Spin-helicity-dependent magnetic domain growth in a spin-driven multiferroic under applied electric field

The effects of poling electric field on sizes of magnetic domains have been investigated for a spin-driven multiferroic ${\text{CuFe}}_{1-x}{\text{Al}}_x{\text{O}}_2$, whose ferroelectricity is driven by a screw-type magnetic ordering. By means of polarized neutron-diffraction measurements, we have demonstrated that the application of the electric field on cooling results in differences not only in volume fraction between the right-handed- and the left-handed-helical magnetic domains but also in average size between them. This indicates that on the ferroelectric transition, the electric field accelerates growth of the magnetic domains having ferroelectric polarization parallel to the electric field and suppresses the other.

Figure 1

(Color online) (a) Crystal structure of CFO with a hexagonal basis. (b) The screw-type magnetic structure in the FE-ICM phase. (c) Schematic drawing of the arrangements of the six types of multiferroic domains in the FE-ICM phase. Open and filled arrows denote the directions of the ferroelectric polarization induced by the RH- and the LH-helical magnetic domains.

Figure 2

(Color online) (a) The $E_p$ dependence of the magnetic diffraction profiles measured when the spin flipper is on and off. (b) Comparison of the peak-height-normalized magnetic diffraction profiles measured after cooling with $E_p=822,0,-822\text{kV}/\text{m}$. The effect of imperfect beam polarization has been corrected (Ref. 16). Solid lines are the least-square fits to Lorentzian squared. A horizontal bar represents the experimental resolution limit.

Figure 3

(Color online) The $E_p$ dependences of (a) $D_{\left(110\right)}$ and $I_{\text{ON}}+I_{\text{OFF}}$, (b) $W_h^{\text{on}/\text{off}}$ and $W_l^{\text{on}/\text{off}}$, and (c) ${\xi }_{\left[110\right]}^{\text{LH}/\text{RH}}$ and ${\xi }_{\left[001\right]}^{\text{LH}/\text{RH}}$. The dashed lines are guides to eyes.

Figure 4

(Color online) [(a)–(c)] Schematic illustrations of the magnetic phase transitions and the magnetic domain structures in CFAO. Pink, green, and purple lozenges represent the directions of the magnetic modulation wave vectors in the PD phase. (d) The relationship between ${\xi }_{\left[110\right]}$ and ${\xi }_{\left[001\right]}$ obtained in the present measurements.