Li-Qin Yan

Cross coupling between electric and magnetic orders in a multiferroic metal-organic framework

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 TN. 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.

Positive colossal magnetoresistance in a multilayer p–n heterostructure of Sr-doped LaMnO3 and Nb-doped SrTiO3

A positive colossal magnetoresistance (CMR) has been discovered in an epitaxial multilayer p–n heterostructure fabricated with Sr-doped LaMnO3 and Nb-doped SrTiO3 by laser molecular-beam epitaxy. In contrast to the negative CMR of the LaMnO3 compound family, positive CMR is observed in the temperature range from 100 to 300 K. The largest value of the magnetoresistance (MR) ratio (ΔR/R0,ΔR=RH−R0), 517%, is one order of magnitude larger than that of simple p–n junctions of the same materials previously reported. A very large MR ratio, 297%, remains in a low field of 0.01 T. Even at a temperature as high as 300 K, a MR ratio as large as 17.3% is still observed.

Observation of Resonant Quantum Magnetoelectric Effect in a Multiferroic Metal-Organic Framework.

A resonant quantum magnetoelectric coupling effect has been demonstrated in the multiferroic metal-organic framework of [(CH3)2NH2]Fe(HCOO)3. This material shows a coexistence of a spin-canted antiferromagnetic order and ferroelectricity as well as clear magnetoelectric coupling below TN ≈ 19 K. In addition, a component of single-ion quantum magnets develops below ∼ 8 K because of an intrinsic magnetic phase separation. The stair-shaped magnetic hysteresis loop at 2 K signals resonant quantum tunneling of magnetization. Meanwhile, the magnetic field dependence of dielectric permittivity exhibits sharp peaks just at the critical tunneling fields, evidencing the occurrence of resonant quantum magnetoelectric coupling effect. This resonant effect enables a simple electrical detection of quantum tunneling of magnetization.

Low magnetic field reversal of electric polarization in a Y-type hexaferrite

We report on the magnetically tunable ferroelectricity and giant magnetoelectric sensitivity up to 250u2009K in a Y-type hexaferrite, BaSrCoZnFe11AlO22. Not only the magnitude but also the sign of electric polarization can be effectively controlled by applying low magnetic fields (a few hundreds of Oe) that modifies the spiral magnetic structures. The magnetically induced ferroelectricity is stabilized even in zero magnetic field. Decayless reproducible flipping of electric polarization by oscillating low magnetic fields is shown. The maximum linear magnetoelectric coefficient reaches a high value of ∼3.0u2009×u2009103 ps/m at 200u2009K.

Low-field induced giant magnetocaloric effect in TmCuAl compound

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 (-Delta S-M(max)) and adiabatic temperature change (Delta T-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 -Delta S-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

Magnetic-ion-induced displacive electric polarization inFeO5bipyramidal units of(Ba,Sr)Fe12O19hexaferrites

Electric polarization in conventional ferroelectric oxides usually involves nonmagnetic transition-metal ions with an empty d shell (the d

Multiferroicity and magnetoelectric coupling in half-doped manganite La0.5Ca0.5MnO3

^0

Magnetic field reversal of electric polarization and magnetoelectric phase diagram of the hexaferrite Ba1.3Sr0.7Co0.9Zn1.1Fe10.8Al1.2O22

rule). Here we unravel a new mechanism for local electric dipoles based on magnetic Fe

Magnetic properties and magnetic entropy change in spinels (Cd,M)Cr2S4 with M=Cu or Fe

^{3+}

Persistent multiferroicity without magnetoelectric effects in CuO

(3d