Yukio Noda

The microscopic origin of the low-field 1/9 magnetization plateau in spin-1/2 kagome antiferromagnets remains unresolved. Here we show that chemical pressure reshapes the hierarchy of fractional plateaus in the titanium-based kagome family Cs8AB3Ti12F48 (A = Rb, Li; B = K, Na). High-field measurements up to 60 T reveal a robust 1/9 plateau-like phase in the expanded Cs8RbK3Ti12F48 and Cs8LiK3Ti12F48 compounds, despite the absence of the conventionally more robust 1/3 plateau. In contrast, compressed Cs8LiNa3Ti12F48 exhibits neither the 1/9 plateau-like phase nor a quantum-disordered ground state. Specific heat measurements and first-principles calculations show that lattice expansion preserves a frustrated, fully connected kagome exchange network and gapless quantum-disordered ground states, whereas compression reorganizes the network into weakly coupled quasi-one-dimensional subsystems and induces successive magnetic transitions. These results demonstrate that the 1/9 and 1/3 plateaus need not share a common microscopic origin and suggest that the 1/9 plateau may be a more universal feature of frustrated spin-1/2 kagome magnetism.

We demonstrate that a multi-k incommensurate magnetic state in the Weyl semimetal CeAlGe gives rise to a singular angular magnetoresistance (SAMR), which is an electrical transport signature capable of detecting magnetic field direction with exceptional precision. In contrast, its sister compound CeAlSi is devoid of both multi-k order and SAMR. We reveal that both phenomena appear upon 57% Ge substitution in CeAlSi_{1-x}Ge_{x} and coincide with electronic structure changes that soften the single-ion in-plane anisotropy and enhance Weyl-mediated magnetic interactions. These results unveil a remarkable connection between band topology, electronic transport, and collective magnetism in Weyl semimetals.

How particular bonds form in quantum materials has been a long-standing puzzle. Two key concepts dealing with charge degrees of freedom are dimerization (forming metal-metal bonds) and charge ordering. Since the 1930s, these two concepts have been frequently invoked to explain numerous exciting quantum materials, typically insulators. Here we report dimerization and charge ordering within the dimers coexisting in metallic NaRu₂O₄. By combining high-resolution x-ray diffraction studies and theoretical calculations, we demonstrate that this unique phenomenon occurs through a new type of bonding, which we call Z-type ordering. The low-temperature superstructure has strong dimerization in legs of zigzag ladders, with short dimers in legs connected by short zigzag bonds, forming Z-shape clusters: simultaneously, site-centered charge ordering also appears. Our results demonstrate the yet unknown flexibility of quantum materials with the intricate interplay among orbital, charge, and lattice degrees of freedom.

Solid solutions of (1- x )BiFeO 3 – x BaTiO 3 ( x = 0.0–1.0) were studied by the combination of X-ray and neutron powder diffraction methods in order to investigate structural and magnetic properties over a wide temperature region. The structure analyses revealed that there exists a hexagonal phase over the wide range of x , and a coexistence of a cubic or a tetragonal phase was revealed. The compositions of the two coexisting phases differ from each other, and Ba and Ti were found to favor the cubic or tetragonal phase. As x increases, the relaxation of the rhombohedral distortion in the hexagonal phase was observed. The decreases of the ferroelectric and the antiferromagnetic phase transition temperatures were also observed leading the suppression of the polarization and the magnetic moment of Fe 3+ ion at room temperature. As a whole, the ferroelectricity and ferromagnetism in this material were considered to arise from the remaining hexagonal phase.