I was awarded a prize by The Japanese Society for Neutron Science at 2009. The main topic of the title is the contribution to the structural science using neutron and x-ray. Special emphasis was adopted for the development of instrumentations. In this paper, the idea of structural science is given, and the importance of the crystal and magnetic structures for material properties will be discussed. Starting from my personal history for development of instrumentations on diffraction studies, I will touch the scientific results. At the last part, future development on this field will be overlooked.

Since the citation of this award is “neutron scattering research for low dimensional antiferromagnetism, metallic ferromagnetism as well as magnetic excitations in the superconducting oxides”, I mainly describe here that neutron scattering is devoted as the decisive tool for the research of ‘low dimensional magnetism’. Then I attach a brief story what I have been working on this subject in neutron scattering research field.

On the occasion of receiving Special Award from the Society, I would like to write my memories on the encounter of neutron science, together with expectation for this field.

Praseodymium-based compounds with a Pr³⁺ ion of 4f² configuration have effective magnetic moments of 3.6 μ_B/Pr at high temperature. However, the ground state is often non-magnetic when the Pr³⁺ ion has a nonmagnetic doublet ground state under a cubic crystal field. The twofold degeneracy is lifted by the ordering of the multipolar degrees of freedom. Such an example is PrPb₃, whose CEF ground state is the non-magnetic Γ₃ doublet. It was believed to involve an antiferroquadrupolar (AFQ) ordering at T_Q=0.4 K, where electric quadrupoles align alternatively. We have determined the order parameter and the quadrupole ordering structure in the AFQ phase by angle-resolved magnetization and neutron diffraction measurements; the quadrupole O₂⁰ is aligned with a sinusoidally modulated structure, whereas O₂² appears only at the fields higher than 6.5 T applied along the [110] direction. These suggest that the anisotropic interaction between the quadrupoles is an indirect RKKY-type interaction mediated by conduction electrons. Recently, superconductivity, structural transition and heavy fermion behavior have been observed in caged compounds PrT₂Zn₂₀ (T=Ru, Ir) with non-magnetic CEF ground states.

We review our recent studies on spin excitations by inelastic neutron scattering: (1) quasiparticle-like molecular spin excitation levels in geometrically frustrated magnet MgCr₂O₄ and (2) data conversion method of powder inelastic scattering data for one-dimensional systems.

A readout system employing high-speed network for using a linear position sensitive ³He gas detector (PSD) has been developed at KEK, and is widely used in experiments at the MLF of J-PARC.