In multiferroic CuFe0.95Al0.05O2, applying uniaxial pressure p generates a magnetoferroelectric phase distinct from the well-studied spin-driven ferroelectric phase associated with helical magnetic ordering in this system. Using a four-circle neutron diffractometer, the magnetic structure of the p-induced magnetoferroelectric phase is determined as the collinear sinusoidal type, which itself does not break the inversion symmetry in this system. Additionally, synchrotron radiation x-ray diffraction experiments are conducted to investigate how the triangular lattice in CuFe0.95Al0.05O2 is distorted by applied p. Although lattice distortion during the magnetic phase transition in CuFe0.95Al0.05O2 is mitigated by the substitution of nonmagnetic Al3+, the application of p along the conjugate direction revives the latent spin-lattice coupling, causing the triangular lattice to distort during magnetic phase transition. The application of a magnetic filed considerably reduces p-induced ferroelectric polarization, but does not affect lattice distortion. These results indicate that p-induced ferroelectric polarization is not a consequence of the piezoelectric effect. Instead, the sinusoidal magnetic structure would contribute to the emergence of p-induced ferroelectric polarization through spin-lattice coupling.

Recently, applying a uniaxial stress a of only 40 MPa along the a axis to a single domain structure of MnP has been found to modify the fractional coordinates of each ion irreversibly with respect to a, leading to the formation of crystal domains rotated by +/- 123.1 degrees around the b axis [Kozawa et al., Sci. Rep. 13, 13750 (2023)]. To reveal the process of this unusual domain formation, we measure the time evolution of magnetization due to the crystal domain formation and perform neutron diffraction measurements under a. Threshold stress causing domain formation increases as temperature (T ) decreases, and magnetization along the a axis (Ma) increases over time on the order of hours with a T-dependent relaxation time. These results suggest that this domain formation by a is thermally activated. Based on these results, we achieve controlling the crystal domain formation by regulating a and T. Moreover, although Ma increases on the order of hours, spatial disorder is not observed during the change in the fractional coordinates of each ion in the neutron diffraction measurement. This work paves the way for a crystal domain engineering method by using a, affecting both fundamental material science and the industrial utilization of materials.

NMR study has been performed on an S=1/2 antiferromagnet KCu _6 AlBiO _4 (SO _4 ) _5 Cl on the square-Kagomé lattice, which has three slightly inequivalent nearest-neighbor interactions. Because of the geometrical frustration inherited from triangles within the square kagomé lattice and of the low dimensionality, a long range magnetic order is strongly suppressed; its absence has so far been confirmed in low temperatures down to dilution refrigerator region. ^27 Al-NMR spectra and the longitudinal relaxation time T_1 were measured by a conventional pulsed spectrometer on powder sample under several magnetic fields between 3 and 10 T and in low temperatures down to 0.35 K. The NMR line width due to the inhomogeneous broadening increased with lowering temperatures and leveled off below 3 K, where FWHM reached the value as large as 0.1 T, implying that the ground state is magnetic one, consistent with previous reports. On the other hand, the longitudinal nuclear spin relaxation rate 1/T_1 obeyed the Arrhenius law with the thermal activation energy Δ = 2K at low temperatures, suggesting that a small gap is formed in the spin excitation spectrum.

In condensed matter physics, pressure is frequently used to modify the stability of both electronic states and atomic arrangements. Under isotropic pressure, the intermetallic compound MnP has recently attracted attention for the interplay between pressure-induced superconductivity and complicated magnetic order in the vicinity . By contrast, we use uniaxial stress, a directional type of pressure, to investigate the effect on the magnetism and crystal structure of this compound. An irreversible magnetisation response induced by uniaxial stress is discovered in MnP at uniaxial stress as low as 0.04 GPa . Neutron diffraction experiments reveal that uniaxial stress forms crystal domains that satisfy pseudo-rotational symmetry unique to the MnP-type structure. The structure of the coexisting domains accounts for the stress-induced magnetism. We term this first discovered phenomenon atomic reconstruction (AR) induced by uniaxial stress. Furthermore, our calculation results provide guidelines on the search for AR candidates. AR allows crystal domain engineering to control anisotropic properties of materials, including dielectricity, elasticity, electrical conduction, magnetism and superconductivity. A wide-ranging exploration of potential AR candidates would ensure that crystal domain engineering yields unconventional methods to design functional multi-domain materials for a wide variety of purposes.

$S=1/2$ Heisenberg ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ chain antiferromagnets have been investigated extensively due to their exotic magnetic states. Here, we report the magnetic behavior of birchite ${\mathrm{Cd}}_{2}{\mathrm{Cu}}_{2}{({\mathrm{PO}}_{4})}_{2}{\mathrm{SO}}_{4}\ifmmode\cdot\else\textperiodcentered\fi{}5{\mathrm{H}}_{2}\mathrm{O}$ and its effective spin model. Experimental studies by magnetic susceptibility, magnetization, heat capacity, and $\ensuremath{\mu}\mathrm{SR}$ measurements indicate the absence of long-range order down to 0.4 K. Theoretical studies reveal that birchite is a model compound for the ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ antiferromagnetic chain: the intrachain interactions ${J}_{1}$ and ${J}_{2}$ are antiferromagnetic and their magnitude is about 100 times larger than the interchain interactions. The magnitude of ${J}_{2}$ is two to three times larger than that of ${J}_{1}$, thus the spin gap is expected to be only a few percent of that of ${J}_{1}$. The temperature dependence of the specific heat shows a broad peak at about 1 K ($\ensuremath{\simeq}0.036{J}_{1}$), which suggests the presence of a spin gap.

S = 1/2 Heisenberg J(1)-J(2) chain antiferromagnets have been investigated extensively due to their exotic magnetic states. Here, we report the magnetic behavior of birchite Cd2Cu2(PO4)(2)SO4 center dot 5H(2)O and its effective spin model. Experimental studies by magnetic susceptibility, magnetization, heat capacity, and mu SR measurements indicate the absence of long-range order down to 0.4 K. Theoretical studies reveal that birchite is a model compound for the J(1)-J(2) antiferromagnetic chain: the intrachain interactions J(1) and J(2) are antiferromagnetic and their magnitude is about 100 times larger than the interchain interactions. The magnitude of J(2) is two to three times larger than that of J(1), thus the spin gap is expected to be only a few percent of that of J(1). The temperature dependence of the specific heat shows a broad peak at about 1 K (similar or equal to 0.036J(1)), which suggests the presence of a spin gap.

We report the magnetic structure and anisotropy of the quasi-one-dimensional $S=\frac{1}{2}$ antiferromagnet ${\mathrm{Na}}_{2}{\mathrm{CuSO}}_{4}{\mathrm{Cl}}_{2}$ obtained by single-crystal neutron scattering, electron spin resonance (ESR), and magnetization measurements, following an earlier study of its dynamics [M. Fujihala et al., Phys. Rev. B 101, 024410 (2020)]. A N\'eel-type spin structure is formed within the chain of this compound, where the spins point along the $b$ axis, and ESR data indicate an antisymmetric exchange with a uniform Dzyaloshinskii-Moriya (DM) vector pointing along the $b$ axis. The anisotropy $g$ factor and magnetic structure are strong indicators of magnetic anisotropy originating from a symmetric anisotropic exchange interaction and/or a magnetic dipole interaction. These results suggest that these terms of the anisotropic spin Hamiltonian counteract the effect of the DM interaction and stabilize the N\'eel-type structure in ${\mathrm{Na}}_{2}{\mathrm{CuSO}}_{4}{\mathrm{Cl}}_{2}$.

The $S=\frac{1}{2}$ quasi-one-dimensional antiferromagnet ${\mathrm{K}}_{2}{\mathrm{CuSO}}_{4}{X}_{2}\phantom{\rule{4pt}{0ex}}(X=\mathrm{Cl}$, Br) exhibits peculiar Dzyaloshinskii-Moriya (DM) interactions that are uniform along its spin chains and antiparallel with respect to neighboring chains. This feature has received much attention recently because it leads to spin frustration, however, the spin dynamics around ${T}_{\mathrm{N}}$ and magnetic structure have not been reported. Here we report magnetic behaviors of ${\mathrm{Na}}_{2}{\mathrm{CuSO}}_{4}{\mathrm{Cl}}_{2}$. The orthorhombic crystal structure of ${\mathrm{Na}}_{2}{\mathrm{CuSO}}_{4}{\mathrm{Cl}}_{2}$, which is identical to $\mathrm{K}{\phantom{\rule{0.16em}{0ex}}}_{2}{\mathrm{CuSO}}_{4}{X}_{2}$, was verified. The results of the thermodynamic measurements suggest that this compound has moderately strong intra- and interchain interaction for investigation of the spin state around ${T}_{\mathrm{N}}$. The inelastic neutron scattering and muon spin relaxation and rotation measurements reveal the presence of a two-spinon continuum, and below ${T}_{\mathrm{N}}$, the long-range order develops. However, the obtained critical exponent is $\ensuremath{\beta}=0.18$, which is not indicative of a three-dimensional magnetic system; instead, one-dimensional (1D) spin correlation likely affects the formation of magnetic ordering in ${\mathrm{Na}}_{2}{\mathrm{CuSO}}_{4}{\mathrm{Cl}}_{2}$. There is a possibility that ${\mathrm{Na}}_{2}{\mathrm{CuSO}}_{4}{\mathrm{Cl}}_{2}$ is a model compound for investigation of DM-induced frustration effects in a 1D quantum spin system.

Observation of a quantum spin liquid (QSL) state is one of the most important goals in condensed-matter physics, as well as the development of new spintronic devices that support next-generation industries. The QSL in two dimensional quantum spin systems is expected to be due to geometrical magnetic frustration, and thus a kagome-based lattice is the most probable playground for QSL. Here, we report the first experimental results of the QSL state on a square-kagome quantum antiferromagnet, KCu6AlBiO4(SO4)5Cl. Comprehensive experimental studies via magnetic susceptibility, magnetisation, heat capacity, muon spin relaxation (μSR), and inelastic neutron scattering (INS) measurements reveal the formation of a gapless QSL at very low temperatures close to the ground state. The QSL behavior cannot be explained fully by a frustrated Heisenberg model with nearest-neighbor exchange interactions, providing a theoretical challenge to unveil the nature of the QSL state.

K3Cu3AlO2(SO4)4 is a highly one-dimensional spin-1/2 inequilateral diamond-chain antiferromagnet. Spinon continuum and spin-singlet dimer excitations are observed in the inelastic neutron scattering spectra, which is in excellent agreement with a theoretical prediction: a dimer-monomer composite structure, where the dimer is caused by strong antiferromagnetic (AFM) coupling and the monomer forms an almost isolated quantum AFM chain controlling low-energy excitations. Moreover, muon spin rotation/relaxation spectroscopy shows no long-range ordering down to 90 mK, which is roughly three orders of magnitude lower than the exchange interaction of the quantum AFM chain. K3Cu3AlO2(SO4)4 is, thus, regarded as a compound that exhibits a Tomonaga-Luttinger spin liquid behavior at low temperatures close to the ground state.

Multiferroic orthorhombic o-LuMnO3 exhibits large ferroelectric polarization induced by an E-type magnetic order. Recently, the E-type magnetic phase in LuMnO3 was proposed to feature magnetic moments tilted away from the collinear ordering. We employed neutron diffraction to determine the symmetry of the magnetic order in o-LuMnO3. We observed that below T-N = 39 K, the Mn3+ spins order into an incommensurate amplitudemodulated phase that obeys the Pbnm crystal symmetry and is paraelectric. The incommensurate phase locks into a commensurate phase at T-C = 35.5 K described by a fully antiferromagnetic and noncollinear E-type order. This noncollinear E-type ordering breaks the spatial inversion symmetry and induces a spontaneous polarization at TC. At T = 2 K, an appreciably large electric polarization was observed similar to that of other orthorhombic manganites featuring E-type magnetic order. We also present a Pbnm symmetry-allowed Dzyaloshinskii-Moriya interaction that explains the noncollinear E-type order in the commensurate phase. These results are in qualitative agreement with the type of distortions from collinear E-type antiferromagnetic order found using Monte Carlo simulation for rare-earth manganites

Spin-1/2 compounds A(3)Cu(3)AlO(2)(SO4)(4) (A = K, Rb, and Cs) have one- dimensional (1D) inequilateral diamond chains. We analyze the temperature dependence of the magnetic susceptibility and determine the magnetic exchange interactions. In contrast to azurite, a dimer is formed on one of the sides of the diamond. From numerical analyses of the proposed model, we find that the dimer together with a nearly isolated 1D Heisenberg chain characterize magnetic properties including magnetization curve and magnetic excitations. This implies that a dimer-monomer composite chain without frustration is a good starting point for describing these compounds.

We have investigated magnetic and ferroelectric (dielectric) properties of multiferroic CuFe0.982Ga0.018O2, CuFe0.965Ga0.035O2, and CuFe0.95Al0.05O2 under applied uniaxial pressure p up to 600 MPa. Unlike the results of the almost same experiments on CuFeO2 [Tamatsukuri et al., Phys. Rev. B 94, 174402 (2016)], we have found that the application of p induces a new ferroelectric phase, which is different from the well-studied spin-driven ferroelectric phase with helical magnetic ordering, in all the doped samples investigated here. We have also constructed the temperature versus p magnetoelectric phase diagrams of the three samples. The ferroelectric polarization in the p-induced ferroelectric phase lies along the [110] direction as in the helical magnetoferroelectric phase, and its value is comparable with or larger than that in the helical magnetoferroelectric phase. The magnetic structure in the p-induced ferroelectric phase seems to be of a collinear sinusoidal type. Although this magnetic structure itself does not break the inversion symmetry, it is considered to play an important role in the origin of ferroelectricity in the p-induced ferroelectric phase through the spin-lattice coupling in this system.

K3Cu3AlO2(SO4)(4) is a highly one-dimensional spin-1/2 inequilateral diamond-chain antiferromagnet. Spinon continuum and spin-singlet dimer excitations are observed in the inelastic neutron scattering spectra, which is in excellent agreement with a theoretical prediction: a dimer-monomer composite structure, where the dimer is caused by strong antiferromagnetic (AFM) coupling and the monomer forms an almost isolated quantum AFM chain controlling low-energy excitations. Moreover, muon spin rotation/relaxation spectroscopy shows no long-range ordering down to 90 mK, which is roughly three orders of magnitude lower than the exchange interaction of the quantum AFM chain. K3Cu3AlO2(SO4)(4) is, thus, regarded as a compound that exhibits a Tomonaga-Luttinger spin liquid behavior at low temperatures close to the ground state.

We have investigated correlation between structural and electronic anisotropies in a parent compound of Fe-chalcogenide superconductor ${\mathrm{Fe}}_{1+\ensuremath{\delta}}\mathrm{Te}$ with $\ensuremath{\delta}=0.09$ by means of synchrotron x-ray diffraction and in situ in-plane resistivity anisotropy measurements with uniaxial stress applied along a tetragonal $a$ axis. This system is known to exhibit a tetragonal-to-monoclinic structural transition at ${T}_{\mathrm{S}}\ensuremath{\sim}60$ K. We have confirmed that the in-plane resistivity anisotropy in the low-temperature monoclinic phase is attributed to the asymmetry in volume fractions of the monoclinic domains, as was suggested in a previous study [Jiang et al., Phys. Rev. B 88 115130 (2013)]. On the other hand, we found another in-plane resistivity anisotropy above ${T}_{\mathrm{S}}$. The present x-ray diffraction and resistivity anisotropy measurements have revealed that this anisotropy is not due to an onset of the low-temperature monoclinic phase but to the lattice softening enhanced toward ${T}_{\mathrm{S}}$. As one of the possibilities, we suggest that the orbital fluctuation contributes to the lattice softening and the resistivity anisotropy above ${T}_{\mathrm{S}}$.

We have investigated correlation between structural and electronic anisotropies in a parent compound of Fe-chalcogenide superconductor Fe1+delta Te with delta = 0.09 by means of synchrotron x-ray diffraction and in situ in-plane resistivity anisotropy measurements with uniaxial stress applied along a tetragonal a axis. This system is known to exhibit a tetragonal-to-monoclinic structural transition at T-S similar to 60 K. We have confirmed that the in-plane resistivity anisotropy in the low-temperature monoclinic phase is attributed to the asymmetry in volume fractions of the monoclinic domains, as was suggested in a previous study [Jiang et al., Phys. Rev. B 88 115130 (2013)]. On the other hand, we found another in-plane resistivity anisotropy above T-S. The present x-ray diffraction and resistivity anisotropy measurements have revealed that this anisotropy is not due to an onset of the low-temperature monoclinic phase but to the lattice softening enhanced toward T-S. As one of the possibilities, we suggest that the orbital fluctuation contributes to the lattice softening and the resistivity anisotropy above T-S.

The new compound K3Cu3AlO2(SO4)(4), representing a spin 1/2 distorted diamond chain system, was synthesized and its magnetic properties were studied by magnetic susceptibility, specific heat, and high-field magnetization measurements. Magnetic Cu2+ ions were found to form a highly one-dimensional distorted diamond chain with strong intrachain interactions. Short-range magnetic correlations were observed to develop in a two-stage process without magnetic long-range ordering by magnetic susceptibility and specific heat measurements. The exchange constant ratio J(2)/J(1), where J(2) is the magnetic interaction of the diamond backbone and J(1) is the magnetic interaction of the monomers along the chain, was estimated to be 2.5, demonstrating that the magnetic ground state is composed of an alternating dimer -monomer spin-liquid phase. The absence of an M = 0 plateau in the high-field magnetization curve is also consistent with an alternating dimer-monomer model. These results strongly suggest that K3Cu3AlO2(SO4)(4) is the first material exhibiting an alternating dimer-monomer spin-liquid ground state.