| Summary: | The triangular based antiferromagnet α-NaFeO2 has been studied by magnetization, dielectric, and neutron diffraction measurements as a function of temperature and magnetic field. The appropriate (HâT) phase diagram was constructed revealing a complex behavior due to a competition between several magnetic phases. In zero field, the system undergoes a sequence of magnetostructural transitions; initially from paramagnetic R3̄m1†phase to the incommensurate spin density wave (ICM1) at TN1=11 K with the nonpolar (3+1) magnetic superspace group C2/m1â€(0, Î,12)s0s, then, below TN2=7.5 K, the ICM1 phase coexists with the polar cycloidal ordering (ICM2) possessing the Cm1â€(0,Î,12)0s superspace symmetry and finally the commensurate collinear ordering (CM) with the nonpolar magnetic space group Pa21/m develops below TN3=5.5 K as the ground state of the system. A small amount of ICM2 coexists with the ICM1 and CM phases resulting in a nonzero measured polarization below TN2. Magnetic field destabilizes the collinear ground state and promotes the polar ICM2 phase resulting in a drastic increase of the polarization. The symmetry of the zero field cycloidal structure allows the two orthogonal components p1ârij×(Si×Sj) and p2â Si×Sj to contribute to the macroscopic polarization through the inverse DM effect. The applied magnetic field reduces the symmetry of the ICM2 phase down to the triclinic P1(α,)0, resulting in admixture of another cycloidal and helical components both generating magnetic field switchable polarization p3 perpendicular to p1 and p2. © 2014 American Physical Society.
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