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)2Al1−xCrx(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 (Tc) 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 Tc to higher values, while inverse effects are observed for x = 0.2. The ME coupling coefficient αME = 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 αME with a small change in Cr content paves the way for ME coupling engineering.
Highlights
Realization of the effective interactions between magnetic moments and electric charges constitutes an important task for modern solid state physics[1,2] and spin electronics[3,4,5,6]
Initial DMAAS crystals usually grow in a monodomain ferroelastic state
If Cr is introduced this tendency is inversed: the samples predominately grow in a polydomain ferroelastic state (Fig. 2). In this case the energy-dispersive X-ray (EDX) analysis of the neighboring domains shows a different content of chromium
Summary
We report the effect of metal-ion substitution on the magnetic and electric properties in the paramagnetic ferroelectric NH2(CH3)2Al1−xCrx(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. In the crystal structures of [NH2(CH3)2]Al1−xCrx(SO4)2 × 6H2O with x = 0.2 and 0.065 octahedra are occupied by statistical mixtures of magnetic Cr− and nonmagnetic Al− atoms With cooling this crystal exhibits a second order phase transition at Tc = 152 K from paraelectric but ferroelastic (T > Tc) to ferroelectric (T < Tc) phases. We report that the incorporated magnetic Cr cations can participate in ME interactions in the [NH2(CH3)2]Al1−xCrx(SO4)2 × 6H2O crystals with ability to tune magneto-electric functionality
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