Field-induced transformation of ellipsoidal cycloidal to conical spin order and coupled magnetodielectric effect in a triangular antiferromagnet MnGeTeO6

Yu-Hao Chang^1*, Arkadeb Pal¹, Tsung-Wen Yen¹, Chin-Wei Wang², Meng-Jung Hsieh³, Jiunn-Yuan Lin^3,4, Chi-Yi Huang¹, Yi-Jing Chen¹, Ting-Wei Kuo¹, Ajay Tiwari¹, D. Chandrasekhar Kakarla¹, Hung-Duen Yang^1,5

¹物理系, 國立中山大學, 高雄市, Taiwan
²中子小組, 國家同步輻射研究中心, 新竹, Taiwan
³物理系, 國立陽明交通大學, 新竹, Taiwan
⁴新世代功能性物質研究中心, 國立陽明交通大學, 新竹, Taiwan
⁵晶體中心, 國立中山大學, 高雄市, Taiwan

* Presenter:Yu-Hao Chang, email:cassis88855@gmail.com

Triangular antiferromagnetic systems are well-known for exhibiting fascinating and exotic magnetic properties, which are often intertwined with other intriguing phenomena. Here, we report comprehensive magnetic and dielectric property studies on a layered triangular lattice antiferromagnet MnGeTeO6, which is polar in nature. The bulk magnetization and specific heat studies suggested that the present system undergoes a long-range antiferromagnetic transition below TN ~ 9.5 K, which was further validated by the neutron powder diffraction (NPD) study. The NPD data analysis yielded an incommensurate ellipsoidal cycloidal spin structure with a propagation vector k = (0.33, 0.359, 0.18) in the absence of a magnetic field. Interestingly, a field-induced metamagnetic transition in the isothermal magnetization (M) curve was observed near a critical magnetic field of Hc ~ 1.2 T, which was associated with a spin structure change from ellipsoidal cycloidal to a conical spin order as evidenced by field-dependent NPD measurements. Moreover, a pronounced dielectric anomaly was observed near TN, which was largely suppressed under a magnetic field, thus demonstrating a clear magnetodielectric effect. The magnetic field variation of dielectric constant (ε') closely followed Δε'∝M^2 scaling behavior, thus indicating a higher-order magnetoelectric coupling.

Keywords: Magnetoelectric coupling, Frustrated triangular lattice, Conical and spiral spin texture