Investigation of the Magnetic Model in Multiferroic NdFe$_{3}$(BO$_{3}$)$_{4}$ by Inelastic Neutron Scattering

We performed inelastic neutron scattering measurements on single crystals of NdFe$_{3}$($^{11}$BO$_{3}$)$_{4}$ to explore the magnetic excitations, to establish the underlying Hamiltonian, and to reveal the detailed nature of hybridization between the 4$f$ and 3$d$ magnetism. The observed spectra exhibiting a couple of key features, i.e., anti-crossing of Nd- and Fe-excitations and anisotropy gap at the antiferromagnetic zone center, are explained by the magnetic model including spin interaction in the framework of weakly-coupled Fe$^{3+}$ chains, interaction between the Fe$^{3+}$ and Nd$^{3+}$ moments, and single-ion anisotropy derived from Nd$^{3+}$ crystal field. The combination of the measurements and calculations reveals that the hybridization between 4$f$ and 3$d$ magnetism propagates the local magnetic anisotropy of the Nd$^{3+}$ ion to the Fe$^{3+}$ network, resulting in the bulk structure of multiferroics.

Spin Model of O2-based Magnet in a Nanoporous Metal Complex

Inelastic neutron scattering experiments are performed on a nanoporous metal complex Cu-Trans-1,4-Cyclohexanedicarboxylic Acid (Cu-CHD) adsorbing O2 molecules to identify the spin model of the O2-based magnet realized in the host complex. It is found that the magnetic excitations of Cu-CHDs adsorbing low- and high-concentration O2 molecules are explained by different spin models, the former by spin dimers and the latter by spin trimers. By using the obtained parameters and also by assuming that the levels of the higher energy states are reduced because of the non-negligible spin dependence of the molecular potential of oxygen, the magnetization curves are explained in quantitative level.

Experimental confirmation of spin gap in antiferromagnetic alternating spin-3/2 chain substances RCrGeO5 (R = Y or 154Sm) by inelastic neutron scattering experiments

A spin-singlet ground state with a spin gap has been discovered in antiferromagnetic spin chain substances when the spin value is 1/2, 1 or 2. To find spin gap (singlet-triplet) excitations in spin-3/2 chain substances, we performed inelastic neutron scattering and magnetization measurements on {it R}CrGeO$_5$ ({it R} = Y or Sm) powders. As expected, we observed spin gap excitations and the dispersion relation of the lowest magnetic excitations. We proved that the spin system of Cr$^{3+}$ was an antiferromagnetic alternating spin-3/2 chain.

Spin nematic interaction in multiferroic compound Ba$_{2}$CoGe$_{2}$O$_{7}$

We demonstrate the existence of the spin nematic interactions in an easy-plane type antiferromagnet Ba$_{2}$CoGe$_{2}$O$_{7}$ by exploring the magnetic anisotropy and spin dynamics. Combination of neutron scattering and magnetic susceptibility measurements reveals that the origin of the in-plane anisotropy is an antiferro-type interaction of the spin nematic operator. The relation between the nematic operator and the electric polarization in the ligand symmetry of this compound is presented. The introduction of the spin nematic interaction is useful to understand the physics of spin and electric dipole in multiferroic compounds.