- Activity Report 2015 -

Masuda Group

Magnetic Model in Multiferroic NdFe_{3}(BO_{3})_{4} Investigated by Inelastic Neutron Scattering

Fig. 1. Inelastic neutron scattering spectra obtained using HRC, along the (a) *c** and (b) *a** directions. The curves are the calculated spin-wave dispersions.

Symmetry breaking of time reversal and space inversion allows spontaneous order both in magnetism and dielectricity. The enhanced simultaneous order, multiferroics [1], has been extensively studied since the discovery of its experimental realization in the perovskite manganite TbMnO_{3} [2]. The microscopic consideration of electronic states taking into account a spin-orbit interaction and symmetry of crystals reveals the relationship between the structures of spin and polarization. So far, in many multiferroic materials, the complex spin structure of the 3*d* transition metal ions has been focused in relation with induced electric polarizations. On the other hand, existence of an interaction between 4*f* and 3*d* ions (*f*-*d* coupling) and its importance on the multiferroic structure has not been in the spotlight. In this context, an easy-plane type antiferromagnet NdFe_{3}(^{11}BO_{3})_{4} provides a simple and interesting playground in which Nd and Fe moments are simultaneously ordered thorough the *f*-*d* coupling and the polarizations are simply described by a rank two tensor of local magnetic operators. Recently we performed inelastic neutron scattering (INS) measurements on single crystals of hexagonal 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 and its relation to the multiferroic structure by using state-of-the-art neutron spectrometer HRC [3].

The INS spectra projected onto *ħω-c** and *ħω* -*a** plane are shown in Figs. 1(a) and 1(b). We clearly observed the spin waves of the Fe^{3+} moments around AF zone center at ** q** = (0,0, −1.5), and the flat excitation at about 1.0 meV from the crystal field of Nd

**References**

- [1] W. Eerenstein, N. D. Mathur, and J. F. Scott, Nature (London)
**442**, 759 (2006). - [2] T. Kimura, T. Goto, H. Shintani, K. Ishizaka, T. Arima, and Y. Tokura, Nature
**426**, 55 (2003). - [3] S. Hayashida, M. Soda, S. Itoh, T. Yokoo, K. Ohgushi, D. Kawana, H. M. Ronnow, and T. Masuda, Phys. Rev. B
**92**, 054402 (2015).

**Authers**

- S. Hayashida, M. Soda, S. Itoh, T. Yokoo, K. Ohgushi, D. Kawana, H. M. Ronnow, and T. Masuda