Spin dynamics in natural multiferroic pyroxene NaFeSiO

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, which exhibits multiferroic properties, was studied using elastic and inelastic neutron scattering. Magnetism in pyroxenes arises from competing intra- and interchain exchanges that stabilize a variety of commensurate and incommensurate states. The incommensurate helical ground state remains robust, with no metamagnetic transitions observed and only gradual spectral changes under field. A phase diagram constructed in terms of the exchange ratios and captures the transition between commensurate and incommensurate regimes and unifies magnetic behavior across different pyroxenes. Despite structural variations ( vs ), the exchange topology and resulting magnetic frustration are closely related. These results establish NaFeSiO as a benchmark for understanding exchange-driven magnetism and field-stable spin dynamics in pyroxenes with three-dimensional magnetic coupling.