Search

Domains and domain wall engineering have been extensively explored in ferroic materials for a wide range of applications in nanoelectronics and spintronics. Complex oxides exhibiting strongly correlated properties are model platforms for such studies where response to strain or external stimuli such as electric field, temperature and light can be probed. Here, domains in strained SrMnO3 films, grown on a degenerate semiconductor, allowing for conduction in an out‐of‐plane geometry, are studied using a combination of microscopy probes. Using conductive atomic force microscopy, electrically isolated domains with varying conductance are found and their temporal evolution is investigated. Further, their formation and microstructure are studied using scanning transmission electron microscopy and secondary electron contrast in scanning electron microscopy. An important contribution is establishing that the observed domains are formed by cracks, driven by inhomogeneous strain relaxation throughout the film, resulting in significantly high strain planes. The potential of secondary electrons to detect domain dependent contrast over a large area, ensuing due to the use of a degenerate semiconductor correlates with the conductive properties of the domains and serves as a new direction to probe domains and domain walls in ferroic materials. [ABSTRACT FROM AUTHOR]

Ferro‐rotational (FR) materials, renowned for their distinctive material functionalities, present challenges in the growth of homo‐FR crystals (i.e., single FR domain). This study explores a cost‐effective approach to growing homo‐FR helimagnetic RbFe(SO4)2 (RFSO) crystals by lowering the crystal growth temperature below the TFR threshold using the high‐pressure hydrothermal method. Through polarized neutron diffraction experiments, it is observed that nearly 86% of RFSO crystals consist of a homo‐FR domain. Notably, RFSO displays remarkable stability in the FR phase, with an exceptionally high TFR of ≈573 K. Furthermore, RFSO exhibits a chiral helical magnetic structure with switchable ferroelectric polarization below 4 K. Importantly, external electric fields can induce a single magnetic domain state and manipulate its magnetic chirality. The findings suggest that the search for new FR magnets with outstanding material properties should consider magnetic sulfates as promising candidates. [ABSTRACT FROM AUTHOR]

Herein, the multiferroic perovskite Er0.9La0.1Cr0.8Fe0.2O3 was synthesized using the sol–gel method, and its structure and multiferroic properties were investigated. The magnetic order of Er0.9La0.1Cr0.8Fe0.2O3 was analyzed through magnetic entropy change curves. Furthermore, a four‐sublattice molecular field model was constructed to study the spin reorientation phenomena and explain the differences between various spin redirections through magnetic order correction. This work will provide a new perspective for studying the properties of type II multiferroic materials. [ABSTRACT FROM AUTHOR]

In the present study, SrTiO3 was selected to enhance the multiferroic characteristics of Bi0.88Sm0.12FeO3 (BSF) ceramics. With increasing SrTiO3 content, the principal phase of BSF ceramic transitions from rhombohedral R3c to Pna21. Through DSC and dielectric analysis, it was observed that both the Curie temperature and Néel temperature decreased proportionally with the augmentation of SrTiO3 content. When x =.1, the optimal ferroelectric performance is achieved, and the highest remanent polarization value is 55.47 µC/cm2, significantly surpassing that of BSF ceramics. Moreover, the PFM test results showed that as the substitution content increased, the domains in the BSF ceramic gradually transformed from normal ferroelectric domains to polar nanomicro‐domains. Magnetic and magnetoelectric results show that when x =.1, the best magnetic properties are obtained, Mr = 59.7 emu/mol. The magnetoelectric coefficient αME initially increased and then decreased with the increasing SrTiO3 content, reaching its optimum magnetoelectric properties at x =.1, where αME =.47 mV cm–1 Oe–1. In summary, when the substitution amount of SrTiO3 reaches 10%, the ferroelectric, magnetic, and magnetoelectric properties of BSF ceramics are significantly improved. [ABSTRACT FROM AUTHOR]

BiFeO3‐BaTiO3‐based ceramics are promising multiferroic materials for a wide range of applications. In this paper, the effects of different ionic valence state((Ga0.5Ta0.5)4+, Ta5+) doping on the structure and properties of 0.73BiFeO3‐0.27BaTi1‐y(Ga1‐xTax)yO3 ceramics were investigated. X‐ray diffraction analysis showed that all samples were determined by rhombohedral R3c phase and tetragonal P4mm phase. A frequency‐independent dielectric anomaly with obvious thermal hysteresis was detected in all samples, indicating the first‐order ferroelectric phase transition, and the Curie temperatures were all above 600°C. The ferroelectric analysis found that the doping of donor element Ta reduced the coercive field, with a slight decrease of remanent polarization, which can be attributed to the soft effect of Ta element. Meanwhile, the magnetic properties were enhanced for all samples, with a maximum in 15T (x = 1, y =.015) sample, where Mr =.13 emu/g. According to relevant analysis, high‐valence element substitution can enhance the magnetic properties and reduce the coercive field of BiFeO3, while low‐valence element substitution can reduce dielectric loss. This result points out a way for us to choose appropriate doping elements to improve the performance of BiFeO3 ceramics. [ABSTRACT FROM AUTHOR]

Magnon, a quanta of spin waves, can transport in magnetically ordered insulators without substantial heat dissipation. The recently demonstrated magnon‐mediated spin torque through antiferromagnetic insulators is regarded as a highly efficient approach for electrical manipulation of magnetization. To control the magnon transport in antiferromagnets, a very large magnetic field is required, since antiferromagnets show immunity to external magnetic disturbance. The antiferromagnetic order can be electrically controlled in multiferroic materials via the magnetoelectric coupling between the antiferromagnetic and ferroelectric orders. Here, we report the experimental observation of magnon spin transport through multiferroic BiFeO3 thin films in SrRuO3/BiFeO3/NiFe tri‐layers at room temperature. We find highly efficient magnon current transmission through BiFeO3 thin film with a thickness exceeding 80 nm by the spin pumping measurement. The magnon spin‐torque efficiency in the tri‐layers measured by the spin‐torque ferromagnetic resonance is comparable with that in the SrRuO3/NiFe bilayer. This results suggest multiferroic BiFeO3 to be an excellent platform for investigating the antiferromagnetic magnon transport and developing magnonic devices. [ABSTRACT FROM AUTHOR]

Transition metal perovskite oxide membranes and their unique properties have attracted great attention recently and have been developed into one of the research frontiers in condensed matter physics and materials science. Free of constraint imposed by the underlying substrate, freestanding membranes exhibit extraordinary structural tunability and flexibility far exceeding the bulk materials and epitaxial films clamped on substrates, which substantially extends the explorable regime in the phase diagrams. Moreover, high‐quality oxide membranes, even down to a single unit cell, can be synthesized and stacked/integrated with any materials for novel artificial heterostructures and electronic applications. The exceptional structural tunability and stacking ability in oxide membranes provide new knobs to explore the spontaneous symmetry breaking in oxides, providing a fertile playground for emergent primary ferroic/multiferroic properties and electronic applications. Here, the recent progress is briefly reviewed and the promising outlook for future research in ferroic perovskite oxide membranes and their applications is discussed. [ABSTRACT FROM AUTHOR]

We investigated the ferroelectric switching dynamics as well as the multiferroic and piezoelectric properties of highly a‐oriented epitaxial Bi5Ti3FeO15 (BTFO) thin films on Nb‐doped SrTiO3 single crystal substrates. The BTFO thin films favored highly a‐oriented crystallinity because c‐oriented crystallinity decreased under deposition conditions in which substrate temperature and thin film deposition rate were simultaneously lowered. The highly a‐oriented epitaxial BTFO thin films showed the best ferroelectric properties, whereas the highly c‐oriented epitaxial BTFO thin films showed the best ferromagnetic properties. In particular, the BTFO thin films in which a‐ and c‐oriented crystallinity were properly mixed showed the best piezoelectric properties. [ABSTRACT FROM AUTHOR]

In the present work, Bi0.86Sm0.14FeO3 ceramics with near Pna21 single‐phase structure were obtained by a repeated longtime sintering process, and the dielectric, ferroelectric, and magnetic characteristics were determined together with the magnetoelectric coupling coefficient. The evolution of Pna21 symmetry was revealed by transmission electron microscope analysis, and the ferroelectric transition from Pbnm to Pna21 was determined by differential scanning calorimetry analysis together with the dielectric characterization, and the Curie temperature was determined as 195°C. The saturated polarization–electric field (P–E) hysteresis loop was obtained with Pr = 12.2 μC cm−2, and the unlocking of ferromagnetism was confirmed by the apparent magnetization–magnetic field (M–H) hysteresis loop with Mr = 77.4 emu mol−1. The giant electric field–controlled magnetism was due to the Pna21/R3c field–induced transition, which was confirmed by both structure analysis and theoretical calculation, and the change of remanent magnetization under an electric field was achieved up to 44.8 emu mol−1 (57.9%), which was much bigger than that of rare‐earth (RE)‐substituted BiFeO3 ceramics without optimizing Pna21 phase fraction. The present results might significantly deepen the physical understanding of Pna21 phase and subsequently provide new hints on further enhancing electric field–controlled magnetism in RE‐substituted BiFeO3 multiferroic ceramics. [ABSTRACT FROM AUTHOR]

Rewritable nanoelectronics offer new perspectives and potential to both fundamental research and technological applications. Such interest has driven the research focus into conducting domain walls: pseudo‐2D conducting channels that can be created, positioned, and deleted in situ. However, the study of conductive domain walls is largely limited to wide‐gap ferroelectrics, where the conductivity typically arises from changes in charge carrier density, due to screening charge accumulation at polar discontinuities. This work shows that, in narrow‐gap correlated insulators with strong charge‐lattice coupling, local strain gradients can drive enhanced conductivity at the domain walls—removing polar‐discontinuities as a criteria for conductivity. By combining different scanning probe microscopy techniques, it is demonstrated that the domain wall conductivity in GaV4S8 does not follow the established screening charge model but likely arises from the large surface reconstruction across the Jahn–Teller transition and the associated strain gradients across the domain walls. This mechanism could turn any structural, or even magnetic, domain wall conducting, if the electronic structure of the host is susceptible to local strain gradients—drastically expanding the range of materials and phenomena that may be applicable to domain wall‐based nanoelectronics. [ABSTRACT FROM AUTHOR]

Monophasic GdCrO3 nanoparticles have been fabricated by ethylene glycol‐assisted metal citrate precursor method. The as‐prepared nanoparticles have been characterized for phase purity, size and morphology by using powder X‐ray diffraction, transmission electron microscopy and scanning electron microscopic techniques. GdCrO3 nanoparticles showed excellent crystallinity with an average particle size of 78 nm and high specific surface area of 184 m2 g−1. The two band gap values of 1.9 eV and 2.3 eV were calculated using K−M function of the UV‐visible diffuse reflectance spectroscopy. Magnetic results of GdCrO3 nanoparticles possess the well defined ferromagnetic loop, which confirms the ferromagnetic characteristics of these nanoparticles. Our results further exhibit improved P−E loop for GdCrO3 nanoparticles showing ferroelectric behaviour at room temperature for the first time which indicates the presence of multiferroic nature. The dielectric constant and dielectric loss of sintered/unsintered pellet of GdCrO3 were measured as a function of frequency and temperature. Lastly, the humidity sensing parameters of GdCrO3 nanoparticles have also been reported. [ABSTRACT FROM AUTHOR]

Organic–inorganic hybrid perovskites (OIHPs) have gained tremendous interest for their rich functional properties. However, the coexistence of more than one of ferroelectricity, ferromagnetism and ferroelasticity has been rarely found in OIHPs. Herein, we report a two‐dimensional Cr2+‐based OIHP, [3,3‐difluorocyclobutylammonium]2CrCl4 ([DFCBA]2CrCl4), which shows both ferroelectricity and ferromagnetism. It undergoes a 4/mmmFm type ferroelectric phase transition at a temperature as high as 387 K and shows multiaxial ferroelectricity with a saturate polarization of 2.1 μC cm−2. It acts as a soft ferromagnet with a Curie temperature of 32.6 K. This work throws light on the exploration of OIHPs with the coexistence of ferroelectricity and ferromagnetism for applications in future multifunctional smart devices. [ABSTRACT FROM AUTHOR]

Cyanido‐bridged dimetallic complexes are attracting attention due to their varied structures and properties. However, homochiral cyanido‐bridged dimetallic complexes are rare, and making them ferroelectric is a great challenge. Introducing C−F⋅⋅⋅K interactions between the guest chiral cations and the host [KFe(CN)6]2− framework, gives three‐dimensional cyanido‐bridged dimetallic multiferroics, [R‐ and S‐3‐fluoropyrrolidinium]2[KFe(CN)6] (R‐ and S‐3‐FPC). The mirror‐symmetric vibrational circular dichroism (VCD) signal shows their enantiomeric nature. R‐ and S‐3‐FPC crystallize in the same chiral‐polar space group P21 at 298 K. Piezoresponse force microscopy (PFM), polarizing optical microscopy, and temperature‐dependent second‐harmonic generation (SHG) measurements show their multiferroic properties (the coexistence of ferroelectricity and ferroelasticity), in line with the Aizu notation of 222F2. R‐3‐FPC shows excellent ferroelectricity with saturated polarization up to 9.4 μC cm−2. [ABSTRACT FROM AUTHOR]

In this work, a novel multiferroic‐like nanocomposite is designed and obtained using the high‐pressure torsion (HPT) method. The crystal structure, phase composition, morphology, ferromagnetic (FM), and ferroelectric (FE) properties of the initial powders and ferroelectric/ferromagnetic nanocomposites are studied comprehensively. The initial powders and their composite show the perovskite and spinel crystalline phases for the FE and FM fractions, respectively. After HPT, the particle sizes of the initial powders are decreased significantly. It is shown that the novel nanocomposite consists of exchange‐interacting FE and FM phases and demonstrates improved magnetic and electrical properties in low fields at room temperature. A giant increase in residual polarization with an increase in external high‐pressure is found in new composite. The obtained results make it possible to consider the novel nanocomposite as a new functional material for its use both in electronic devices for monitoring ultra‐high‐pressure and in integrated circuits of high‐speed computing nanosystems with low switching energy. The HPT method is a promising method for obtaining new heterophase nanosystems. [ABSTRACT FROM AUTHOR]

The structural phase transitions in multiferroic TbFe3(BO3)4 with change hydrostatic pressures and temperatures have been studied by Raman spectroscopy and calculation within density functional theory. Lattice dynamics calculations in the TbFe3(BO3)4 crystal in the R32 phase under various values of applied hydrostatic pressure (from 0 up to 5 GPa with 1 GPa step) were performed. The calculation performed in this work in a TbFe3(BO3)4 crystal showed that the applied pressure can increase the phase transition temperature. Raman spectra of the TbFe3(BO3)4 crystal have been investigated at simultaneously high temperature and high pressure (up to 5.14 GPa and 465 K). The appearance of a soft mode was observed with decreasing temperature at normal pressure. The manifestations of the interaction of the structural and magnetic order parameters in the range from 13 to 50 K were observed at normal pressure. With increasing pressure and a fixed temperature, recovery of the soft modes is also observed. The experimental p–T phase diagram of TbFe3(BO3)4 was established. An increase in pressure leads to an increase in the temperature of transition. [ABSTRACT FROM AUTHOR]

One of the key concepts in flexible/freestanding spintronics is the effective control of ultra‐thin film magnetism, and at the same time assures that the functional properties will not be compromised when gating methods are applied. Traditionally, strain application is through magnetoelectric effect while using the gate voltage to transfer the strain to the magnetism layer, which can lead the noise in the heterostructure. On the other hand, the knowledge of freestanding magnetism changes largely lacks quantitative analysis. Coupling the freestanding characteristic such as large strain with important magnetic properties can further expand the freestanding spintronics storage area. In this work, the high‐quality freestanding multiferroic heterostructures of SrTiO3(001)/Sr3Al2O6/BaTiO3/Ta/(Co/Pt)5 with different Co thicknesses have been successfully prepared with both pulsed laser deposition and magnetism sputtering processes. The ultra‐flexible freestanding structure shows a strong strain gating effect with bending, that the ferromagnetic resonance (FMR) shifts around 440 Oe at room temperature with tensile strain. Upon decreasing the temperature to BaTiO3 phase transition range from T‐phase to O‐phase and O‐phase to R‐phase, respectively, a sharp FMR shift can be observed for both in‐plane and out‐of‐plane measurements. This work suggests that the tunable flexible spintronics are achievable through freestanding mechanisms and shows the promising future of freestanding spintronics. [ABSTRACT FROM AUTHOR]

In improper ferroelectrics, the spontaneous ordering is typically driven by a structural distortion or a magnetic spin alignment. The induced electric polarization is only a secondary effect. This dependence is a rich source for unusual phenomena and ferroelectric domain configurations for proper, polarization‐driven ferroelectrics. This study focuses on the polar domain structure and the hysteretic behavior at the ferroelectric phase transition in Ca3Mn1.9Ti0.1O7 as a representative of the recently discovered hybrid improper ferroelectric class of multiferroics. Combining optical second harmonic generation and Raman spectroscopy gives access to the spontaneous structural distortion and the resulting improper electric polarization. This study shows that hybrid improper ferroelectrics contrast proper and improper ferroelectrics in several ways. Most intriguingly, adjacent ferroelectric domains favor head‐to‐head and tail‐to‐tail domain walls over charge‐neutral configurations. Furthermore, the phase transition occurs in an asymmetric fashion. The regime of phase coexistence of the nonpolar and polar phases shows a clear and abrupt upper temperature limit. In contrast, the coexistence toward low temperatures is best described as a fade‐out process, where 100‐nm‐sized islands of the nonpolar phase expand deep into the polar phase. [ABSTRACT FROM AUTHOR]

Thin films of bismuth and iron oxides were obtained by atomic layer deposition (ALD) on the surface of a flexible substrate poly(4,4′‐oxydiphenylene‐pyromellitimide) (Kapton) at a temperature of 250°C. The layer thickness was 50 nm. The samples were examined by secondary‐ion mass spectrometry, and uniform distribution of elements in the film layer was observed. Surface morphology, electrical polarization, and mechanical properties were investigated by atomic force microscope, piezoelectric force microscopy, and force modulation microscopy. The values of current in the near‐surface layer varied in the range of ±80 pA when a potential of 5 V was applied. Chemical analysis was performed by X‐ray photoelectron spectroscopy, where the formation of Bi2O3 and Fe2O3 phases, as well as intermediate phases in the Bi–Fe–O system, was observed. Magnetic measurements were carried out by a vibrating sample magnetometer that showed a ferromagnetic response. The low‐temperature method of functionalization of the Kapton surface with bismuth and iron oxides will make it possible to adapt the Bi–Fe–O system to flexible electronics. [ABSTRACT FROM AUTHOR]

Neodymium iron borate NdFe3(BO3)4 is an intensively studied multiferroic with high electric polarization values controlled by a magnetic field. It is characterized by a large quadratic magnetoelectric effect, rigidity in the base plane and a rather strong piezoelectric effect. In this work, the atomic structure of (Nd0.91Bi0.09)Fe3(BO3)4 was studied by single‐crystal X‐ray diffraction in the temperature range 20–500 K (space group R32, Z = 3). The Bi atoms found in the composition partially substitute the Nd atoms in the 3a position; they entered the structure due to the growth conditions in the presence of Bi2Mo3O12. It was shown that in the temperature range 20–500 K there is no structural phase transition R32→P3121, which occurs in rare‐earth iron borates (RE = Eu–Er, Y) with an effective rare‐earth cation radius smaller than that of Nd. The temperature dependence of the unit‐cell c parameter reveals a slight increase on cooling below 90 K, which is similar to the results obtained previously for iron borates of Gd, Y and Ho. The atomic distances (Nd,Bi)—O, (Nd,Bi)—B, (Nd,Bi)—Fe, Fe—O, Fe—B and Fe—Fe in the iron chains and between chains decrease steadily with decreasing temperature from 500 to 90 K, whereas the B1(3b)—O distance does not change and the average B2(9e)—O distance increases slightly. There is a uniform decrease in the atomic displacement parameters with decreasing temperature, with a more pronounced decrease for the Nd(3a) and O2(9e) atoms. The O2(9e) atoms are characterized by the maximum atomic displacement parameters and the most elongated atomic displacement ellipsoids. The characteristic Debye and Einstein temperatures, and the static component in the atomic displacements were determined for cations using multi‐temperature diffraction data. It was shown that the Nd cations have the weakest bonds with the surrounding atoms and the B cations have the strongest. [ABSTRACT FROM AUTHOR]

As a promising candidate for the much‐desired low power consumption spintronic devices, 2D magnetic van der Waals material also provides a versatile platform for the design and control of topological spin textures. In this work on WTe2/CrCl3 bilayer van der Waals heterostructures, a complete Néel‐type skyrmion–bimeron–ferromagnet phase transition is demonstrated, accompanied by the evolution of the topological number. This cyclic transition, mediated by a perpendicular magnetic field, is largely driven by the competition between the out‐of‐plane magnetocrystalline anisotropy and magnetic dipole–dipole interaction. In the presence of a driving current, the Néel‐type skyrmion gains a higher velocity yet larger skyrmion Hall angle, in comparison to the bimeron. By incorporating a ferroelectric CuInP2S6 monolayer as a substrate, writing and erasing of skyrmions may be regulated using a ferroelectric polarization. This work sheds light on a novel approach to the design and control of magnetic skyrmions on 2D van der Waals materials. [ABSTRACT FROM AUTHOR]

Magnetic structure of the Co ions in monoclinic Co3TeO6 in the antiferroelectric state at 16 K has been determined by neutron powder together with single‐crystal diffractions. The indices of the magnetic reflections that appear at the incommensurate positions were determined by diffractions from a single crystal, which allow to uniquely identify the magnetic modulation vector. There are two crystallographically distinct Co layers. Magnetic incommensurability appears in the Co spins in the layers comprising zig‐zag chains, with a magnetic modulation vector of (0.357, 0.103, 0.121) at 3 K but changes to (0.4439, 0, 0.137) at 16 K, while the Co ions in the honeycomb webs form a collinear antiferromagnetic structure. Thermal reduction rate of the Co moments in the honeycomb webs was found to be much smaller than those in the zig‐zag chains. Shifting of large amounts of electronic charge into the CoO bonds in the honeycomb webs on warming is used to understand the behavior. [ABSTRACT FROM AUTHOR]

Magnetic structure of the Co ions in monoclinic Co3TeO6 in the antiferroelectric state at 16 K has been determined by neutron powder together with single‐crystal diffractions. The indices of the magnetic reflections that appear at the incommensurate positions were determined by diffractions from a single crystal, which allow to uniquely identify the magnetic modulation vector. There are two crystallographically distinct Co layers. Magnetic incommensurability appears in the Co spins in the layers comprising zig‐zag chains, with a magnetic modulation vector of (0.357, 0.103, 0.121) at 3 K but changes to (0.4439, 0, 0.137) at 16 K, while the Co ions in the honeycomb webs form a collinear antiferromagnetic structure. Thermal reduction rate of the Co moments in the honeycomb webs was found to be much smaller than those in the zig‐zag chains. Shifting of large amounts of electronic charge into the CoO bonds in the honeycomb webs on warming is used to understand the behavior. [ABSTRACT FROM AUTHOR]

The explosive expansion of multiferroics literature in recent years demonstrates the fast‐growing interest in this field. Although bismuth ferrite is one of the most extensively investigated multiferroic compounds combining magnetoelectric, i.e., antiferromagnetic and ferroelectric features at room temperature, the challenge of producing single‐phase particles remains because the role of multiple synthetic parameters must be unraveled. Herein, the facile synthetic route of aqueous coprecipitation is selected as the first synthetic step, followed by a 700 °C annealing stage to synthesize bismuth ferrite nanoparticles (NPs). This article aims to clarify the influence of ingredients such as precursors: base solution, acid and the Bi/Fe molar ratio, and the role of synthetic parameters such as pH level and reaction temperature toward higher yields of purer crystalline phases. Both structural and magnetic features' performance outline the significance of both stages on forming BiFeO3 single‐phase NPs with the absence of any secondary bismuth oxide phases, a crucial issue for multiferroic features at room temperature. [ABSTRACT FROM AUTHOR]

The pure and Mn‐doped BiFe1−xMnxO3 (x = 0.00, 0.02, 0.05, 0.10) nanomaterials have been prepared by coprecipitation method. The powder X‐ray diffraction pattern analysis shows a structural phase transformation from rhombohedral to orthorhombic, as Mn content in the doped BiFe1−xMnxO3 increases from x = 0.00 to 0.10. The Raman spectrum analysis of BiFe1−xMnxO3 also confirms structural phase transformation. The average crystallite size was calculated using the Scherrer formula and found to decrease from 100 to 60 nm. The surface structure of interconnecting cubic grain turns into spherical grains via petal‐shaped grains with increasing the Mn‐doping concentration. The value of dielectric constant at the frequency of 1 MHz increases rapidly from 27.2 to 76.8 whereas the tangent loss (tan δ) increases gradually from 0.26 to 0.55 as the Mn‐doping concentration increases from x = 0.00 to 0.10. It reveals the enhancement of ferroelectric behavior and suppression of the leakage current density. The drastic change in the phase image contrast of magnetic force micrographs with increasing Mn‐doping concentration in BiFe1−xMnxO3 also indicates the improvement of the ferromagnetism. [ABSTRACT FROM AUTHOR]

A band‐stop filter with dual resonators of yttrium iron garnet (YIG) and lead zirconate titanate (PZT) operating in the S‐ and C‐bands was designed and characterized. Such multiferroic composite resonators allow for mechanical strain mediated control of the ferromagnetic resonance frequency of YIG via a DC voltage applied to PZT. The electric field E‐tuning of the central frequency of the individual resonators by 65‐70 MHz has been utilized for the control of the isolation characteristics by 17 dB and to achieve a maximum transmission loss of 37 dB. The 3 dB‐width of the stop‐band can also be tuned between 40 and 100% when a DC voltage is applied to only one of the two resonators. Such E‐tuning of filter characteristics are of interest for applications in communication systems. [ABSTRACT FROM AUTHOR]

The multiferroic magnetoelectric composites have attracted great interest due to some new expected physics and wide practical applications. However, the low resistivity restricts their further applications. In this work, multiferroic 0.8BaTiO3-0.2BaFe12- xMn xO19 composite ceramics were prepared by microwave-hydrothermal and microwave-sintering methods. It was found that the dielectric constant of the composites increased with increasing x, while the resistivity increased gradually. Accordingly, the dielectric loss dropped as expected and the P-E loops showed slimmer shapes after introducing of Mn ions. In addition, the magnetic hysteresis loops of the composite ceramics prepared showed an excellent ferromagnetic behavior. In summary, smaller leakage current and slim P-E loops were obtained through Mn ion doping in BaFe12O19 and forming BaTiO3-BaFe12− xMn xO19 composite ceramics while maintaining their good ferromagnetic property successfully. [ABSTRACT FROM AUTHOR]

Bismuth ferrite (BiFeO3) materials have been the subject of intense research activity in the last two decades. The great interest arises from the BiFeO3 being one of the rare multiferroic compounds in which ferroelectricity and magnetism coexist at room temperature. To improve these properties several studies have been reported on the doping at the A and/or B sites of the BiFeO3 perovskite structure. In this short review, the attention is focused to the synthesis of BiFeO3 and BiFeO3 doped with Ba or Dy at the A site and Ti at the B site through Metal Organic Chemical Vapor Deposition (MOCVD). The applied MOCVD process consists of an in situ one step approach using a multi-metal source precursor mixture containing the Bi(phenyl)3 and Fe(tmhd)3 (phenyl = -C6H5; H-tmhd = 2,2,6,6-tetramethyl-3,5-heptandione) as source of Bi and Fe ions. This study evidences the effect of doping on the structural, morphological and piezo/ferroelectric properties of BiFeO3 and doped systems. In summary, this mini-review illustrates the possibility to apply a simple MOCVD approach to produce good quality pure and doped BiFeO3 films. [ABSTRACT FROM AUTHOR]

Magnetoelectric barium titanate ceramics with embedded cobalt iron alloy particles (Co1/3Fe2/3) x-(BaTiO3)(1− x), with x=0.2, 0.4, and 0.6, were prepared by a polyol-mediated synthesis with subsequent sintering in a reducing forming gas atmosphere. The samples were characterized by XRD and SEM/ EDX measurements. The sizes of the Co1/3Fe2/3 grains increase with x. Impedance spectroscopy showed a behavior similar to pure BaTiO3, in particular the occurrence of the ferroelectric-paraelectric phase transition, and high permittivities for the sample with x=0.6, that is, near the percolation threshold. The samples exhibit soft ferromagnetic properties with large saturation magnetizations of 2.5 μB/atom and narrow hystereses. Detailed magnetoelectric investigations revealed a unique DC-field dependence of α ME for all three compositions. Most remarkably, the sample with x=0.4 possesses a broad ME hysteresis and an inversion of the sign of α ME at 5 kOe. [ABSTRACT FROM AUTHOR]

Ferromagnetic resonance (FMR) is one of the most important characteristics of soft magnetic materials, which practically sets the maximum operation speed of these materials. There are two FMR modes in exchange coupled ferromagnet/nonmagnet/ferromagnet sandwich films. The acoustic mode has relatively lower frequency and is widely used in radio-frequency/microwave devices, while the optical mode is largely neglected due to its tiny permeability even though it supports much higher frequency. Here, a realistic method is reported to enhance the permeability in the optical mode to an applicable level. FeCoB/Ru/FeCoB trilayers are carefully engineered with both uniaxial magnetic anisotropy and antiferromagnetic interlayer exchange coupling. This special magnetic structure exhibits a high optical mode frequency up to 11.28 GHz and a maximum permeability of 200 at resonance. An abnormally low inverse switch field (<200 Oe, less than 1/5 of the single layer) is observed which can effectively switch the system from optical mode with higher frequency into acoustic mode with lower frequency. The optical mode frequency and inverse switch field can be controlled by tailoring the interlayer coupling strengths and the uniaxial anisotropy fields, respectively. The tunable optical mode resonance thus can increase operation frequency while reduce operation field overhead in FMR based devices. [ABSTRACT FROM AUTHOR]

BiFeO3 epitaxial thin films fabricated by pulsed laser deposition on different scandate substrates were investigated by means of Raman spectroscopy. We observed periodic changes in Raman position, full width at half maximum and intensity for some phonon modes as a function of the azimuthal angle . Further analysis revealed the possibility to assign the so far controversial discussed Raman modes at low wavenumbers (<250 cm-1) through rotational Raman measurements at different azimuthal angles, which show high sensitivity to the aforementioned parameters. Furthermore, the ferroelectric/ferroelastic domain structure shown by piezo-response force microscopy investigations of the samples was confirmed. Our results are supported by symmetry-based cal- culations including the analysis of Raman scattering geometry as well as the dielectric function of BiFeO3 in the infrared range. [ABSTRACT FROM AUTHOR]

We report the effects of elemental substitutions in multiferroic R Fe2O4 ( R: Y, Ho-Lu, In). The substitution by nonmagnetic Ga3+ at the Fe site, which has not been reported so far, shows a drastic decrease in the ferrimagnetic transition temperature ( TN). This is plausibly owing to the suppression of magnetic interactions between Fe ions, based on our previous results of other substituted systems such as R FeCoO4. Dielectric constants near room temperature were comparable to those of R Fe2O4. The suppression of dielectric loss in this system is suitable to application. The R -site substitution was also attempted by the large R3+ ions such as Dy3+. The solubility limit was up to ∼10% of R ions. TN was raised by 5-10 K for Dy3+ substitution. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

A Cu-based organic-inorganic perovskite framework exhibits high-temperature ferroelectricity with strong magnetoelectric effects. Both electric field control of magnetization and magnetic field control of polarization are realized. Theoretical calculations suggest that a new mechanism of hybrid improper ferroelectricity arising from the Jahn-Teller distortions of magnetic metal ions and tilting of the organic cations are responsible for the peculiar multiferroic behaviors. [ABSTRACT FROM AUTHOR]

Highly strained films of BiFe0.5Mn0.5O3 (BFMO) grown at very low rates by pulsed laser deposition were demonstrated to exhibit both ferrimagnetism and ferroelectricity at room temperature and above. Magnetisation measurements demonstrated ferrimagnetism ( TC ∼ 600K), with a room temperature saturation moment ( MS) of up to 90 emu/cc (∼ 0.58 μB/f.u) on high quality (001) SrTiO3. X-ray magnetic circular dichroism showed that the ferrimagnetism arose from antiferromagnetically coupled Fe3+ and Mn3+. While scanning transmission electron microscope studies showed there was no long range ordering of Fe and Mn, the magnetic properties were found to be strongly dependent on the strain state in the films. The magnetism is explained to arise from one of three possible mechanisms with Bi polarization playing a key role. A signature of room temperature ferroelectricity in the films was measured by piezoresponse force microscopy and was confirmed using angular dark field scanning transmission electron microscopy. The demonstration of strain induced, high temperature multiferroism is a promising development for future spintronic and memory applications at room temperature and above. [ABSTRACT FROM AUTHOR]

Highly strained films of BiFe0.5Mn0.5O3 (BFMO) grown at very low rates by pulsed laser deposition were demonstrated to exhibit both ferrimagnetism and ferroelectricity at room temperature and above. Magnetisation measurements demonstrated ferrimagnetism ( TC ∼ 600K), with a room temperature saturation moment ( MS) of up to 90 emu/cc (∼ 0.58 μB/f.u) on high quality (001) SrTiO3. X-ray magnetic circular dichroism showed that the ferrimagnetism arose from antiferromagnetically coupled Fe3+ and Mn3+. While scanning transmission electron microscope studies showed there was no long range ordering of Fe and Mn, the magnetic properties were found to be strongly dependent on the strain state in the films. The magnetism is explained to arise from one of three possible mechanisms with Bi polarization playing a key role. A signature of room temperature ferroelectricity in the films was measured by piezoresponse force microscopy and was confirmed using angular dark field scanning transmission electron microscopy. The demonstration of strain induced, high temperature multiferroism is a promising development for future spintronic and memory applications at room temperature and above. [ABSTRACT FROM AUTHOR]

The multiferroic Pb(Fe1/2V1/2)O3 (PFV) bulk ceramic was fabricated by a conventional ceramic sintering method. The strong visible-light photovoltaic effect in Sn-doped-In2O3(ITO)/PFV/ITO structure capacitor was observed. The open-circuit voltage was up to ∼0.7 V, which was much higher than the value (∼0.3 V) in BiFeO3 film. The photo-excited electric current is almost proportional to the incident light illumination intensity. The good visible-light photovoltaic makes PFV ceramic a potential candidate for practical application in solar cell devices. [ABSTRACT FROM AUTHOR]

Polymer-based magnetoelectric (ME) materials are an interesting, challenging and innovative research field, that will bridge the gap between fundamental research and applications in the near future. Here, the current state of the art on the different materials, the used configurations for the development of sensors and actuators, as well as the main values of the ME coupling obtained for the different polymer-based systems are summarized. Further, some of the specific applications that are being developed for those polymer-based ME materials are addressed as well as the main advantages and remaining challenges in this research field. [ABSTRACT FROM AUTHOR]

The available data on the structural and magnetic transitions in multiferroic hexagonal YMnO3 have been reviewed, first making use of the computer programs from the group theoretical ISOTROPY software suite to list possible crystal and magnetic structures, then taking into account the capability of neutron diffraction and other physical methods to distinguish them. This leads to a clear view of the transformation sequence, as follows. Hexagonal YMnO3 is paraelectric in P63/ mmc at elevated temperatures, and undergoes a single structural transition on cooling through 1250 K to a ferrielectric phase in P63 cm that is retained through room temperature. At a much lower temperature, 70 K, there is a magnetic transition from paramagnetic to a triangular antiferromagnetic arrangement, most likely with symmetry P63′ cm′. Comment is made on the unusual coupling of ferroelectric and magnetic domains reported to occur in this material, as well as on the so-called `giant magneto-elastic' effect. [ABSTRACT FROM AUTHOR]

The available data on the structural and magnetic transitions in multiferroic hexagonal YMnO3 have been reviewed, first making use of the computer programs from the group theoretical ISOTROPY software suite to list possible crystal and magnetic structures, then taking into account the capability of neutron diffraction and other physical methods to distinguish them. This leads to a clear view of the transformation sequence, as follows. Hexagonal YMnO3 is paraelectric in P63/ mmc at elevated temperatures, and undergoes a single structural transition on cooling through 1250 K to a ferrielectric phase in P63 cm that is retained through room temperature. At a much lower temperature, 70 K, there is a magnetic transition from paramagnetic to a triangular antiferromagnetic arrangement, most likely with symmetry P63′ cm′. Comment is made on the unusual coupling of ferroelectric and magnetic domains reported to occur in this material, as well as on the so-called `giant magneto-elastic' effect. [ABSTRACT FROM AUTHOR]

The aim of this work is to fabricate an all-oxide spin valve using multiferroic BiFeO3 as the antiferromagnetic pinning layer, in the hope that we may be able to switch magnetoresistance electrically. The proposed architecture is Zn0.7Ni0.3Fe2O4/ Sr1- xLa xTiO3/ Zn0.7Ni0.3Fe2O4/ BiFeO3/ LaNiO3/SrTiO3. We have demonstrated that such a multilayer structure can be grown epitaxially by the RF magnetron sputtering. X-ray diffraction showed that the films were indeed biaxially aligned with reasonable in-plane and out-of-plane textures, under the growth conditions optimised for achieving good ferroelectric and magnetic properties. X-ray photoelectron spectroscopy depth profiling showed that there was significant Bi diffusion across the interface if the BiFeO3 film was not stabilised in high oxygen ambience after deposition. High-resolution transmission electron microscopy showed a tidy and sharp Zn0.7Ni0.3Fe2O4/ BiFeO3 boundary for the Zn0.7Ni0.3Fe2O4 films grown at 550 °C, while for the films grown at higher temperature an irregular interface was observed. Under the optimum growth condition, a clear exchange bias was achieved at the Zn0.7Ni0.3Fe2O4/ BiFeO3 interface. [ABSTRACT FROM AUTHOR]

The aim of this work is to fabricate an all-oxide spin valve using multiferroic BiFeO3 as the antiferromagnetic pinning layer, in the hope that we may be able to switch magnetoresistance electrically. The proposed architecture is Zn0.7Ni0.3Fe2O4/ Sr1- xLa xTiO3/ Zn0.7Ni0.3Fe2O4/ BiFeO3/ LaNiO3/SrTiO3. We have demonstrated that such a multilayer structure can be grown epitaxially by the RF magnetron sputtering. X-ray diffraction showed that the films were indeed biaxially aligned with reasonable in-plane and out-of-plane textures, under the growth conditions optimised for achieving good ferroelectric and magnetic properties. X-ray photoelectron spectroscopy depth profiling showed that there was significant Bi diffusion across the interface if the BiFeO3 film was not stabilised in high oxygen ambience after deposition. High-resolution transmission electron microscopy showed a tidy and sharp Zn0.7Ni0.3Fe2O4/ BiFeO3 boundary for the Zn0.7Ni0.3Fe2O4 films grown at 550 °C, while for the films grown at higher temperature an irregular interface was observed. Under the optimum growth condition, a clear exchange bias was achieved at the Zn0.7Ni0.3Fe2O4/ BiFeO3 interface. [ABSTRACT FROM AUTHOR]

The modulated crystal structure and modulated magnetic ordering of the multiferroic CaCu xMn7− xO12 is studied by analysing neutron and synchrotron-radiation (SR) powder diffraction data with a model based on the magnetic superspace group R31′(00γ) ts. Both atomic position modulations and magnetic modulations are described with the modulation vector (0, 0, q). The magnetic ordering is a screw-type circular helix where the magnetic moments are perpendicular to the c direction. The temperature dependence of the modulation vector length and the ordered magnetic moments of Mn3+ and Mn4+ ions is given between T = 50 K and the Néel temperature TN≃ 90 K. The atomic position modulation length Lp and the magnetic modulation length Lm fulfil the relation Lm = 2 Lp at all temperatures between 50 K and TN. [ABSTRACT FROM AUTHOR]

Neodymium iron borate NdFe 3 (BO 3 ) 4 is an intensively studied multiferroic with high electric polarization values controlled by a magnetic field. It is characterized by a large quadratic magnetoelectric effect, rigidity in the base plane and a rather strong piezoelectric effect. In this work, the atomic structure of (Nd 0.91 Bi 0.09 )Fe 3 (BO 3 ) 4 was studied by single-crystal X-ray diffraction in the temperature range 20-500 K (space group R32, Z = 3). The Bi atoms found in the composition partially substitute the Nd atoms in the 3a position; they entered the structure due to the growth conditions in the presence of Bi 2 Mo 3 O 12 . It was shown that in the temperature range 20-500 K there is no structural phase transition R32→P3 1 21, which occurs in rare-earth iron borates (RE = Eu-Er, Y) with an effective rare-earth cation radius smaller than that of Nd. The temperature dependence of the unit-cell c parameter reveals a slight increase on cooling below 90 K, which is similar to the results obtained previously for iron borates of Gd, Y and Ho. The atomic distances (Nd,Bi)-O, (Nd,Bi)-B, (Nd,Bi)-Fe, Fe-O, Fe-B and Fe-Fe in the iron chains and between chains decrease steadily with decreasing temperature from 500 to 90 K, whereas the B1(3b)-O distance does not change and the average B2(9e)-O distance increases slightly. There is a uniform decrease in the atomic displacement parameters with decreasing temperature, with a more pronounced decrease for the Nd(3a) and O2(9e) atoms. The O2(9e) atoms are characterized by the maximum atomic displacement parameters and the most elongated atomic displacement ellipsoids. The characteristic Debye and Einstein temperatures, and the static component in the atomic displacements were determined for cations using multi-temperature diffraction data. It was shown that the Nd cations have the weakest bonds with the surrounding atoms and the B cations have the strongest.

Magnetic metal–organic frameworks (MOFs) with a perovskite structure AMX3 are emerging single‐phased multiferroics with different sources of magnetic and electric ordering. However, the atomic mechanism underlying the multiple ferroic coupling is convincingly clarified. In this work, large single crystals of [(CH3)2NH2][Ni(HCOO)3] are synthesized and shown to exhibit a first‐order ferroelectric phase transition at ≈178 K during heating and at ≈151 K during cooling, as confirmed by temperature‐dependent differential scanning calorimetry, Raman scattering, and X‐ray diffraction studies. Resonant ultrasound spectroscopy (RUS) is used to investigate the elastic and anelastic properties between 5 and 300 K. The RUS results show an abrupt disappearance of resonance peaks above the ferroelectric transition point of ≈178 K. This is probably due to the unfreezing of dimethylammonium cation motion which couples with local strain. Small changes in elastic properties associated with two known magnetic transition at ≈35 and ≈15 K, respectively, are indicative of weak magnetoelastic coupling. An apparent peak in acoustic loss accompanying the canted antiferromagnetic ordering (≈35 K) and spin reorientation transition (≈15 K) is attributed to dynamical magnetoelastic coupling on the RUS time scale of ≈10−6 s. In comparison with the same MOF structures containing Mn2+ and Co2+, the smaller Ni2+ ions effectively generate an internal chemical pressure and induce a compressed ion force on the anion frameworks. This study opens up a new landscape to explore possibilities for ferroic‐order coupling in molecular MOFs. A type‐I multiferroic phase of [(CH3)2NH2][Ni(HCOO)3] creates significant elastic and anelastic anomalies associated with the ferroelectric and magnetic ordering transition. The overlapping strains, from separated ferroic ordering parameters, could provide a mechanism for strong magnetoelectric properties in nickel‐based molecular multiferroics. [ABSTRACT FROM AUTHOR]

The available data on the structural and magnetic transitions in multiferroic hexagonal YMnO3 have been reviewed, first making use of the computer programs from the group theoretical ISOTROPY software suite to list possible crystal and magnetic structures, then taking into account the capability of neutron diffraction and other physical methods to distinguish them. This leads to a clear view of the transformation sequence, as follows. Hexagonal YMnO3 is paraelectric in P63/mmc at elevated temperatures, and undergoes a single structural transition on cooling through 1250 K to a ferrielectric phase in P63cm that is retained through room temperature. At a much lower temperature, 70 K, there is a magnetic transition from paramagnetic to a triangular antiferromagnetic arrangement, most likely with symmetry P63'cm'. Comment is made on the unusual coupling of ferroelectric and magnetic domains reported to occur in this material, as well as on the so-called `giant magneto-elastic' effect.