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 th
e 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.
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.
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 measur
ements 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.
We study field induced quantum phase in weakly-coupled ferromagnetic frustrated chain LiCuVO$_4$ by neutron diffraction technique. A new incommensurate magnetic peak is observed at $H ge 8.5$ T. The field dependent propagation vector is identified wi
th the spin density wave correlation in the theoretically predicted magnetic quadrupole order. Quantum fluctuation, geometrical frustration, and interchain interaction induce the exotic spin density wave long-range order in the insulating magnet.
Spin dynamics of the square lattice Heisenberg antiferromagnet, BaMnGeO, is studied by a combination of bulk measurements, neutron diffraction, and inelastic neutron scattering techniques. Easy plane type antiferromagnetic order is identified at $T l
e 4.0$ K. The exchange interactions are estimated as $J_1$ = 27.8(3)${mu}$eV and $J_2$ = 1.0(1) ${mu}$eV, and the saturation field $H_{rm C}$ is 9.75 T. Magnetic excitation measurements with high experimental resolution setup by triple axis neutron spectrometer reveals the instability of one magnon excitation in the field range of $0.7H_{rm C} lesssim H lesssim 0.85H_{rm C}$.
We study $S=1/2$ dimer excitation in a coupled chain and dimer compound Cu$_2$Fe$_2$Ge$_4$O$_{13} by inelastic neutron scattering technique. The Zeeman split of the dimer triplet by a staggered field is observed at low temperature. With the increase
of temperature the effect of random field is detected by a drastic broadening of the triplet excitation. Basic dynamics of dimer in the staggered and random fields are experimentally identified in Cu$_2$Fe$_2$Ge$_4$O$_{13}.
We performed inelastic neutron scattering experiment to study magnetic excitation of O$_2$ molecules adsorbed in microporous compound. The dispersionless excitation with characteristic intensity modulation is observed at $hbar omega = 7.8$ meV at low
temperature. The neutron cross section is explained by spin dimer model with intradimer distance of 3.1 AA . Anomalous behaviour in the temperature dependence is discussed in the context of enhanced magnetoelasticity in the soft framework of O$_2$ molecule.
Cu$_2$Fe$_2$Ge$_4$O$_{13}$ is a bicomponent compound that consists of Cu dimers and Fe chains with separate energy scale. By inelastic neutron scattering technique with high-energy resolution we observed the indirect Fe - Fe exchange coupling by way
of the Cu dimers. The obtained parameters of the effective indirect interaction and related superexchange interactions are consistent with those estimated semi-statically. The consistency reveals that the Cu dimers play the role of nonmagnetic media in the indirect magnetic interaction.
