Two types of interesting physics in 4f-electron systems studied by neutron scattering techniques are reviewed: (i) One-dimensional quantum magnetism in Yb₄As₃, (ii) Formation of magnetic polaron lattice in the low carrier system Ce-monopnictides．

Effects of hydration on dynamics of Staphylococcal nuclease were examined by inelastic neutron scattering. At cryogenic temperatures, hydration affected the collective motions with energies lower than 5 meV, whereas the high-energy localized motions were independent of hydration. The frequency-upshift of the boson peak was also observed with hydration. These results suggest hardening of harmonic potential at local minima on the energy landscape. The 240 K transition was observed only for the hydrated protein, but not for the partially hydrated protein. On the other hand, partial hydration is sufficient to affect the harmonic nature of protein dynamics. The interesting and important finding is that there is a threshold hydration level to activate the anharmonic motions. Thus, hydration water controls both the harmonic and anharmonic protein dynamics by different mechanisms.

Current topics of relaxor studies are summarized with focusing on the quantum relaxor KTaO₃ doped with Li, which bears all the characteristics of the prototype relaxor; (1) dielectric response described by the Vogel-Fulcher law, (2) history dependence of the order parameter, (3) slow development of the order parameter after an extremely long incubation time, and (4) nucleation and growth of the polar nano-region in non-polar matrix. In addition, the tri-critical point that separates the first and second order phase transitions is located in the vicinity of the line of critical end points, which enhances the dielectric response of the system. This kind of critical behavior is originated from the complex competition between a long-range Coulomb interaction, a short-range dipolar interaction, a quantum fluctuation (zero-point vibration) and a random field. This phenomenon is promising for the future trend of functional material quests.

Since neutron reflectometry has a superior depth resolution in a few Å scale, it is suitable for a precise investigation of a polymer/polymer interface. If time evolution of an interfacial thickness can be evaluated by neutron reflectivity measurements, it is possible to clarify mobility or dynamics at a polymer/polymer interface. In this article, we explain the interdiffusion of polystyrene/deuterated polystyrene bilayer films as a typical example of diffusion phenomenon of polymer chains examined by neutron reflectivity. We also describe sample preparation and data analyses for beginners.

As stated in the previous review by Kawaguchi and Matsushita, neutron reflectometry (NR) enables us to gain direct access to density or composition profile along the direction normal to the surface with an excellent depth resolution being better than 1 nm. We here show our recent results dealing with density profiles of a perdeuterated poly(methyl methacrylate) (dPMMA) film spin-coated on a substrate in water, hexane and methanol, which are typical “non-solvents” for dPMMA. The interfaces of dPMMA with the liquids were diffuse in comparison with the pristine interface with air; the interfacial width with water was thicker than that with hexane. Interestingly, in water, the dPMMA film was composed of a swollen layer and the interior region, which also contained water, in addition to the diffused layer. The interface of dPMMA with hexane was sharper than that with water. Although there were slight indications of a swollen layer for the dPMMA in hexane, the solvent molecules did not penetrate significantly into the film. On the other hand, in methanol, the whole region of the dPMMA film was strikingly swollen. The modulus of dPMMA in the vicinity of the interfaces with liquids was also examined on the basis of force-distance curves measured by atomic force microscopy (AFM). The modulus decreased closer to the outermost region of the film. The extent to which the modulus decreased in the interfacial region was consistent with the amount of liquid sorbed into the film.