Kun Zhai

Nonvolatile Memory Based on Nonlinear Magnetoelectric Effects

The magnetoelectric effects in multiferroics have a great potential in creating nextgeneration memory devices. We conceive a new concept of non-volatile memories based on a type of nonlinear magnetoelectric effects showing a butterfly-shaped hysteresis loop. The principle is to utilize the states of the magnetoelectric coefficient, instead of magnetization, electric polarization or resistance, to store binary information. Our experiments in a device made of the PMN-PT/Terfenol-D multiferroic heterostructure clearly demonstrate that the sign of the magnetoelectric coefficient can be repeatedly switched between positive and negative by applying electric fields, confirming the feasibility of this principle. This kind of non-volatile memory has outstanding practical virtues such as simple structure, easy operations in writing and reading, low power, fast speed, and diverse materials available. The global information era has been seeking a universal non-volatile random-access memory (NVRAM) for many years. The best-known form of NVRAM today is flash memory. However, some drawbacks of flash memory prevent it from becoming the universal memory. Several competitive technologies are attempting to replace flash memory in certain roles. These include magnetic random access memory (MRAM) [1-3], resistive switching random access memory (RRAM) [4,5], phase change memory (PRAM) [6,7], ferroelectric random access memory (FeRAM) [8-10], and racetrack memory [11]. To date these alternatives of NVRAM have not yet become mainstream in industry because each of them faces certain challenging hurdles. Multiferroics that combine magnetism and ferroelectricity as well as mutual coupling between them [12-15], hold a promise for designing a new generation of memory devices. Several strategies towards a non-volatile magnetoelectric (ME) random access memory or a multiferroic memory have been proposed and explored in the past decade [16-25]. One

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 Ba0.4Sr1.6Mg2Fe12O22 single crystal, which exhibits record-breaking direct and converse magnetoelectric coefficients and a large electric-field-reversed magnetization. We have uncovered the origin of the giant magnetoelectric effects by a systematic study in the Ba2-xSrxMg2Fe12O22 family with magnetization, ferroelectricity and neutron diffraction measurements. With the transverse spin cone symmetry restricted to be two-fold, the one-step sharp magnetization reversal is realized and giant magnetoelectric coefficients are achieved. Our study reveals that tuning magnetic symmetry is an effective route to enhance the magnetoelectric effects also in multiferroic hexaferrites.Control of the electrical properties of materials by means of magnetic fields or vice versa may facilitate next-generation spintronic devices, but is still limited by their intrinsically weak magnetoelectric effect. Here, the authors report the existence of an enhanced magnetoelectric effect in a Y-type hexaferrite, and reveal its underlining mechanism.

Nonvolatile transtance change random access memory based on magnetoelectric P(VDF-TrFE)/Metglas heterostructures

Transtance change random access memory (TCRAM) is a type of nonvolatile memory based on the nonlinear magnetoelectric coupling effects of multiferroics. In this work, ferroelectric P(VDF-TrFE) thin films were prepared on Metglas foil substrates by the sol-gel technique to form multiferroic heterostructures. The magnetoelectric voltage coefficient of the heterostructure can be switched reproducibly to different levels between positive and negative values by applying selective electric-field pulses. Compared with bulk multiferroic heterostructures, the polarization switching voltage was reduced to 7 V. Our facile technological approach enables this organic magnetoelectric heterostructure as a promising candidate for the applications in multilevel TCRAM devices.

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. Because the states of α depends on the relative orientation between magnetization and polarization, one can reach different levels of α by controlling the ratio of up and down ferroelectric domains with external electric fields. Our experiments in a device made of the PMN-PT/Terfenol-D multiferroic heterostructure confirm that the states of α can be well controlled between positive and negative by applying selective electric fields. Consequently, two-level, four-level, and eight-level nonvolatile memory devices are demonstrated at room temperature. This kind of multilevel magnetoelectric memory retains all the advantages of ferroelectric random access memory but overcomes the drawback of destructive reading of polarization. In contrast, the reading of α is nondestructive and highly efficient in a parallel way, with an independent reading coil shared by all the memory cells.

Orthoborates LiCdRE5(BO3)6 (RE = Sm–Lu and Y) with Rare-Earth Ions on a Triangular Lattice: Synthesis, Crystal Structure, and Optical and Magnetic Properties

Single crystals of LiCdY5(BO3)6 were successfully grown from a Li2O-B2O3 flux, and its lanthanide homotypic compounds, LiCdRE5(BO3)6 (RE = Sm-Lu), have been prepared by solid-state reaction. They crystallize in the noncentrosymmetric space group P6522 with cell parameters in the ranges of a = 7.0989(2)-6.9337(1) Å and c = 25.9375(1)-24.8960(6) Å. As a representative example, LiCdY5(BO3)6 features a triangular lattice in the ab plane composed of three distinct crystallographic Y sites. The triangular lattices spaced with the same distance of [Formula: see text]c are further stacked to build three-dimensional frameworks by reinforcement of the isolated planar BO3 groups and distorted LiO4 tetrahedra. Magnetic measurements show that Eu and Sm compounds exhibit typical Van Vleck-type paramagnetism and other rare-earth borates show weak antiferromagnetic behavior. In addition, UV-vis-near-IR diffuse-reflectance and photoluminescence spectra were performed to understand the transition energy levels of active rare-earth ions and their relationships to magnetism.

Spin-induced multiferroicity in the binary perovskite manganite Mn 2 O 3

The ABO3 perovskite oxides exhibit a wide range of interesting physical phenomena remaining in the focus of extensive scientific investigations and various industrial applications. In order to form a perovskite structure, the cations occupying the A and B positions in the lattice, as a rule, should be different. Nevertheless, the unique binary perovskite manganite Mn2O3 containing the same element in both A and B positions can be synthesized under high-pressure high-temperature conditions. Here, we show that this material exhibits magnetically driven ferroelectricity and a pronounced magnetoelectric effect at low temperatures. Neutron powder diffraction revealed two intricate antiferromagnetic structures below 100 K, driven by a strong interplay between spin, charge, and orbital degrees of freedom. The peculiar multiferroicity in the Mn2O3 perovskite is ascribed to a combined effect involving several mechanisms. Our work demonstrates the potential of binary perovskite oxides for creating materials with highly promising electric and magnetic properties.Multiferroic binary oxides with the perovskite structure have been very rare. Here, Cong et al. report magnetically-driven ferroelectricity and a large magnetoelectric effect in a binary perovskite compound Mn2O3 at low temperatures.

Electromagnon in the Z -type hexaferrite ( Ba x Sr 1 − x ) 3 Co 2 Fe 24 O 41

We studied experimentally the high-temperature magnetoelectric

Electromagnon in Y-type hexaferrite BaSrCoZnFe

{({\mathrm{Ba}}_{x}{\mathrm{Sr}}_{1\ensuremath{-}x})}_{3}{\mathrm{Co}}_{2}{\mathrm{Fe}}_{24}{\mathrm{O}}_{41}

_{11}

prepared as ceramics (

AlO

x=0