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Dielectric investigations in unconventionally processed TbMnO3 ceramics
Abstract
TbMnO3 ceramics with enhanced dielectric properties were synthesized by an innovative route combining high-energy ball milling and hot-forging sintering. Dielectric investigations reveal the presence of two distinct relaxation processes: one thermally activated mostly due to dipolar effects and other related to the movement of polar clusters or electric dipoles. Long-range polar order was not achieved, as ferroelectricity in TbMnO3 is strongly dependent on the crystallographic direction. A distribution of relaxation times indicates a cooperative response of the electric dipoles.
... Because of the wide applications, more and more studies focus on these materials. TbMn O 3 (TMO), a typical perovskite, shows the obvious relaxations at high and low temperature with different mechanisms, respectively [9,10]. Properties of traditional perovskite composite oxides are usually unsophisticated, however they can be improved by partly replacing ions in A or (and) B site [11][12][13]. ...
... Properties of traditional perovskite composite oxides are usually unsophisticated, however they can be improved by partly replacing ions in A or (and) B site [11][12][13]. Therefore, most studies have focused on the doped TMO [9,10,[14][15][16][17][18][19][20][21][22]. The high dielectric constant (4 10 4 ) effect was observed at the high temperature and low frequency regions in La-doped TMO [16], which linked with Maxwell-Wagner polarization from grain-grain boundaries and the electrode interface. ...
The ceramic composites of Tb1-xFexMnO3 (x=0.05, 0.1, 0.2, 0.3, 0.4) were synthesized by conventional solid-state reaction. The dielectric constants and loss of composites as a function of temperature (from 77 to 350 K) and frequency (from 0.1 to 200 kHz) were measured. Interestingly, in all composites, Tb0.95Fe0.05MnO3 sample not only enjoys the highest dielectric constants (similar to 10(4)) in the high temperature and low frequency range, but also presents the lowest loss in the high frequency range. Debye-like dielectric dissipation peaks shift to high temperature range with the increase of frequency, which become unobvious in high iron content doping samples. Analysis indicates that the perovsldte structures gradually change with the increase of Fe content and the dielectric properties of TbMnO3 can be improved by adding Fe with appropriate content.
... The samples were synthesized as previously reported [8] by using HEBM with stoichiometric amounts of analytical-grade (Alfa-Aesar) Tb 4 O 7 and MnO 2 as initial powders, following the ratio Tb 4 O 7 :MnO 2 = 1:4. The nanopowders were processed in a Retsch PM 100 planetary ball mill for 12 h at 400 rpm by using zirconium oxide vial and balls. ...
... Considering the second HEBM, the best condition for nanostructuration was achieved after 24 h of milling. These powders were reduced to fine particles (Fig. 2c), with a critical diameter of 248 nm and a log-normal distribution (Fig. 2c, inset), which is typical of HEBM samples [8,[12][13][14]. The annealing atmosphere had no influence on the final particles size. ...
Nanostructured orthorhombic TbMnO3 polycrystals were synthesized by high-energy ball milling and annealing in Ar or O2 atmospheres. Oxygen annealed samples show shrunken unit cells in comparison with Ar annealed ones, without Mn valence changes in both cases. Magnetic and dielectric investigations show strong evidence of long-range (43 K) and quasi-long-range (9 K) ordering for Mn and Tb ions, respectively, and a noncollinear spin-spiral magnetic ordering of Mn spins, with higher magnetic response and ferroelectric state for argon synthesized samples.
We have studied the optical and thermal properties of terbium manganate (TbMnO3) nanoparticles at room temperature. The sample is successfully synthesized by sol–gel method. An orthorhombic phase of the sample is confirmed from XRD analysis. The Williamson–Hall analysis is done to study the contribution of strain and crystallite size on the peak broadening of the synthesized nanoparticles. Elemental analysis of the sample is evaluated from the EDX profile. TbMnO3 nanoparticles exhibit strong absorption in the UV region. The optical band gap is calculated using the Tauc method from UV–Vis absorption spectroscopic analysis. Urbach energy is found to be 0.28 eV for the existence of band distortion and defects in the material. Thermal behaviour of these nanoparticles is determined by non-isothermal thermogravimetric analysis at inert atmosphere. The effect of different heating rates (10, 12, 15 and 20 K/min) on thermal properties of the sample is also investigated. The kinetic parameters are evaluated using different model-free methods in the analysis of solid-state kinetics for thermal behaviour of TbMnO3 nanoparticles. The Coats–Redfern method is used here to determine the apparent reaction order which is found to be ~ 2.
Recent research activities on the linear magnetoelectric (ME) effect---induction of magnetization by an electric field or of polarization by a magnetic field---are reviewed. Beginning with a brief summary of the history of the ME effect since its prediction in 1894, the paper focuses on the present revival of the effect. Two major sources for 'large' ME effects are identified. (i) In composite materials the ME effect is generated as a product property of a magnetostrictive and a piezoelectric compound. A linear ME polarization is induced by a weak ac magnetic field oscillating in the presence of a strong dc bias field. The ME effect is large if the ME coefficient coupling the magnetic and electric fields is large. Experiments on sintered granular composites and on laminated layers of the constituents as well as theories on the interaction between the constituents are described. In the vicinity of electromechanical resonances a ME voltage coefficient of up to 90 V cm-1 Oe-1 is achieved, which exceeds the ME response of single-phase compounds by 3-5 orders of magnitude. Microwave devices, sensors, transducers and heterogeneous read/write devices are among the suggested technical implementations of the composite ME effect. (ii) In multiferroics the internal magnetic and/or electric fields are enhanced by the presence of multiple long-range ordering. The ME effect is strong enough to trigger magnetic or electrical phase transitions. ME effects in multiferroics are thus 'large' if the corresponding contribution to the free energy is large. Clamped ME switching of electrical and magnetic domains, ferroelectric reorientation induced by applied magnetic fields and induction of ferromagnetic ordering in applied electric fields were observed. Mechanisms favouring multiferroicity are summarized, and multiferroics in reduced dimensions are discussed. In addition to composites and multiferroics, novel and exotic manifestations of ME behaviour are investigated. This includes (i) optical second harmonic generation as a tool to study magnetic, electrical and ME properties in one setup and with access to domain structures; (ii) ME effects in colossal magnetoresistive manganites, superconductors and phosphates of the LiMPO4 type; (iii) the concept of the toroidal moment as manifestation of a ME dipole moment; (iv) pronounced ME effects in photonic crystals with a possibility of electromagnetic unidirectionality. The review concludes with a summary and an outlook to the future development of magnetoelectrics research.
In this paper, the ferroic properties of polycrystalline LuFe2O4 samples were carefully investigated, and a dissimilar charge ordered state was identified. Strong dielectric dispersion, between 350 K and 225 K; the formation of cluster glass magnetic phases in the same temperature range; and the existence of a ferrimagnetic transition at 230 K indicate the coupling between the ferroelectric and the magnetic orders. Mössbauer spectroscopic investigations, at room temperature, revealed unbalanced contributions of the ferric and ferrous iron ions to the charge ordered state.
In spite of intrinsic limitations, neutron powder diffraction is, and will still be in the future, the primary and most straightforward technique for magnetic structure determination. In this paper some recent improvements in the analysis of magnetic neutron powder diffraction data are discussed. After an introduction to the subject, the main formulas governing the analysis of the Bragg magnetic scattering are summarized and shortly discussed. Next, we discuss the method of profile fitting without a structural model to get precise integrated intensities and refine the propagation vector(s) of the magnetic structure. The simulated annealing approach for magnetic structure determination is briefly discussed and, finally, some features of the program FullProf concerning the magnetic structure refinement are presented and discussed. The different themes are illustrated with simple examples.
The magnetic structures which endow TbMnO with its multiferroic
properties have been reassessed on the basis of a comprehensive soft x-ray
resonant scattering (XRS) study. The selectivity of XRS facilitated separation
of the various contributions (Mn edge, Mn 3d moments; Tb M edge, Tb
4f moments), while its variation with azimuth provided information on the
moment direction of distinct Fourier components. When the data are combined
with a detailed group theory analysis, a new picture emerges of the
ferroelectric transition at 28 K. Instead of being driven by the transition
from a collinear to a non-collinear magnetic structure, as has previously been
supposed, it is shown to occur between two non-collinear structures.
We present a detailed dielectric study of the relaxation effects that occur in several perovskite rare-earth manganites, including the multiferroics TbMnO(3) and DyMnO(3). We demonstrate that the strong magnetocapacitive effects, observed for electrical fields E parallel c, are nearly completely governed by magnetic-state induced changes of the relaxation parameters. The multiferroic materials, which undergo a transition into a spiral magnetic state, show qualitatively different relaxation behavior than those compounds transferring into an A-type antiferromagnetic state. We ascribe the relaxations in both cases to the off-center motion of the manganese ions, which in the multiferroic systems also leads to the ferroelectric ordering.
We carry out a first-principles theoretical study of the magnetically induced polarization in orthorhombic TbMnO3, a prototypical material in which a cycloidal-spin structure generates an electric polarization via the spin-orbit interaction. We compute both the electronic and the lattice-mediated contributions to the polarization and find that the latter is strongly dominant. We analyze the spin-orbit induced forces and lattice displacements from both atomic and mode-decomposition viewpoints, and show that a simple model based on nearest Mn-Mn neighbor Dzyaloshinskii-Moriya interactions is not able to account fully for the results. The direction and magnitude of our computed polarization are in good agreement with experiment.
Magnetoelectric multiferroics combine ferromagnetism (a spontaneous magnetization that can be switched by a magnetic field)
and ferroelectricity (a spontaneous electric polarization that can be switched by an electric field) in the same phase. They
have tremendous potential for applications, not only because they possess the properties of both parent phenomena, but also
because coupling between ferromagnetism and ferroelectricity can lead to additional novel effects. In their Perspective,
Spaldin and Fiebig
discuss the factors behind the recent resurgence of interest in magnetoelectric multiferroics, describe some exciting results
emerging from the current research activities, and point to important challenges and directions for future work.
In general, a dielectric is considered as a non-conducting or insulating material (such as a ceramic or polymer used to manufacture a microelectronic device). This book describes the laws governing all dielectric phenomena.
Multiferroic magnetoelectrics are materials that are both ferromagnetic and ferroelectric in the same phase. As a result, they have a spontaneous magnetization that can be switched by an applied magnetic field, a spontaneous polarization that can be switched by an applied electric field, and often some coupling between the two. Very few exist in nature or have been synthesized in the laboratory. In this paper, we explore the fundamental physics behind the scarcity of ferromagnetic ferroelectric coexistence. In addition, we examine the properties of some known magnetically ordered ferroelectric materials. We find that, in general, the transition metal d electrons, which are essential for magnetism, reduce the tendency for off-center ferroelectric distortion. Consequently, an additional electronic or structural driving force must be present for ferromagnetism and ferroelectricity to occur simultaneously.
Scitation is the online home of leading journals and conference proceedings from AIP Publishing and AIP Member Societies
Highly dense, single-phase nanostructured ceramics of the 0.8BiFeO3–0.2BaTiO3 multiferroic compound were prepared by mechanosynthesis. Their structural, microstructural and ferroic properties have been significantly improved by means of preventing the formation of residual phases through the mechanosynthesis protocol, mainly by the formation of a monoclinic solid solution (Cm space group), which is reported for multiferroic solid solutions for the first time. Improved remanent polarization and magnetization were obtained and determined as being 2.0 μC cm−2 and 0.02 emu g−1.
In the last few years, there have been many studies on the dielectric properties of magnetic oxides, mostly in the aspect of the coupling between ferroelectricity and magnetism. These studies have been focused on dielectric anomalies at the magnetic transition temperature, the magnetodielectric effect, the magnetic relaxor ferroelectricity, materials with high dielectric constants, etc. However, it appears that some of these studies were based on an erroneous interpretation of the dielectric functions measured by using LCR meters. Here, we report rare examples of two-step dielectric anomalies in TbMnO3 and Bi2Fe4O9 that show peculiar frequency dependences. We point out that the thermally-activated charge carriers in isolated impurities are the most probable origin of the dielectric anomalies with the typical relaxor-like frequency dependence.
The complex dielectric properties for ceramic samples of TbMnO3 were investigated as functions of temperature (100 K⩽T⩽360 K) and frequency (100 Hz⩽f⩽100 kHz). Two thermally activated dielectric relaxations were found with the activation energies of 0.30 and 0.22 eV for the high- and low-temperature relaxations, respectively. By means of complex impedance analysis the high-temperature relaxation was identified to originate from the internal barrier-layer capacitor effects related to the grain boundaries, and the low-temperature relaxation was ascribed to the dipolar effects induced by charge-carrier-hopping motions inside the grains.
The crystal and magnetic structures of Tb1-xCaxMnO3 series have been studied by x-ray and neutron-diffraction techniques. Macroscopic magnetic properties have been characterized using ac magnetic susceptibility measurements. The relationships between structural and magnetic behaviors are discussed. Our study shows that the magnetism of manganese in this system is very complex due to the small size of the rare earth. TbMnO3 does not develop a simple A-type magnetic order, as does LaMnO3, but an incommensurate sinewave structure. As the Ca content increases up to x=0.33, the magnetization increases without, however, reaching a truly ferromagnetic state. Instead, the magnetic ground state is composed of ferromagnetic clusters in a paramagnetic matrix. Charge ordering is observed at higher values of x and the magnetic ground state evolves, with increasing x values, from the CE type to a mixture of different magnetic structures including some noncollinear structures. For x=0.85, we observe a phase segregation at low temperatures into an orthorhombic phase and a monoclinic phase.
Magnetoelectric multiferroics is an old but emerging class of materials that combine coupled electric and magnetic dipole order. In these materials, ferroelectric and magnetic (ferromagnetic or antiferromagnetic) states coexist or compete with each other. The interaction leads to a so-called magnetoelectric effect, which is the induction of magnetization by an electric field or electric polarization by a magnetic field. In the past few years, a new set of magnetoelectric multiferroics such as TbMnO3 and Ni3V2O8 has been discovered. In these magnetoelectric multiferroics, ferroelectric order develops upon a magnetic phase transition into a spiral magnetic ordered phase. In addition, these systems show large magnetoelectric effects accompanied by metamagnetic transitions. Noncollinear spiral magnetism is the key to understanding the magnetoelectric properties in these systems. Here I discuss the magnetoelectric coupling in spiral magnets and review recent advances in the understanding of ferroelectr...
Cross correlation between magnetism and electricity in a solid can host magnetoelectric effects, such as magnetic (electric) induction of polarization (magnetization). A key to attain the gigantic magnetoelectric response is to find the efficient magnetism-electricity coupling mechanisms. Among those, recently the emergence of spontaneous (ferroelectric) polarization in the insulating helimagnet or spiral-spin structure was unraveled, as mediated by the spin-exchange and spin-orbit interactions. The sign of the polarization depends on the helicity (spin rotation sense), while the polarization direction itself depends on further details of the mechanism and the underlying lattice symmetry. Here, we describe some prototypical examples of the spiral-spin multiferroics, which enable some unconventional magnetoelectric control such as the magnetic-field-induced change of the polarization direction and magnitude as well as the electric-field-induced change of the spin helicity and magnetic domain.
Using in-field single-crystal neutron diffraction, we have determined the magnetic structure of TbMnO(3) in the high field P parallel a phase. We unambiguously establish that the ferroelectric polarization arises from a cycloidal Mn spin ordering, with spins rotating in the ab plane. Our results demonstrate directly that the flop of the ferroelectric polarization in TbMnO(3) with applied magnetic field is caused from the flop of the Mn cycloidal plane.
The magnetoelectric effect--the induction of magnetization by means of an electric field and induction of polarization by means of a magnetic field--was first presumed to exist by Pierre Curie, and subsequently attracted a great deal of interest in the 1960s and 1970s (refs 2-4). More recently, related studies on magnetic ferroelectrics have signalled a revival of interest in this phenomenon. From a technological point of view, the mutual control of electric and magnetic properties is an attractive possibility, but the number of candidate materials is limited and the effects are typically too small to be useful in applications. Here we report the discovery of ferroelectricity in a perovskite manganite, TbMnO3, where the effect of spin frustration causes sinusoidal antiferromagnetic ordering. The modulated magnetic structure is accompanied by a magnetoelastically induced lattice modulation, and with the emergence of a spontaneous polarization. In the magnetic ferroelectric TbMnO3, we found gigantic magnetoelectric and magnetocapacitance effects, which can be attributed to switching of the electric polarization induced by magnetic fields. Frustrated spin systems therefore provide a new area to search for magnetoelectric media.
With the perovskite multiferroic RMnO3 (R = Gd, Tb, Dy) as guidance, we argue that the Dzyaloshinskii-Moriya interaction (DMI) provides the microscopic mechanism for the coexistence and strong coupling between ferroelectricity and incommensurate magnetism. We use Monte-Carlo simulations and zero temperature exact calculations to study a model incorporating the double-exchange, superexchange, Jahn-Teller and DMI terms. The phase diagram contains a multiferroic phase between A and E antiferromagnetic phases, in excellent agreement with experiments.
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