Identification of microscopic spin-polarization coupling in the ferroelectric phase of magnetoelectric multiferroic CuFeAlO

Nakajima, Taro*; Mitsuda, Setsuo*; Inami, Toshiya; Terada, Noriki*; Osumi, Hiroyuki*; Prokes, K.*; Podlesnyak, A.*

We have performed synchrotron X-ray and neutron diffraction measurements on magnetoelectric multiferroic CuFeAlO (x=0.0155), which has a proper helical magnetic structure with incommensurate propagation wave vector in the ferroelectric phase. The present measurements revealed that the ferroelectric phase is accompanied by lattice modulation with a wave number 2, where is the magnetic modulation wave number. We have calculated the Fourier spectrum of the spatial modulations in the local electric polarization using a microscopic model proposed by T. Arima. Comparing the experimental results with the calculation results, we found that the origin of the 2-lattice modulation is the variation in the metal-ligand hybridization between the Fe ions and O ions. Combining the present results with the results of a previous polarized neutron diffraction study, we conclude that the microscopic origin of the ferroelectricity in CuFeAlO is the variation in the metal-ligand hybridization with spin-orbit coupling.