Ferroelectricity in an Ising Chain Magnet

Y. J. Choi, H. T. Yi, S. Lee, Q. Huang, V. Kiryukhin, and S.-W. Cheong

Phys. Rev. Lett. 100, 047601 – Published 29 January 2008

Abstract

We report discovery of collinear-magnetism-driven ferroelectricity in the Ising chain magnet ${Ca}_{3} {Co}_{2 - x} {Mn}_{x} O_{6}$ ( $x \approx 0.96$ ). Neutron diffraction shows that ${Co}^{2 +}$ and ${Mn}^{4 +}$ ions alternating along the chains exhibit an up-up-down-down ( $↑ ↑ ↓ ↓$ ) magnetic order. The ferroelectricity results from the inversion symmetry breaking in the $↑ ↑ ↓ ↓$ spin chain with an alternating charge order. Unlike in spiral magnetoelectrics where antisymmetric exchange coupling is active, the symmetry breaking in ${Ca}_{3} (Co, Mn)_{2} O_{6}$ occurs through exchange striction associated with symmetric superexchange.

Received 13 September 2007

DOI:https://doi.org/10.1103/PhysRevLett.100.047601

Authors & Affiliations

Y. J. Choi¹, H. T. Yi¹, S. Lee¹, Q. Huang², V. Kiryukhin¹, and S.-W. Cheong¹

¹Rutgers Center for Emergent Materials and Department of Physics & Astronomy, 136 Frelinghuysen Road, Piscataway, New Jersey, 08854, USA
²NIST Center for Neutron Research, NIST, Gaithersburg, Maryland 20899, USA

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Vol. 100, Iss. 4 — 1 February 2008

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Images

Figure 1
(a) Ising chains with the up-up-down-down spin order and alternating ionic order, in which electric polarization is induced through symmetric exchange striction. The two possible magnetic configurations leading to the opposite polarizations are shown. The atomic positions in the undistorted chains are shown with dashed circles. (b,c) The crystal structure of the ${Ca}_{3} {CoMnO}_{6}$ chain magnet. The green boxes represent the crystallographic unit cell.Reuse & Permissions
Figure 2
(a) Electric polarization of single crystal ${Ca}_{3} {Co}_{1 - x} {Mn}_{x} O_{6}$ ( $x = 0.96$ ) along the chain direction ( $P ∥ c$ ), taken upon warming. The samples were poled upon cooling from 40 K to 2 K (filled circles), and to 3.1 K (open circles) before the measurement. The data for the 2 K poled sample were collected in various applied magnetic fields, as shown. (b) Temperature dependence of magnetic susceptibility, $χ (T) = M / H$ , measured in an applied magnetic field $H = 0.2 T$ along and perpendicular to the chain direction. The temperature derivative $d χ / d T$ , and zero-field heat capacity ( $C / T$ ) are also shown. (c) The $c$ -axis dielectric constant, $ϵ_{c}$ . Dashed line shows the high-temperature behavior of $ϵ_{c}$ .Reuse & Permissions
Figure 3
(a) $χ (T)$ of polycrystalline ${Ca}_{3} {Co}_{1 - x} {Mn}_{x} O_{6}$ for $H = 0.2 T$ . (b) $ϵ (T)$ of polycrystalline ${Ca}_{3} {Co}_{1 - x} {Mn}_{x} O_{6}$ for $H = 0$ , normalized at $T = 20 K$ . The insets in (a) and (b) show peak positions of $χ (T)$ and $ϵ (T)$ , respectively, for different Mn concentrations. The dashed lines indicate the corresponding peak positions in the $x = 0.96$ single crystal. (c,d) Real and imaginary parts of the AC susceptibility, $χ^{'} (T)$ , and $χ^{''} (T)$ , of the $x = 0.96$ single crystal. The AC magnetic field is 5 Oe, and the frequencies are 0.1, 1 and 10 kHz, as shown. The inset in Fig. 3c shows $\log [f]$ vs inverse temperature for the peaklike features of $χ^{'}$ . The low-temperature feature is shown with filled circles, and the high-temperature feature with open circles.Reuse & Permissions
Figure 4
Observed (symbols) and calculated (line) powder neutron diffraction patterns for polycrystalline ${Ca}_{3} {Co}_{1 - x} {Mn}_{x} O_{6}$ ( $x = 0.95$ ) for $T = 1.4 K$ . The first row of bars below the diffraction pattern indicates the positions of the nuclear Bragg peaks, and the second row depicts the locations of the magnetic Bragg peaks. The blue line shows the difference between the observed and calculated diffraction patterns. The insets show the low-angle patterns for $T = 1.4 K$ , 8 and 20 K, and the refined spin structure.Reuse & Permissions

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