The multiferroic nature of the honeycomb-lattice $\mathrm{M}{\mathrm{n}}_2{\mathrm{V}}_2{\mathrm{O}}_7$ was investigated through detailed temperature, high-pressure, and magnetic-field-dependent measurements. A first-order martensiticlike structural phase transition with the thermal hysteresis associated with magnetic, heat-capacity, and dielectric anomalies was observed between $T_{Mh}$ (303 K) and $T_{Mc}$ (291 K). External pressure up to 15.41 kbar suppresses the thermal hysteresis in the magnetization data, indicating that the high-temperature β-phase persists down to the lower temperature under 15.41 kbar. Furthermore, isothermal capacitance-stress hysteresis loops along with crystallographic Aizu notation of $2/mF\overline{1}$ supports a martensitic phase transition driving ferroelastic ordering near or below room temperature. At low temperature, a long-range antiferromagnetic ordering was observed at $T_N\sim 17\mathrm{K}$. With increasing the external pressure up to 15.41 kbar, 100% enhancement of $T_N$ was observed and a metamagnetic transition at 5 K was enhanced near 3 T. High-field magnetization study up to 60 T induces multiple metamagnetic transitions below $T_N$. Below $T_N$, a magnetostriction induced magnetoelectric coupling was observed and further supported by the temperature-dependent x-ray studies. Taking these comprehensive research findings into account, we established that $\mathrm{M}{\mathrm{n}}_2{\mathrm{V}}_2{\mathrm{O}}_7$ is a unique multifunctional material with the coexistence of ferroelastic and antiferromagnetic orderings and with weak magnetoelectric coupling.

• Received 17 April 2020
• Revised 1 July 2020
• Accepted 31 July 2020

DOI:https://doi.org/10.1103/PhysRevB.102.075130