Tuning a sign of magnetoelectric coupling in paramagnetic NH2(CH3)2Al1−xCrx(SO4)2 × 6H2O crystals by metal ion substitution

Abstract

Hybrid organometallic systems offer a wide range of functionalities, including magnetoelectric (ME) interactions. However, the ability to design on-demand ME coupling remains challenging despite a variety of host-guest configurations and ME phases coexistence possibilities. Here, we report the effect of metal-ion substitution on the magnetic and electric properties in the paramagnetic ferroelectric NH₂(CH₃)₂Al_1−xCr_x(SO₄)₂ × 6H₂O. Doing so we are able to induce and even tune a sign of the ME interactions, in the paramagnetic ferroelectric (FE) state. Both studied samples with x = 0.065 and x = 0.2 become paramagnetic, contrary to the initial diamagnetic compound. Due to the isomorphous substitution with Cr the ferroelectric phase transition temperature (T_c) increases nonlinearly, with the shift being larger for the 6.5% of Cr. A magnetic field applied along the polar c axis increases ferroelectricity for the x = 0.065 sample and shifts T_c to higher values, while inverse effects are observed for x = 0.2. The ME coupling coefficient α_ME = 1.7 ns/m found for a crystal with Cr content of x = 0.2 is among the highest reported up to now. The observed sign change of α_ME with a small change in Cr content paves the way for ME coupling engineering.