Resonant Quantum Magnetodielectric Effect in Multiferroic Metal-Organic Framework [CHNH]Co(HCOO).

The observation of both resonant quantum tunneling of magnetization (RQTM) and resonant quantum magnetodielectric (RQMD) effect in the perovskite multiferroic metal-organic framework [CHNH]Co(HCOO).is reported. An intrinsic magnetic phase separation emerges at low temperatures due to the hydrogen-bond-modified long-range super-exchange interaction, leading to the coexistence of canted antiferromagnetic order and single-ion (Co) magnets.

Discovery of a long-ranged charge order with 1/4 Ge1-dimerization in an antiferromagnetic Kagome metal.

Exotic quantum states arise from the interplay of various degrees of freedom such as charge, spin, orbital, and lattice. Recently, a short-ranged charge order (CO) was discovered deep inside the antiferromagnetic phase of Kagome magnet FeGe, exhibiting close relationships with magnetism. Despite extensive investigations, the CO mechanism remains controversial, mainly because the short-ranged behavior hinders precise identification of CO superstructure.

Annealing-Tunable Charge Density Wave in the Magnetic Kagome Material FeGe.

The unprecedented phenomenon that a charge density wave (CDW) emerges inside the antiferromagnetic (AFM) phase indicates an unusual CDW mechanism associated with magnetism in FeGe. Here, we demonstrate that both the CDW and magnetism of FeGe can be effectively tuned through postgrowth annealing treatments. Instead of the short-range CDW reported earlier, a long-range CDW order is realized below 110 K in single crystals annealed at 320 °C for over 48 h.

Large Magneto-Transverse and Longitudinal Thermoelectric Effects in the Magnetic Weyl Semimetal TbPtBi.

Magnetic topological semimetals provide new opportunities for power generation and solid-state cooling based on thermoelectric (TE) effect. The interplay between magnetism and nontrivial band topology prompts the magnetic topological semimetals to yield strong transverse TE effect, while the longitudinal TE performance is usually poor. Herein, it is demonstrated that the magnetic Weyl semimetal TbPtBi has high value for both transverse and longitudinal thermopower with large power factor (PF).

Atomic-Scale Visualization and Quantification of Configurational Entropy in Relation to Thermal Conductivity: A Proof-of-Principle Study in -GeSbTe.

It remains a daunting task to quantify the configurational entropy of a material from atom-revolved electron microscopy images and correlate the results with the material's lattice thermal conductivity, which strides across statics, dynamics, and thermal transport of crystal lattice over orders of magnitudes in length and time. Here, a proof-of-principle study of atomic-scale visualization and quantification of configurational entropy in relation to thermal conductivity in single crystalline trigonal GeSbTe (aka -GeSbTe) with native atomic site disorder is reported. A concerted effort of large -GeSbTe single crystal growth, in-lab developed analysis procedure of atomic column intensity, the visualization and quantification of configurational entropy including corresponding modulation, and thermal transport measurements enable an entropic "bottom-up" perspective to the lattice thermal conductivity of -GeSbTe.

Mode-Resolved Detection of Magnetization Dynamics Using X-ray Diffractive Ferromagnetic Resonance.

Collective spin excitations of ordered magnetic structures offer great potential for the development of novel spintronic devices. The present approach relies on micromagnetic models to explain the origins of dynamic modes observed by ferromagnetic resonance (FMR) studies, since experimental tools to directly reveal the origins of the complex dynamic behavior are lacking. Here we demonstrate a new approach which combines resonant magnetic X-ray diffraction with FMR, thereby allowing for a reconstruction of the real-space spin dynamics of the system.

Measurement of the angle dependence of magnetostriction in pulsed magnetic fields using a piezoelectric strain gauge.

We present a high resolution method for measuring magnetostriction in millisecond pulsed magnetic fields at cryogenic temperatures with a sensitivity of . The sample is bonded to a thin piezoelectric plate such that when the sample's length changes, it strains the piezoelectric and induces a voltage change. This method is more sensitive than a fiber-Bragg grating method.

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.

Realization of Large Electric Polarization and Strong Magnetoelectric Coupling in BiMn Cr O.

Magnetoelectric multiferroics have received much attention in the past decade due to their interesting physics and promising multifunctional performance. For practical applications, simultaneous large ferroelectric polarization and strong magnetoelectric coupling are preferred. However, these two properties have not been found to be compatible in the single-phase multiferroic materials discovered as yet.

Giant magnetoelectric effects achieved by tuning spin cone symmetry in Y-type hexaferrites.

Multiferroics materials, which exhibit coupled magnetic and ferroelectric properties, have attracted tremendous research interest because of their potential in constructing next-generation multifunctional devices. The application of single-phase multiferroics is currently limited by their usually small magnetoelectric effects. Here, we report the realization of giant magnetoelectric effects in a Y-type hexaferrite BaSrMgFeO single crystal, which exhibits record-breaking direct and converse magnetoelectric coefficients and a large electric-field-reversed magnetization.

Electrochemical-reaction-induced synaptic plasticity in MoO-based solid state electrochemical cells.

Solid state electrochemical cells with synaptic functions have important applications in building smart-terminal networks. Here, the essential synaptic functions including potentiation and depression of synaptic weight, transition from short- to long-term plasticity, spike-rate-dependent plasticity, and spike-timing-dependent plasticity behavior were successfully realized in an Ag/MoO/fluorine-doped tin oxide (FTO) cell with continual resistance switching. The synaptic plasticity underlying these functions was controlled by tuning the excitatory post-synaptic current (EPSC) decay, which is determined by the applied voltage pulse number, width, frequency, and intervals between the pre- and post-spikes.

A multilevel nonvolatile magnetoelectric memory.

The coexistence and coupling between magnetization and electric polarization in multiferroic materials provide extra degrees of freedom for creating next-generation memory devices. A variety of concepts of multiferroic or magnetoelectric memories have been proposed and explored in the past decade. Here we propose a new principle to realize a multilevel nonvolatile memory based on the multiple states of the magnetoelectric coefficient (α) of multiferroics.

Uniaxial ferroelectric quantum criticality in multiferroic hexaferrites BaFe12O19 and SrFe12O19.

BaFe12O19 is a popular M-type hexaferrite with a Néel temperature of 720 K and is of enormous commercial value ($3 billion/year). It is an incipient ferroelectric with an expected ferroelectric phase transition extrapolated to lie at 6 K but suppressed due to quantum fluctuations. The theory of quantum criticality for such uniaxial ferroelectrics predicts that the temperature dependence of the electric susceptibility χ diverges as 1/T(3), in contrast to the 1/T(2) dependence found in pseudo-cubic materials such as SrTiO3 or KTaO3.

Moisture effects on the electrochemical reaction and resistance switching at Ag/molybdenum oxide interfaces.

An important potential application of solid state electrochemical reactions is in redox-based resistive switching memory devices. Based on the fundamental switching mechanisms, the memory has been classified into two modes, electrochemical metallization memory (ECM) and valence change memory (VCM). In this work, we have investigated a solid state electrochemical cell with a simple Ag/MoO3-x/fluorine-doped tin oxide (FTO) sandwich structure, which shows a normal ECM switching mode after an electroforming process.

Quantum electric-dipole liquid on a triangular lattice.

Geometric frustration and quantum fluctuations may prohibit the formation of long-range ordering even at the lowest temperature, and therefore liquid-like ground states could be expected. A good example is the quantum spin liquid in frustrated magnets. Geometric frustration and quantum fluctuations can happen beyond magnetic systems.

Observation of Magnetoelectric Multiferroicity in a Cubic Perovskite System: LaMn(3)Cr(4)O(12).

Magnetoelectric multiferroicity is not expected to occur in a cubic perovskite system because of the high structural symmetry. By versatile measurements in magnetization, dielectric constant, electric polarization, neutron and x-ray diffraction, Raman scattering, as well as theoretical calculations, we reveal that the A-site ordered perovskite LaMn(3)Cr(4)O(12) with cubic symmetry is a novel spin-driven multiferroic system with strong magnetoelectric coupling effects. When a magnetic field is applied in parallel (perpendicular) to an electric field, the ferroelectric polarization can be enhanced (suppressed) significantly.

Nonvolatile electric-field control of magnetization in a Y-type hexaferrite.

The magnetoelectric effects in multiferroic materials enable the mutual control of electric polarization by a magnetic field and magnetization by an electric field. Nonvolatile electric-field control of magnetization is extremely important for information storage applications, but has been rarely realized in single-phase multiferroic materials. Here we demonstrate the prominent direct and converse magnetoelectric effects in the Y-type hexaferrite BaSrCoZnFe11AlO22 single crystal.

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.

Quantum tunneling of magnetization in a metal-organic framework.

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.