Strongly correlated materials with multiple order parameters provide unique insights into the fundamental interactions in condensed matter systems and present opportunities for innovative technological applications. A class of antiferromagnetic honeycomb lattices compounds, A4B2O9 (A = Co, Fe, Mn; B = Nb, Ta), have been explored owing to the occurrence of linear magnetoelectricity. From our investigation of magnetoelectricity on single crystalline Co4Ta2O9, we discovered strongly nonlinear and antisymmetric magnetoelectric behavior above the spin-flop transition for magnetic fields applied along two orthogonal in-plane directions. This observation suggests that two types of inequivalent Co2+ sublattices generate magnetic-field-dependent ferroelectric polarization with opposite signs. The results motivate fundamental and applied research on the intriguing magnetoelectric characteristics of these buckled-honeycomb lattice materials.

**References:**

[1] N. Lee, D. G. Oh and Y. J. Choi, Scientific Reports, vol. 10, 12362 (2020)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/14735df7b8d80e6faf7c4ad0add6d601.jpg)
Fig. 1 Temperature dependence of the anisotropic ferroelectric polarization. (a–c) T dependence of Pa obtained by integrating the pyroelectric current after poling from 100 to 2 K in at Ha, Hb*, and Hc, respectively. Pa was measured at H = 1, 3, 5, 7 and 9 T. (d–f) T dependence of Pb* measured at Ha = 9 T, Hb*, and Hc, respectively. (g–i) T dependence of Pc measured at Ha = 9 T, Hb*, and Hc, respectively.

![](https://assets.underline.io/uploads/markdown_image/1/image/1dddc0b497f4c43b1b9e466269999736.jpg)
Fig. 2 Comparison of electric and magnetic properties. (a) Hb* dependence of Pa at T = 2 K. (b) Hb* dependence of the magnetodielectric effect along the a axis, MDa (%) = {ε′(H) − ε′(0T)} / ε′(0T) × 100 , measured with AC excitation of Ea = 1 V at f = 100 kHz and T = 2 K. (c) Hb* derivative of Mb* at 2 K.

 Highly nonlinear magnetoelectric effect in buckled honeycomb antiferromagnetic Co4Ta2O9

In rare-earth orthoferrites, strongly correlated order parameters have been thoroughly investigated, which aims to find multiple fuctionalities such as multiferroic or magnetoelectric properties. We have discovered highly anisotropic and nonlinear magnetodielectric effect from detailed measurements of magnetoelectric properties in single-crystalline orthoferrite, ErFeO3. Isothermal dielectric constant varies in shapes and signs depending on the relative orientations between the external electric and magnetic fields, which may be ascribed to the spin-phonon couplings. In addition, a dielectric constant with both electric and magnetic fields along the c axis exhibits two symmetric sharp anomalies, which are closely relevant to the spin-flop transition, below the ordering temperature of Er3+ spins, TEr = 3.4 K. We speculate that the magnetostriction form the exchange couplings between Er3+ and Fe3+ magnetic moments would be responsible for this relationship between electric and magnetic properties. Our results present significant characteristics of the orthoferrite compounds and offer a crucial guide for exploring suitable materials for magnetoelectric functional applications.

**References:**

[1] H. J. Shin, Y.J. Choi and N. Lee, Scientific Reports., 10:11825 (2020)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/5564792e58f2025c698fb955501095ae.jpg)
Magnetodielectric effect of ErFeO3. Magnetodielectric (MD) effect defined as 
MD (%) = (ε′(H)−ε′(0T))/ε′(0T) × 100 for (a)–(c) a (MDa), (d)–(f) b (MDb), and (g)–(i) c (MDc) axes, respectively, at Ha, Hb , and Hc up to ± 9 T and T = 2 K.

![](https://assets.underline.io/uploads/markdown_image/1/image/7b3b7a8f4622c4c168fd19b029722ed0.jpg)
Temperature evolution of magnetodielectric effect along the c axis. (a)–(f) Hc dependence of MDc at T = 2, 2.5, 3, 3.5, 5 and 10 K. (g)–(l) Hc derivative of Mc and dMc/dHc measured at T = 2, 2.5, 3, 3.5, 5 and 10 K.

 Anisotropic and nonlinear magnetodielectric effects in orthoferritre ErFeO3 single crystals

*Session Chair: Stella Skiadopoulou, The University of Dublin Trinity College*

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DP: Multiferroics and Magnetoelectrics: Phenomena, Materials and Transport

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Highly nonlinear magnetoelectric effect in buckled honeycomb antiferromagnetic Co4Ta2O9

Anisotropic and nonlinear magnetodielectric effects in orthoferritre ErFeO3 single crystals

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