- Multiferroic and ferroelectric materials.

Mutriferroics are an interesting class of materials from viewpoints of application and basic physics. In multiferroics, two or all three of (anti)ferroelectricity, (anti)ferromagnetism, and ferroelasticity are observed in the same phase. We recently investigated ferroelectric, magnetic, and multiferroic properties of BiMO3 and PbMO3 prepared at high pressure of 6 GPa. Even in these simple systems we could find new compounds such as PbVO3, BiAlO3, BiGaO3, BiInO3, and 'BiVO3'. Some of them show promising ferroelectric properties. We could also clarify structural and magnetic properties of BiScO3, BiMnO3, and BiCrO3. In a very adaptive structural type of β-Ca3(PO4)2 that allows different substitution in all sublattices, ferroelectric and antiferroelectric properties were found depending on the cation compositions, e.g., Sr9Lu(VO4)7 and Ca9Fe(PO4)7 are ferroelectric and Sr9In(PO4)7 and Sr9NiLi(PO4)7 are antiferroelectric.

- Low-dimensional magnets.

One of the best-known so far one-dimensional Heisenberg S = 1/2 antiferromagnet was discovered, Sr2Cu(PO4)2. The importance of super-superexchange interactions in determination of magnetic lattice was demonstrated in a large number of compounds, e.g., MCuP2O7 (M = Ca, Sr, Ba, and Pb) and MCu2(PO4)2 (M = Sr and Pb). New spin-gap systems were found (MCu2(PO4)2 and Cu2PO4OH).