Field-induced transformation of complex spin ordering and magnetodielectric and magnetoelastic coupling in MnGeTeO6

Spin-frustrated systems are well known for exhibiting fascinating and exotic magnetic properties and are often intertwined with other intriguing phenomena. Magnetization and specific-heat studies suggest that the spin-frustrated chiral triangular lattice compound MnGeTeO₆ undergoes a long-range antiferromagnetic transition below the N\'eel temperature (TN) {~} 9 K, which is further validated in the neutron powder-diffraction (NPD) study. In the absence of an external magnetic field $(H)$, analysis of NPD data reveals a complex incommensurate spin structure, characterized by a mixture of helical and cycloidal spin orderings with a propagation vector of k=(1/3, 1/3, 0.184). Upon the application of H, this spin ordering transforms into a conical spin structure, which is manifested as a metamagnetic transition in the isothermal magnetization $(M)$ curve when H exceeds {~} 0.9 T. Total energy calculations and estimation of various exchange-interaction energies $(J)$ by density-functional theory calculations also support the formation of such a complex spin ordering. Moreover, a pronounced dielectric (ε^') anomaly is observed near TN, which is suppressed considerably under H. The variation of ε^' with increasing H closely reflects the Δε^'4pt0ex∝ M² scaling behavior in the low-H regime, thus indicating a higher-order magnetoelectric coupling. Moreover, synchrotron x-ray diffraction reveals an isostructural distortion below TN, suggesting magnetoelastic coupling as a trigger for the dielectric anomaly.