characteristics and synergistically generating a new class of magnetic semiconductors.