Interplay between the magnetic and electric degrees of freedom in multiferroic Co3TeO6

Abstract

Neutron diffraction, magnetic susceptibility, specific heat, and dielectric constant measurements of single crystal Co 3 TeO 6 have been measured to study the interplay between the ferroelectricity and magnetic order. Long range incommensurate magnetic order develops below T M1 =26 K, which is followed by three additional zero-field phase transitions at T M2 =19.5 K, T M3 =18 K, and T M4 =16 K where the incommensurate order changes and commensurate order develops. In magnetic fields up to 14 T we find that the magnetic intensities and incommensurate wave vector are dramatically altered as ferroelectricity develops, with a fifth abrupt transition around 10 T. The overall behavior characterizes Co 3 TeO 6 as a type-II multiferroic.Ferroelectricity is a physical phenomenon where spontaneous electrical polarization P appears below a certain temperature T C . Ferroelectric order can arise in a number of ways, such as from a structural change, a spin-exchange interaction, or spin-orbit interaction that triggers relative displacements of the positive and negative ions. 1-6 Multiferroics, where both ferroelectric and magnetic order coexist, are quite uncommon, but are of particular interest both to understand the fundamental interactions between the two types of order as well as for the potential for practical applications. 7-9 For conventional (type-I, or proper) ferroelectrics the two types of order must be associated with different atoms, with generally a weak interaction between the two order parameters. For type-II (improper) ferroelectrics, on the other hand, the ferroelectric displacements

Complex magnetic incommensurability and electronic charge transfer through the ferroelectric transition in multiferroic Co3TeO6

“…3 ), with a modulation vector of q = (0.357, 0.103, 0.087) for the magnetic propagation vector. In contrast to the previous data taken in a single scattering plane 14 , the present experiments demonstrate that all three components of the ordering wave vector are incommensurate, along with second-order ICM Bragg peaks that are also magnetic. The Co spins in Layer A, on the other hand, develop a simple CM antiferromagnetic order with Γ 4 symmetry at zero wave vector.…”

“…We remark that the change in the (600) Bragg intensity of this single crystal below 16 K reported in ref. 14 originates from the relief of extinction in this high quality crystal as discussed previously (shown in Fig. 10b of ref.…”

“…As the temperature is lowered, the system initially orders at T M1 = 26 K with a fully ICM magnetic structure, followed by a separate CM component ordering at T M2 = 19.5 K coexisting with the ICM magnetic order, a ferroelectric transition at T M3 = 18 K coupled to a change in the magnetic structures, and finally a transition at T M4 = 15 K into the magnetic ground state. We note that T M4 was defined as 16 K in our previous reports 14 , 17 , while the present results reveal that this transition is better defined by 15 K, the temperature below which the k component of the ICM structure reappears. These transitions are naturally linked to the crystal geometry, where Co 3 TeO 6 crystallizes into a monoclinic symmetry with the space group C2 / c , with 36 Co ions in a chemical unit cell 9 , 17 .…”

“…Apparently, the Co spins in Layer A and in Layer B order separately, reflecting a weak interlayer magnetic coupling for Co 3 TeO 6 . The two magnetic transitions found 2, 9, 13, 17 are the result of the ordering of the Co spins in the zigzag chains in Layer B into an ICM spin arrangement at T M1  = 26 K, and the separate ordering of the Co spins in the honeycomb web in Layer A into a CM spin structure at T M2  = 19.5 K. Clearly, the modulation vector q  = ( q h , q k , q l ) of the satellite reflections is very sensitive to temperature as previously discussed 14 .

Figure 4Neutron-diffraction intensity maps in the ( h 0 l ) scattering plane near the (203) Bragg position observed at ( a ) 22.5 K, ( b ) 16.5 K, and ( c ) 3 K. The strong powder ring is from the Al sample holder. Below the initial ordering at T M1  = 26 K there is no detectable intensity at the commensurate (203) Bragg position at 22.5 K ( a ), but two satellite magnetic reflections are revealed arising from the development of incommensurate magnetic order.

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“…Single crystals of Co 3 TeO 6 were synthesized through chemical vapor transport redox reactions as described previously 14, 17 . The single crystal used in the present measurements was the same as in our previous work, and weighed 101 mg with a size of 14.1 × 2.2 × 0.9 mm 3 .…”