Tuning a sign of magnetoelectric coupling in paramagnetic NH(2)(CH(3))(2)Al(1−x)Cr(x)(SO(4))(2) × 6H(2)O crystals by metal ion substitution

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 NH(2)(CH(3))(2)Al(1−x)Cr(x)(SO(4))(2) × 6H(2)O. 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.