Elastic neutron scattering experiments showed incommensurate antiferromagnetic peaks in 5% Fe-substituted Bi-2201 cuprate in the non-superconducting heavily overdoped regime. The incommensurability S similar to 0.21 is comparable to that observed in Fe-substituted Bi-2201 in the overdoped regime. [Hiraka et al., Phys. Rev. B 81, 144501 (2010).] The magnetic correlation length is comparable between the overdoped and non-superconducting heavily overdoped regimes. It is plausible that incommensurate antiferromagnetic order is induced and stabilized by Fe in the heavily overdoped regime, which suggests a robust antiferromagnetic correlation beyond the superconducting dome in the phase diagram.

The ternary transition-metal oxide Fe2Mo3O8 is a polar magnet characterized by a layered structure of magnetic Fe honeycomb lattices and non-magnetic Mo kagome lattices. Whereas previous studies have primarily focused on the chemical substitution at the Fe sites to modulate the magnetic properties, the Mo sites have remained largely unexplored due to the strong spin-singlet trimerization of Mo4+ ions. In this study, we investigated the effect of substituting non-magnetic Pb4+ and Zr4+ ions into the Mo sites to intentionally disrupt the Mo trimers. Our results reveal that the disruption of the Mo spin-singlet state induces active spins within the Mo layer, resulting in the emergence of a ferromagnetic-like behavior that persists even at room temperature. Quantitative analysis that takes into account the weight fraction of the main phase suggests an effective spin S = 1/2 state per active Mo ion upon trimer disruption. These findings demonstrate that controlling non-magnetic cluster states within a polar host via chemical substitution is a promising approach for designing room-temperature magnetoelectric materials.

We report on the single-crystal growth and magnetoelectric properties of the polar cluster magnets $\text{Ba}_{6} \text{Ln}_{2} \text{Fe}_{4} \mathrm{O}_{15}$ ($\text{Ln}=\text{La}$, Pr, Nd). These single crystals enable us to clarify the intrinsic magnetic anisotropy and magnetoelectric response of this polar cluster system, which remained elusive in previous polycrystalline studies [1]. Magnetization measurements reveal that the magnetic anisotropy strongly depends on the $L n$ ion; the $P r$ system exhibits Ising-like anisotropy, while the $N d$ and La systems behave as Heisenberg-like magnets. Additionally, in $\text{Ba}_{6} \text{La}_{2} \text{Fe}_{4} \mathrm{O}_{15}$, we discovered a significant magnetic-field-induced change in spontaneous electric polarization. This electric polarization change emerges continuously with the magnetic phase transition from the cluster-antiferromagnetic to the cluster-ferromagnetic phase. These findings demonstrate a sizeable magnetoelectric effect in a magnetic cluster system whose spin structure can be readily tuned by an external magnetic field.

We have investigated the electronic structure of LaSr2Mn2O7 in the CE-type antiferromagnetic (CE-AFM) state below the N & eacute;el temperature using micro-focused angle-resolved photoemission spectroscopy (mu-ARPES) and tight-binding models. In agreement with the tight-binding calculations, we found a dispersive intensity around the X point in the mu ARPES spectra, where the A-type antiferromagnetic (A-AFM) phase has no bands experimentally and theoretically, demonstrating that we have successfully captured the signatures of the CE-AFM band structure for the first time. Many observed features can be explained by the CE-AFM tight-binding bands, although some of them and the overall nearFermi level intensity mapping can be explained by the A-AFM band structure. This indicates that the CE-AFM domain size would be no larger than the beam footprint size of a similar to 20 & micro;m scale.

Fe2Mo3O8, known as the mineral kamiokite, is a layered compound consisting of Fe-honeycomb and Mo-kagome layers. The $\text{Mo}^{4+}$ ions form non-magnetic trimeric units through spin singlet formation, while the Fe layer exhibits antiferromagnetic ordering below 60 K. We investigated the effect of Mo-site substitution by $\mathbf{P b}^{4+}$ ions $(\mathbf{5} d^{10})$ and $\mathbf{Z r}^{4+}$ ions $(\mathbf{4} d^{0})$ as references, which share the same formal valence but differ in ionic size and electronic structure. Our findings reveal a systematic enhancement and thermal robustness of the magnetization, suggesting partial disruption of the non-magnetic Mo trimer configuration and the emergence of a weak ferromagnetic state that persists at least up to 350 K.

We investigated the Cu-spin correlation in the overdoped regime of the electron-doped high-Tc cuprate thin films of La2-xCexCuO4, changing the reduction condition from muon spin relaxation using low-energy muons. The Cu-spin correlation developed at low temperatures for optimally reduced films with x = 0.13 as well as x = 0.17 where the superconductivity was almost suppressed. These results are contrary to those observed in the hole-doped high-Tc cuprates where the development of the antiferromagnetic Cu-spin correlation disappears together with the suppression of superconductivity. The Cu-spin correlation developed at low temperatures in x = 0.17 may be understood in terms of antiferromagnetism, but it may be related to a ferromagnetic order recently suggested in the nonsuperconducting heavily overdoped La2-xCexCuO4 with x similar to 0.18.

This study investigates the dependence of the static magnetoelectric (ME) effect on the external field direction in the pyroelectric-ferrimagnet CaBaCo_4O_7, a topic that remains largely unexplored compared to dynamical nonreciprocal ME effects. We measured the magnetization with respect to the inherent polarization and found that an external electric field stabilizes the ferrimagnetic phase when applied parallel to the polarization, and destabilizes it when antiparallel. These results clearly demonstrate the electric-field-direction dependent control of the static ME effect, suggesting a new route to enhancing ME effects in pyroelectric-magnetic materials.

We performed high-magnetic-field magnetization, polarization, and ultrasonic measurements in Ba$_2$CuGe$_2$O$_7$ to investigate field-induced multiferroic properties arising from a cross-correlation between electric dipoles and electric quadrupoles in addition to cross-correlation between magnetic dipoles and electric dipoles. Magnetization $M$ shows saturation behavior above 20 T for several magnetic field directions, however, electric polarization $P_c$ exhibits an increase, and elastic constants show a softening above 20 T. Based on quantum states with a crystalline electric field for the $D_{2d}$ point group and $d$-$p$ hybridization between Cu-$3d$ and O-$2p$ electrons, we confirmed that the matrix of an electric dipole $P_z$ was proportional to that of an electric quadrupole $O_{xy}$. Furthermore, considering the spin-orbit coupling of $3d$ electrons and the Zeeman effect, we showed that $P_z$ and $O_{xy}$ simultaneously exhibited field-induced responses. These findings indicate that the orbital degrees of freedom, in addition to the spin degrees of freedom, contribute to the high-field multiferroicity in Ba$_2$CuGe$_2$O$_7$.

We have grown single crystals of mixed -valence pseudobrookite titanate MgTi 2 O 5 -Ti 3 O 5 systems (Mg 1 - x Ti 2 + x O 5 ) and have systematically investigated their physical properties as a novel canonical mixedvalence system which shows a successive change from the nonmagnetic band insulating phase (MgTi 2 O 5 ) to the charge -ordered spin -singlet dimer phase (Ti 3 O 5 ). In comparison with Al 1 - x Ti 2 + x O 5 [R. Takahama et al. , Phys. Rev. Mater. 4 , 074401 (2020)], we have clarified that, in the lower x region of Mg 1 - x Ti 2 + x O 5 , the physical properties are greatly affected by the change of electron density with a variation of x and we have found that the doped electrons enhance the optical conductivity along a Ti -Ti ladder direction. However, we have also clarified that, in the higher x region, almost all Ti 3 + ions produced by an increase in x contribute not to an increase in itinerant electrons but to a development of Ti 3 + -Ti 3 + dimer correlation. These observations indicate a crossover from the conductance along the ladder direction to a nontrivial conductance under the background of the dimer correlation.

The titanium dioxide (TiO2; anatase as main phase) nanoparticles were prepared by the homogenous precipitation, using ammonium titanium oxalate ((NH4)2TiO(C2O4)2·H2O) and urea (CO(NH2)2) as precipitant, followed by the heat treatment in air. The preparation of the fibrous octacalcium phosphate (Ca8(HPO4)2(PO4)4·5H2O: OCP) was also conducted by homoge-neous precipitation. The homogeneous mixing of TiO2 nanoparticles with fibrous OCP was conducted by suction filtration, and the hybridized sheet was obtained by the heat treatment in air. Although OCP was thermally decomposed to form hy-droxyapatite (Ca10(PO4)6(OH)2) and γ-calcium diphosphate (γ-Ca2P2O7), the fibrous morphology remained unchanged. The TiO2 nanoparticles were homogeneously dispersed on the surface of fibrous OCP. The excellent photocatalytic performance of the hybridized sheet was confirmed by the rapid degradation of the methylene-blue solution. Overall, TiO2-OCP hybridized sheets were found to possess potential utilization in the field of environmental remediation and wastewater treatment.

Single crystals of Ba3-xYbxTa5O15 with a tetragonal tungsten bronze structure were grown using a floating-zone technique, and their transport and magnetic properties, optical spectra, and specific heat were measured. It was found that this series of compounds exhibits a valence change of Yb ions from 2+ to 3+ with increasing x. This can be explained by assuming that the Yb2+ level exists immediately below the Fermi level in Ta 5d states, which decreases in energy with increasing x. It was also found that a positive magnetoresistance up to 3 T and a negative magnetoresistance above 3 T appear at low temperatures for x >= 1.0, indicating a peculiar state of Yb in this series of compounds.

(Received 5 March 2024; accepted 23 April 2024; published 7 May 2024) Barium tantalate with a tetragonal tungsten bronze structure, Ba 3 Ta 5 O 15 , and compounds where Ba is partly substituted by various rare earths ( R ), Ba 3 - x R x Ta 5 O 15 , were synthesized as single crystals, and their transport, magnetic, and magnetotransport properties were investigated. It was found that the compounds with Eu substitution show a relatively large negative magnetoresistance arising from the interaction between the conduction electrons in the Ta 5 d orbital and the localized spins in the Eu 4 f orbital.

We performed high-magnetic-field magnetization, polarization, and ultrasonic measurements in ${\mathrm{Ba}}_{2}{\mathrm{CuGe}}_{2}{\mathrm{O}}_{7}$ to investigate field-induced multiferroic properties arising from a cross-correlation between electric dipoles and electric quadrupoles in addition to cross-correlation between magnetic dipoles and electric dipoles. Magnetization $M$ shows saturation behavior above 20 T for several magnetic field directions, however, electric polarization ${P}_{c}$ exhibits an increase, and elastic constants show a softening above 20 T. Based on quantum states with a crystalline electric field for the ${D}_{2d}$ point group and $d\text{\ensuremath{-}}p$ hybridization between Cu-$3d$ and O-$2p$ electrons, we confirmed that the matrix of an electric dipole ${P}_{z}$ was proportional to that of an electric quadrupole ${O}_{xy}$. Furthermore, considering the spin-orbit coupling of $3d$ electrons and the Zeeman effect, we showed that ${P}_{z}$ and ${O}_{xy}$ simultaneously exhibited field-induced responses. These findings indicate that the orbital degrees of freedom, in addition to the spin degrees of freedom, contribute to the high-field multiferroicity in ${\mathrm{Ba}}_{2}{\mathrm{CuGe}}_{2}{\mathrm{O}}_{7}$.

Preparation conditions of titanium oxide (TiO 2 ) powders were examined by the hydrolysis of titanium potassium oxalate (K 2 TiO(C 2 O 4 ) 2 ), through the homogeneous precipitation method (80oC for 24 h) and hydrothermal treatment (160 or 170oC for 1 h). According to the Rietveld analysis, almost a single phase of anatase TiO 2 could be obtained by the hydrothermal treatment at 160oC for 1 h, followed by the heating at 900oC for 10 min in air. The molar ratio of anatase to rutile TiO 2 was found to be controlled by optimizing the hydrothermal conditions in the solution and the heating conditions in air for the photocatalytic activity.

We studied barium niobates with a tetragonal tungsten bronze structure in which Ba is substituted by various rare earths including divalent Eu and trivalent La, Ce, Pr, Nd, and Sm. The magnitude of the negative magnetoresistance observed for Ba3-xEuxNb5O15 increases near the metal-insulator phase boundary of a series of compounds at x similar to 2.2, where the number of carriers estimated using the Hall coefficient decreases by two orders of magnitude from that of the parent compound. Various transport properties, specific heat, and the optical reflectivity spectra of the series of compounds were measured and it was found that all the results can be explained by the changes in the number of carriers n and the effective mass m*, except for the anomalous decrease in the Seebeck coefficient from x = 0 to 1.