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One of the most innovative possibilities offered by oxides is the use of heat currents for computational purposes. Towards this goal, phase-change oxides, including ferroelectrics, ferromagnets and related materials, could reproduce sources, logic units and memories used in current and future computing schemes.

Heterovalent doped (K0.48-0.07xNa0.52-0.43xBi0.5x)(Nb0.95-0.95xSb0.05-0.05xZrx)O3 ceramics were fabricated using conventional solid-state reaction. Then, the phase structures, dielectric, ferroelectric, and electric-strain properties were investigated. The compositions were tuned to be located at polymorphic phase boundary with increasing heterovalent Bi3+ and Zr4+ doping levels. A large strain of 0.19% was obtained at relatively low electric fields of 30 kV/cm in the composition of x = 0.04. The normalized large-signal d33* values were approximately 633 pm/V under a low driving electric field of 30 kV/cm, which were comparable or larger than the values reported for other lead-free families. The large strains obtained can be attributed to the formation of nanodomains and high-density domain walls, which were confirmed by the observations of domain morphology using transmission electron microscopy (TEM) technique. Excellent temperature stability of the strain properties of the x = 0.04 sample could be ascribed to the sluggish behaviour for the local structural heterogeneity in heterovalent-ion doped KNN ceramic. Theoretical simulations revealed that the Zr4+ produce the local stress at the BO6 octahedra and Bi3+ could yield off-centering of AO12 ployhedron due to the nature of Bi 6s lone pair electrons, which induced lattice expansion and local distortions in the sample. The local displacements are strongly anisotropic in heterovalent-ion doped system. It is believed that random local fields exist in these compositions owing to the eixstence of charge distribution. Such heterovalent doping of Bi3+ and Zr4+ could destory simutiously the orthorhombic symmetry and the short-range ferroelecctric order, leading to the formation of complex nanodomains and local structral hetergenenity. Heterovalent doping may, therefore, offer a new avenve to design novel K0.5Na0.5NbO3 (KNN) -based materials for their mutifunctional applications., Funder: National Science Foundation of China (grant no. 52172125); the CSS project (grant no. YK2015-0602006); Natural Science Foundation of Shandong Province of China (grant no. ZR2018BA028); Quzhou Science and Technology Plan Project (grant no. 2022K108); General Research Project of Zhejiang Provincial De-partment of Education (grant no. Y202249978)

Heterovalent doped (K0.48-0.07xNa0.52-0.43xBi0.5x)(Nb0.95-0.95xSb0.05-0.05xZrx)O3 ceramics were fabricated using conventional solid-state reaction. Then, the phase structures, dielectric, ferroelectric, and electric-strain properties were investigated. The compositions were tuned to be located at polymorphic phase boundary with increasing heterovalent Bi3+ and Zr4+ doping levels. A large strain of 0.19% was obtained at relatively low electric fields of 30 kV/cm in the composition of x = 0.04. The normalized large-signal d33* values were approximately 633 pm/V under a low driving electric field of 30 kV/cm, which were comparable or larger than the values reported for other lead-free families. The large strains obtained can be attributed to the formation of nanodomains and high-density domain walls, which were confirmed by the observations of domain morphology using transmission electron microscopy (TEM) technique. Excellent temperature stability of the strain properties of the x = 0.04 sample could be ascribed to the sluggish behaviour for the local structural heterogeneity in heterovalent-ion doped KNN ceramic. Theoretical simulations revealed that the Zr4+ produce the local stress at the BO6 octahedra and Bi3+ could yield off-centering of AO12 ployhedron due to the nature of Bi 6s lone pair electrons, which induced lattice expansion and local distortions in the sample. The local displacements are strongly anisotropic in heterovalent-ion doped system. It is believed that random local fields exist in these compositions owing to the eixstence of charge distribution. Such heterovalent doping of Bi3+ and Zr4+ could destory simutiously the orthorhombic symmetry and the short-range ferroelecctric order, leading to the formation of complex nanodomains and local structral hetergenenity. Heterovalent doping may, therefore, offer a new avenve to design novel K0.5Na0.5NbO3 (KNN) -based materials for their mutifunctional applications., Funder: National Science Foundation of China (grant no. 52172125); the CSS project (grant no. YK2015-0602006); Natural Science Foundation of Shandong Province of China (grant no. ZR2018BA028); Quzhou Science and Technology Plan Project (grant no. 2022K108); General Research Project of Zhejiang Provincial De-partment of Education (grant no. Y202249978)

Typically, magnetic phenomena result from the spontaneous order of the sublattices. Here, the cross-talk of two magnetic ions gives rise to an intrinsic, yet non-spontaneous ordering and manifests as emergent strong spin-phonon coupling in SmFeO3. Many material properties such as superconductivity, magnetoresistance or magnetoelectricity emerge from the non-linear interactions of spins and lattice/phonons. Hence, an in-depth understanding of spin-phonon coupling is at the heart of these properties. While most examples deal with one magnetic lattice only, the simultaneous presence of multiple magnetic orderings yield potentially unknown properties. We demonstrate a strong spin-phonon coupling in SmFeO3 that emerges from the interaction of both, iron and samarium spins. We probe this coupling as a remarkably large shift of phonon frequencies and the appearance of new phonons. The spin-phonon coupling is absent for the magnetic ordering of iron alone but emerges with the additional ordering of the samarium spins. Intriguingly, this ordering is not spontaneous but induced by the iron magnetism. Our findings show an emergent phenomenon from the non-linear interaction by multiple orders, which do not need to occur spontaneously. This allows for a conceptually different approach in the search for yet unknown properties.

Organic ferroelectrics are increasingly important due to their complementary properties to classical, inorganic ferroelectrics. Flexibility, chemical resistance, scalability, high breakdown fields, and biocompatibility are attractive for many applications like energy harvesting and storage. The most known energy harvesting methods are piezoelectric, pyroelectric, and triboelectric. Here, we apply the well-established material's figures of merit to five polyvinylidene-fluoride-based compositions ranging from ferroelectric to relaxor-like behavior to emphasize the importance of several key material parameters contributing to the maximal power output of energy harvesting devices. Afterward, we discuss the possibility of the same functional material storing the output energy for the development of scalable multifunctional devices.

Organic ferroelectrics are increasingly important due to their complementary properties to classical, inorganic ferroelectrics. Flexibility, chemical resistance, scalability, high breakdown fields, and biocompatibility are attractive for many applications like energy harvesting and storage. The most known energy harvesting methods are piezoelectric, pyroelectric, and triboelectric. Here, we apply the well-established material's figures of merit to five polyvinylidene-fluoride-based compositions ranging from ferroelectric to relaxor-like behavior to emphasize the importance of several key material parameters contributing to the maximal power output of energy harvesting devices. Afterward, we discuss the possibility of the same functional material storing the output energy for the development of scalable multifunctional devices.

Typically, magnetic phenomena result from the spontaneous order of the sublattices. Here, the cross-talk of two magnetic ions gives rise to an intrinsic, yet non-spontaneous ordering and manifests as emergent strong spin-phonon coupling in SmFeO3. Many material properties such as superconductivity, magnetoresistance or magnetoelectricity emerge from the non-linear interactions of spins and lattice/phonons. Hence, an in-depth understanding of spin-phonon coupling is at the heart of these properties. While most examples deal with one magnetic lattice only, the simultaneous presence of multiple magnetic orderings yield potentially unknown properties. We demonstrate a strong spin-phonon coupling in SmFeO3 that emerges from the interaction of both, iron and samarium spins. We probe this coupling as a remarkably large shift of phonon frequencies and the appearance of new phonons. The spin-phonon coupling is absent for the magnetic ordering of iron alone but emerges with the additional ordering of the samarium spins. Intriguingly, this ordering is not spontaneous but induced by the iron magnetism. Our findings show an emergent phenomenon from the non-linear interaction by multiple orders, which do not need to occur spontaneously. This allows for a conceptually different approach in the search for yet unknown properties.

Organic ferroelectrics are increasingly important due to their complementary properties to classical, inorganic ferroelectrics. Flexibility, chemical resistance, scalability, high breakdown fields, and biocompatibility are attractive for many applications like energy harvesting and storage. The most known energy harvesting methods are piezoelectric, pyroelectric, and triboelectric. Here, we apply the well-established material's figures of merit to five polyvinylidene-fluoride-based compositions ranging from ferroelectric to relaxor-like behavior to emphasize the importance of several key material parameters contributing to the maximal power output of energy harvesting devices. Afterward, we discuss the possibility of the same functional material storing the output energy for the development of scalable multifunctional devices.

The CuxNi1−xFe2O4 (x = 0.0, 0.2, 0.5, 0.8, 1.0) nanoferrite powder were synthesized through chemical co-precipitation method using only (FeCl3, 6H2O), (NiCl2, 6H2O), (CuCl2, 4H2O), NaOH and acid oleic as raw materials. The synthesized powder was characterized by X-ray diffraction (XRD); it was used to determine the structural properties. The transmission electron microscopy and the scanning electron microscopy were used to determine the morphology and particle size. The Fourier Transform Infra-Red (FT-IR) spectroscopy is used to deduce the structural investigation and confirmation of ferrite. Raman spectroscopy is used to verify that we have synthesized CuxNi1−xFe2O4 and determines their phonon modes. The thermo gravimetric analysis findings allow the thermal cycle determination of samples whereas differential thermal analysis findings allow the phase transition temperature identification. The optical study UV–Visible is used to calculate the band gap energies. The vibrating sample magnetometer was used to obtain the hysteresis parameters. In conclude, the XRD confirmed the single phase spinel structure. The lattice constant increased with the increased copper contents. The size of nanoparticles decreased with the increased copper contents. The magnetic property of the CuxNi1−xFe2O4 shows remarkable changes with change of Cu2+.The variation of copper substitution has a significant influence on the optical, grain size and magnetic properties. The mean crystalline size of the synthesized ferrite was in the range of 14–43 nm.

Spin-Orbit Coupling (SOC) is a ubiquitous phenomenon in the spintronics area, as it plays a major role in allowing or enhancing many well-known phenomena, such as the Dzyaloshinskii-Moriya interaction, magnetocrystalline anisotropy, the Rashba effect, etc. However, the usual expression of the SOC interaction h/4 m(2)c(2) [E x p] . sigma (1) where p is the momentum operator, E the electric field, sigma the vector of Pauli matrices, breaks the gauge invariance required by the electronic Hamiltonian. On the other hand, very recently, a new phenomenological interaction, coupling the angular momentum of light and magnetic moments, has been proposed based on symmetry arguments: -xi/2[r x (E x B)] . M, (2) with M the magnetization, r the position, and xi the interaction strength constant. This interaction has been demonstrated to contribute and/or give rise, in a straightforward way, to various magnetoelectric phenomena, such as the anomalous Hall effect (AHE), the anisotropic magnetoresistance (AMR), the planar Hall effect and Rashba-like effects, or the spin -current model in multiferroics. This last model is known to be the origin of the cycloidal spin arrangement in bismuth ferrite for instance. However, the coupling of the angular momentum of light with magnetic moments lacked a fundamental theoretical basis. Starting from the Dirac equation, we derive a relativistic interaction Hamiltonian which linearly couples the angular momentum density of the electromagnetic (EM) field and the electrons spin ?. We name this coupling the Angular MagnetoElectric (AME) coupling. We show that in the limit of uniform magnetic field, the AME coupling yields an interaction exactly of the form of Eq. (2), thereby giving a firm theoretical basis to earlier works. The AME coupling can be expressed as: xi[E x A] . sigma-, (3) with A being the vector potential. Interestingly, the AME coupling was shown to be complementary to the traditional SOC, and together they restore the gauge invarianc

On the basis of the Dirac equation, a relativistic interaction Hamiltonian is derived which linearly couples the angular momentum density j of the electromagnetic (EM) field and the electron's spin sigma. The expectation value of this novel Hamiltonian is demonstrated to be precisely the recently proposed energy coupling the EM angular momentum density and magnetic moments [A. Raeliarijaona et al., Phys. Rev. Lett. 110, 137205 (2013)]. This previously overlooked Hamiltonian is also found to naturally result in the exact analytical form of the interaction energy inherent to the inverse Faraday effect, therefore demonstrating its relevance and easy use for the derivation of other complex magneto-optical and magnetoelectric effects originating from electron spin-light angular momentum couplings.

An applied stress field σ3 can reversibly change the temperature of an elastocaloric material under adiabatic conditions, and the temperature change Tσ3 is usually maximized near phase transitions.Using a thermodynamic approach, we demonstrate that an elastocaloric strength α = | Tσ3 |/|σ3| of 0.016 K/MPa can be achieved benefiting from the full first-order phase transition in BaTiO3 single crystals, which is comparable with typical elastocaloric materials reported in the literature. The elastocaloric temperature change is found to be giant (3.2 K) under a stress of 200 MPa with a temperature span of over 50 K, which can be significantly larger than its electrocaloric counterpart (∼1 K). Moreover, it is found that the elastocaloric strength can be remarkably enhanced (2.32 K/MPa) as long as the phase transition is triggered even by a modest stress near the sharp first-order phase transition, which is two orders of magnitude larger than those accomplished by full transition. Therefore, even a low stress (<30 MPa) can induce a modest elastocaloric effect (1.3 K) comparable with the electrocaloric counterpart, which is accompanied by a reduction of the working temperature span. In addition, it is found that the electrocaloric peak under tensile stresses moves towards higher temperatures with its magnitude slightly enhanced. Hopefully, our study will stimulate further investigations on elastocaloric and stress-mediated electrocaloric effects in ferroelectrics.

An applied stress field σ3 can reversibly change the temperature of an elastocaloric material under adiabatic conditions, and the temperature change Tσ3 is usually maximized near phase transitions.Using a thermodynamic approach, we demonstrate that an elastocaloric strength α = | Tσ3 |/|σ3| of 0.016 K/MPa can be achieved benefiting from the full first-order phase transition in BaTiO3 single crystals, which is comparable with typical elastocaloric materials reported in the literature. The elastocaloric temperature change is found to be giant (3.2 K) under a stress of 200 MPa with a temperature span of over 50 K, which can be significantly larger than its electrocaloric counterpart (∼1 K). Moreover, it is found that the elastocaloric strength can be remarkably enhanced (2.32 K/MPa) as long as the phase transition is triggered even by a modest stress near the sharp first-order phase transition, which is two orders of magnitude larger than those accomplished by full transition. Therefore, even a low stress (<30 MPa) can induce a modest elastocaloric effect (1.3 K) comparable with the electrocaloric counterpart, which is accompanied by a reduction of the working temperature span. In addition, it is found that the electrocaloric peak under tensile stresses moves towards higher temperatures with its magnitude slightly enhanced. Hopefully, our study will stimulate further investigations on elastocaloric and stress-mediated electrocaloric effects in ferroelectrics.

The polarization screening mechanism and ferroelectric phase stability of ultrathin BaTiO3 films exposed to water molecules is determined by first principles theory and in situ experiment. Surface crystallography data from electron diffraction combined with density functional theory calculations demonstrate that small water vapor exposures do not affect surface structure or polarization. Large exposures result in surface hydroxylation and rippling, formation of surface oxygen vacancies, and reversal of the polarization direction. Understanding interplay between ferroelectric phase stability, screening, and atomistic processes at surfaces is a key to control low-dimensional ferroelectricity., QC 20110418