Unique properties of liquids and various processes in solutions originate from the solute-solute, solute-solvent, and solvent-solvent interactions in solutions. The structure and dynamics of liquids and solutions on the molecular level are thus essential for understanding the function and underlying mechanism of processes in solutions. Quantum beams, such as X-rays and neutrons, are of similar length and time scale as ions and molecules and are suited for this aim. Novel neutron scattering techniques for liquids and solutions have been developed for measurements over a wide range of concentration, temperature, and pressure. The techniques have been applied to various liquid systems, such as electrolyte solutions, supercritical fluids, confined and interfacial liquids, and solvent-induced denaturation of proteins.

The origin of multiferroics in the proper-screw magnetic structure, the superparamagnetism in relaxor ferroelectrics with the magnetic ions, and the magnetic anisotropy induced by the spin-nematic interaction were studied mainly by using the neutron scattering method by focusing on the relationship between the magnetism and the dielectricity. In these studies, a novel coupling between the magnetism and dielectricity, which is different from that in the typical multiferroics with the cycloidal magnetic structure, was discovered. Our new finding will open the door to a novel magnetoelectric effect.

We have investigated effects of uniaxial stress on frustrated magnets by means of neutron scattering experiment. In this article, we focus on a triangular lattice antiferromagnet CuFeO₂, which exhibits a strong spin-lattice coupling. We demonstrated uniaxial-stress control of electric polarization in a multiferroic phase of Ga-doped CuFeO₂. We also studied magnetic excitations in the collinear four-sublattice (4SL) antiferromagnetic ground state in undoped CuFeO₂ by means of inelastic neutron scattering measurements under uniaxial stress. We suggest that application of uniaxial-stress can be a useful tool to investigate geometrically frustrated spin systems, and can also induce novel cross-correlated phenomena in spin-lattice coupled systems.

Magnetic excitations in a polycrystalline sample of the metallic ferromagnet SrRuO₃ were observed by neutron Brillouin scattering, i.e., inelastic neutron scattering near the forward direction, on the High Resolution Chopper Spectrometer (HRC) installed at MLF J-PARC. While the observed spin wave dispersion is well described by the quadratic momentum dependence, the temperature dependence of the spin wave gap shows a nonmonotonous behavior, which can be related to that of the anomalous Hall conductivity. Weyl fermions that emerge at band crossings in momentum space caused by the spin-orbit interaction act as magnetic monopoles of the Berry curvature and contribute to a variety of novel transport phenomena such as anomalous Hall effect. The present result shows that the fictitious magnetic field produced by the Berry phase is an observable in inelastic neutron scattering and that the spin dynamics directly reflects the crucial role of Weyl fermions in the metallic ferromagnet.

We review the production of neutrons at the time of their discovery from the contemporary point of view. At that time, the nuclear reaction,⁴₂He (α-particle) + ⁹₄Be → ¹²₆C + n, was commonly used to obtain neutrons. The emitted radiation was initially considered to be γ-rays for the first time. However, it showed anomalous behavior and was sometimes called “beryllium radiation”. Using the neutron source and other, at the time, new equipment, the properties of the radiation were investigated by the pioneering researchers. There are a lot of things to learn from their ideas on the experimental apparatus and their attitude toward the research.