Magnetodielectric Effect in a Triangular Dysprosium Single-Molecule Toroics.

Single-molecule toroics are molecular magnets with vortex distribution of magnetic moments. The coupling between magnetic and electric properties such as the magnetodielectric effect will provide potential applications for them. Herein, the observation of significant magnetodielectric effect in a triangular Dy3 crystal with toroidal magnetic moment and multiple magnetic relaxations is reported. The analysis of magnetic and electric properties implies that the magnetodielectric effect is closely related to the strong spin-lattice coupling, magnetic interactions of Dy3+ ions, as well as molecular packing models.

Electrical detection and modulation of magnetism in a Dy-based ferroelectric single-molecule magnet.

Electrical control of magnetism in single-molecule magnets with peculiar quantum magnetic behaviours has promise for applications in molecular electronics and quantum computing. Nevertheless, such kind of magnetoelectric effects have not been achieved in such materials. Herein, we report the successful realization of significant magnetoelectric effects by introducing ferroelectricity into a dysprosium-based single-molecule magnet through spatial cooperation between flexible organic ligands and halide ions. The stair-shaped magnetization hysteresis loop, alternating current susceptibility, and magnetic relaxation can be directly modulated by applying a moderate electric field. Conversely, the electric polarization can be modulated by applying a small magnetic field. In addition, a resonant magnetodielectric effect is clearly observed, which enables detection of quantum tunnelling of magnetization by a simple electrical measurement. The integration of ferroelectricity into single-molecule magnets not only broadens the family of single-molecule magnets but also makes electrical detection and modulation of the quantum tunnelling of magnetization a reality.

Ferroelectric Single-Molecule Magnet with Toroidal Magnetic Moments.

Materials that coexist magnetic and electric properties on the molecular scale in single-molecule magnets (SMMs) with peculiar quantum behaviors have promise in molecular electronics and spintronics. Nevertheless, such molecular materials are limited in potentials because their magnetic signal cannot be transformed into an electrical signal through magnetoresistance or Hall effects for their high insulativity. The discovery of an entirely new material, ferroelectric SMMs (FE SMMs) is reported. This FE SMM also shows single-molecule magnetic behaviors, toroidal magnetic moments, and room-temperature ferroelectricity. The toroidal moment is formed by a vortex distribution of magnetic dipoles in triangular Dy3 clusters. The analysis of ac magnetic susceptibility reveals the coexistence of three distinct magnetic relaxation processes at low temperatures. The ferroelectricity is introduced by incorporating polar alcohol molecules in the structure, which is confirmed by the X-ray diffraction and optical second harmonic generation (SHG) measurements. Moreover, the dielectric measurements reveal a ferroelectric-to-ferroelectric phase transition around 150 K due to the symmetry change from Pc to Pna21 . The coexistence of toroidal moment and ferroelectricity along with quantum magnetism in the rare-earth single-molecule magnets yields a unique class of multiferroics.

Magnetic-Field Tuning of Hydrogen Bond Order-Disorder Transition in Metal-Organic Frameworks.

The ordering of polar hydrogen bonds may break space inversion symmetry and induce ferroelectricity or antiferroelectricity. This process is usually immune to external magnetic fields so that magnetic control of hydrogen bonds is very challenging. Here we demonstrate that the ordering of hydrogen bonds in the metal-organic frameworks [(CH_{3})_{2}NH_{2}]M(HCOO)_{3} (M=Fe, Co) can be manipulated by applying magnetic fields. After cooling in a high magnetic field, the order-disorder transition of hydrogen bonds shifts to a lower or higher temperature, depending on antiferroelectricity or ferroelectricity induced by hydrogen bond ordering. Besides, the order-disorder transition leads to a giant thermal expansion, exceeding ∼3.5×10^{4} and ∼2×10^{4} ppm for M=Fe and Co, respectively, which is much higher than that of inorganic ferroelectrics. The influence of magnetic field on hydrogen bond ordering is discussed in terms of the magnetoelastic coupling.

Multiferroicity and magnetoelectric coupling in the paramagnetic state of the metal-organic framework [(CH3)2NH2]Ni(HCOO)3.

The metal-organic framework [(CH3)2NH2]Ni(HCOO)3 (DMA-Ni) has an ABX3 perovskite-like structure. At T C ~ 181 K, DMA-Ni displays a first-order ferroelectric transition, which is triggered by the disorder-order transition of hydrogen bonds. In addition, this compound exhibits a spin-canted antiferromagnetic order below T N ~ 37.6 K through the long-distance superexchange interaction, and a spin-reorientation transition appears near 15 K. The coexistence of magnetic and ferroelectric orders at low temperature testifies the multiferroic properties of DMA-Ni. Besides, the magnetoelectric (ME) coupling exists in the paramagnetic state, where the ferroelectric polarization can be modified by applying high magnetic fields. This behavior is attributed to the local magnetostriction effect.

Observation of Magnetodielectric Effect in a Dysprosium-Based Single-Molecule Magnet.

Materials that possess coupled magnetic and electric properties are of significant interest because of their potential use in next-generation magnetoelectric devices such as digital information storage. To date, the magnetoelectric materials that have been studied in-depth have been limited mainly to inorganic oxides such as perovskite oxides. Molecular materials are a promising alternative because their magnetic and electric elements can be combined together at the molecular level via relatively simple molecular designs. Here, we report the coupling of magnetic and electric properties through a magnetodielectric (MD) effect in a single-crystal sample, which is constructed from dysprosium(III) single-molecule magnets (SMMs). The MD effect originates from intrinsic spin-lattice coupling of the dysprosium(III) ion within the sample. This is the first observation of the MD effect in a SMM-based material, which could pave the way toward the synthesis of advanced materials that combine distinct magnetic and electric properties using molecular chemistry for use in molecular devices with nanoscale size.