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Possible signatures of ferroelectricity in antiferromagnetically ordered zig-zag spin chain

Unconventional orderings of spin may provide a way to form multiferroic phases. For instance, spiral magnetic orders can break the space inversion symmetry and create electric dipoles which is a prerequisite for ferroelectric ordering [1]. One such candidate system is the zig-zag spin chain β-TeVO4 which has a complex magnetic phase diagram at low temperatures. From the paramagnetic high-temperature phase, the system enters the antiferromagnetic incommensurate spin-density wave phase at TN1=4.65 K. Then, at TN2=3.28 K it forms the so-called spin stripes which establish as a second incommensurate spin-density wave is superimposed on top of the first one. Finally, the difference between their two wave vectors disappears at TN3=2.26 K and the system enters its ground state – the vector chiral phase. Interestingly, at this last phase transition the electric dipoles become allowed by crystal symmetry. [2, 3, 4] In this work we investigate the possibility of ferroelectricity in the spin-ordered phases of β-TeVO4 using dielectric spectroscopy and static polarization measurements in the presence of external magnetic field. We discuss the obtained nonlinear dielectric properties in the context of its magnetic phase diagram. [1] K. F. Wang, J. M. Liu, and Z. F. Ren, Adv. Phys 58, (2009), 321–448 [2] M. Pregelj, A. Zorko, O. Zaharko, H. Nojiri, H. Berger, L. C. Chapon, and D. Arcon, Nature Communications 6 (2015), 10.1038/ncomms8255. [3] M. Pregelj, O. Zaharko, M. Herak, M. Gomilsek, A. Zorko, L. C. Chapon, F. Bourdarot, H. Berger, and D. Arcon, Phys. Rev. B 94, 081114 (2016). [4] M. Pregelj, A. Zorko, M Gomišlek, M. Klanjšek, O. Zaharko, J. S White, H. Luetkens, F. Coomer, T. Ivek, D. Rivas-Góngora, H. Berger, D. Arčon, npj Quantum Materials 4, 22 (2019)

spin chain, vector chiral order, magnetoelectric, electric polarization, dielectric response

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