The coexistence of both electric and magnetic orders in some metal-organic frameworks (MOFs) has yielded a new class of multiferroics beyond inorganic materials. However, the coupling between two orders in multiferroic MOFs has not been convincingly verified yet. Here we present clear experimental evidences of cross coupling between electric and magnetic orders in a multiferroic MOF [(CH₃)₂NH₂]Fe(HCOO)₃ with a perovskite structure. The dielelectric constant exhibit a hump just at the magnetic ordering temperature T_N. Moreover, both the direct (magnetic field control of dielectric properties) and converse (electric field control of magnetization) magnetoelectric effects have been observed in the multiferroic state. This work opens up new insights on the origin of ferroelectricity in MOFs and highlights their promise as magnetoelectric multiferroics.

Although the magnetoelectric effects - the mutual control of electric polarization by magnetic fields and magnetism by electric fields, have been intensively studied in a large number of inorganic compounds and heterostructures, they have been rarely observed in organic materials. Here we demonstrate magnetoelectric coupling in a metal-organic framework [(CH₃)₂NH₂]Mn(HCOO)₃ which exhibits an order-disorder type of ferroelectricity below 185 K. The magnetic susceptibility starts to deviate from the Curie-Weiss law at the paraelectric-ferroelectric transition temperature, suggesting an enhancement of short-range magnetic correlation in the ferroelectric state. Electron spin resonance study further confirms that the magnetic state indeed changes following the ferroelectric phase transition. Inversely, the ferroelectric polarization can be improved by applying high magnetic fields. We interpret the magnetoelectric coupling in the paramagnetic state in the metal-organic framework as a consequence of the magnetoelastic effect that modifies both the superexchange interaction and the hydrogen bonding.

We have fabricated $c$-axis Josephson junctions on single crystals of ${\mathrm{Ba}}_{1-x}{\mathrm{K}}_x{\mathrm{Fe}}_2{\mathrm{As}}_2$ by using Pb as the counterelectrode in two geometries, planar and point contact. Junctions in both geometries show resistively shunted junction $I\mathrm{\text{−}}V$ curves below the $T_C$ of the counterelectrode. Microwave induced steps were observed in the $I\mathrm{\text{−}}V$ curves, and the critical currents are suppressed with an in-plane magnetic field with well-defined modulation periods indicating that the Josephson current is flowing in a manner consistent with the small to intermediate sized junction limit. $I_C{R}_N$ products of up to 0.3 mV have been observed in these junctions at 4.2 K. The observation of Josephson coupling along the $c$ axis between ${\mathrm{Ba}}_{1-x}{\mathrm{K}}_x{\mathrm{Fe}}_2{\mathrm{As}}_2$ and a conventional superconductor suggests the existence of an $s$-wave symmetry in this class of iron pnictide superconductors.

Resonant quantum tunneling of magnetization has been observed in a hybrid metal-organic framework where an intrinsic magnetic phase separation leads to the coexistence of long-range canted antiferromagnetic order and isolated single-ion quantum magnets. This unusual magnetic phenomenon is well interpreted based on a selective long-distance superexchange model in which the exchange interaction between transition metal ions through an organic linker depends on the position of hydrogen bonds. Our work not only extends the resonant quantum tunneling of magnetization to a new class of materials but also evokes the important role of hydrogen bonding in organic magnetism.

The magnetic properties and magnetocaloric effect in TmGa compound are investigated. TmGa exhibits two successive magnetic transitions: ferromagnetic-antiferromagnetic at T_FA = 12 K and antiferromagnetic-paramagnetic transition at T_N = 15 K. Under field changes of 1 and 2 T, giant reversible values of magnetic entropy change (12.9 and 20.6 J/kg K) and large values of refrigerant capacity (69 and 149 J/kg) are observed, respectively. Additionally, the maximal values of adiabatic temperature change are 3.2 and 5 K for field changes of 1 and 2 T, respectively. The TmGa compound with excellent magnetocaloric effect is expected to have effective applications in low temperature magnetic refrigeration.

A giant low field reversible magnetocaloric effect has been observed in TmCuAl compound around 4 K, which is the boiling point of helium. The maximum value of magnetic entropy change (−ΔS_M^max) and adiabatic temperature change (ΔT_ad^max) is 17.2 J/Kg K and 4.6 K without thermal and field hysteresis loss, for field changes of 0–2 T, respectively. Especially, the giant value of −ΔS_M^max (12.2 J/Kg K) is obtained for a field change of 0-1 T. The results indicate that the TmCuAl compound could be considered as a good candidate material for low-temperature and low-field magnetic refrigerant.