Spin dynamics in natural multiferroic pyroxene NaFeSiO

天然マルチフェロイイック輝石NaFeSiOのスピンダイナミクス

Prokhnenko, O.*; Nikitin, S. E.*; 金子 耕士   ; 田端 千紘; 廣瀬 雄介; 常盤 欣文  ; 芳賀 芳範   ; 藤田 全基; 野尻 浩之*; Anovitz, L. M.*; Podlesnyak, A.*

Prokhnenko, O.*; Nikitin, S. E.*; Kaneko, Koji; Tabata, Chihiro; Hirose, Yusuke; Tokiwa, Yoshifumi; Haga, Yoshinori; Fujita, Masaki; Nojiri, Hiroyuki*; Anovitz, L. M.*; Podlesnyak, A.*

The spin dynamics in the natural mineral aegirine, NaFeSiO, a member of the pyroxene family, was studied using elastic and inelastic neutron scattering. Magnetization and specific heat measurements as well as single-crystal neutron diffraction maps confirm two successive magnetic transitions at 8.8 and 5.8~K, consistent with previous studies. The observed spin-wave excitations emerge from the incommensurate magnetic Bragg peaks corresponding to the propagation vector , and extend up to energies of about 1.5 meV. In the low-temperature helical phase, the spin dynamics of the Fe ions is well described by a simple linear spin-wave model. The observed excitations can be modeled using a spin Hamiltonian that includes three primary exchange interactions. Our results show that no single exchange interaction dominates the spin dynamics. The similar strengths of the intrachain and interchain couplings point to the fact that the magnetic interactions in aegirine are three-dimensional, rather than being confined along one direction. As a result, the system cannot be considered quasi-one-dimensional, as previously suggested, and calls for further investigations.