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

Abstract

The metal-organic framework [(CH 3 ) 2 NH 2 ]Ni(HCOO) 3 (DMA-Ni) has an ABX 3 perovskitelike 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.

Inorganic–Organic Hybrid Molecular Materials: From Multiferroic to Magnetoelectric

“…Apart from the multiferroic state, the ME effect can exist in any other magnetic orders and even in the paramagnetic state. The PME effect was also observed in the multiferroic MOF [(CH 3 ) 2 NH 2 ]Ni(HCOO) 3 [38] and hybrid organometallic system NH 2 (CH 3 ) 2 Al 1−x Cr x (SO 4 ) 2 × 6H 2 O. [92] Recently, Long et al achieved a strong room-temperature ME coupling (α 31 = ∼100 mV Oe −1 cm −1 ) in a paramagnetic ferroelectric ytterbium (III) coordination complex.…”

“…Many cations such as (NH 4 ) + , [29] (C 3 N 2 H 5 ) + , [30] C(NH 2 ) 3 + , [31] (CH 3 CH 2 NH 3 ) + , [25] (CH 3 NH 2 NH 2 ) + , [46] and (CH 3 NH 3 ) + [28] have been chosen as the A cations. Meanwhile, many divalent metal ions have been placed at the B-site, such as Mn 2+ , [34] Fe 2+ , [35][36] Co 2+ , [28] Ni 2+ , [37,38] Zn 2+ , [86] Cu 2+ , [31] Cd 2+ , [87] Mg 2+ , [88] and Cr 2+ . [80] Cu 2+ [84] and Cr 2+ [80,89] are also famous as Jahn-Teller-active ions.…”

Hydrogen Bond Tuning of Magnetoelectric Coupling in Metal–Organic Frameworks

“…As a result, the magnetic structure of MnNi-MOF can be assigned to canted antiferromagnetic (CAFM). The T N of Mn-MOF is 8.7 K and Ni-MOF is 37 K. , The intermediate magnetic ordering temperature of 13 K represents the modified Mn–O–C–O–Mn superexchange pathway in MnNi-MOF. These magnetic measurements indicate that replacing larger Mn 2+ by smaller Ni 2+ induces significant changes in C–O bonds and O–C–O bond angles of the organic linker HCOO – .…”

“…The similar magnetic field enhancement of polarization was also observed in Ni-MOF. 31 This magnetic field induced enhancement of polarization is an interesting aspect in MOFs and is still under debate. Surprisingly, in MnNi-MOF, the magnetic field suppresses the polarization from 0.91 μC/cm 2 at 0 T to 0.72 μC/cm 2 at 5 T with the negative static ME coefficient estimated to be −496 ps/m.…”

Pressure Effect on Order–Disorder Ferroelectric Transition in a Hydrogen-Bonded Metal–Organic Framework

“…Previous studies have shown that ferroelectric or antiferroelectric phase transitions are triggered by the order–disorder of A site organic cations inside the cavities through hydrogen bonding in [(CH 3 ) 2 NH 2 ] M (HCOO) 3 (M = divalent metal ions)-type compounds. − The organic linkers X bridging metal ions via coordination bonds form three-dimensional soft networks, giving rise to sensitivity to the external pressure which provides plenty of opportunities in control of structure merits and functionality, such as hydrogen bond arrangement, structural phase transition, and melting temperature modification. − …”