Field-induced Structural Transition Research Articles

Deciphering the peculiar hysteresis loops of 0.05Pb(Mn1/3Sb2/3)O3–0.95Pb(Zr0.52Ti0.48)O3 piezoelectric ceramics

The majority of piezoelectric ceramics based on Pb(Zr, Ti)O3 (PZT) exhibit hysteretic behavior, which varies depending on various factors, including composition, microstructure and processing conditions. The ternary system 0.05Pb(Mn1/3Sb2/3)O3–0.95Pb(Zr0.52Ti0.48)O3 (5PMS-PZT) has shown attractive piezoelectric properties with superior thermal stability compared to pure Pb(Zr0.52Ti0.48)O3, but the underlying mechanisms of its complex hysteretic behavior have not been fully clarified yet. This work further delves into the hysteretic aspects of 5PMS-PZT ceramics and describes hysteresis features that have not been yet reported for any known piezoelectric system. Four current peaks in I-E loops and S-E loops with unconventional shapes, which have a significant dependence on applied field amplitude, frequency and electrical history have been observed here. This peculiar hysteretic behavior is influenced by convoluted effects of domain switching, electric field-induced structural transitions, point defects and aging/de-aging processes, whose combinations lead to unique hysteresis features.

Enhanced electrical magnetochiral effect by spin-hedgehog lattice structural transition

Nonreciprocal resistance, depending on both directions of current ($j$) and magnetic-field ($H$) or magnetization ($M$), is generally expected to emerge in a chiral conductor, and be maximized for $j$ $\parallel$ $H$($M$). This phenomenon, electrical magnetochiral effect (eMChE), is empirically known to increase with $H$ in a paramagnetic or fully ferromagnetic state on chiral lattice or to depend on fluctuation properties of a helimagnetic state. We report here the eMChE over a wide temperature range in the chiral-lattice magnet MnGe in which the spin hedgehog lattice (HL) forms with the triple spin-helix modulation vectors. The magnitude of nonreciprocal resistivity is sharply enhanced in the course of the field-induced structural transition of HL from cubic to rhombohedral form. This is attributed to the enhanced asymmetric electron scatterings by vector spin chirality in association with the large thermal fluctuations of spin hedgehogs.

Structural transition and magnetic properties of Mn doped Bi0.88Sm0.12FeO3 ceramics.

We investigated the effects of Mn doping on the crystal structure, phonon vibration, and magnetic properties of Bi0.88Sm0.12FeO3 ceramics. Mn doping effectively modified the rhombohedral symmetry and induced a structural transition from an R3c rhombohedral to Pnam orthorhombic structure. Magnetic measurements revealed a weak ferromagnetic behavior, which was related to the canted antiferromagnetic order of the Pnam structure. The cycloidal spin structure of the R3c phase could not be suppressed by substitution of Mn at the Fe site. Studies on the self-phase transition and electric field-induced structural transition revealed many changes in coercivity and remanent magnetization, which are believed to originate from the R3c/Pnam phase switching along with spin frustration. Observations of the field step-dependent hysteresis loop and the ferromagnetic-like hysteresis loop after poling in an electric field provided direct evidence of phase boundary (PB) ferromagnetism and magnetic coupling at the PB.

Electric field-induced structural transition of domain walls in nanoconfined nematic liquid crystal systems

ABSTRACTThe electric field-induced structural transition of domain walls in nanoconfined nematic liquid crystal systems was investigated on the basis of Landau–de Gennes theory. Two models of nanoconfined domain wall systems were established as splay–bend and twist wall systems under Fréedericksz transitions with two different rotation directions under the effect of electric field E/E0. Results showed that two structural transition processes occur in both models. Pincement transition occurs under a critical external field Ec1/E0. In pincement transition, walls change into two squeezed symmetric surface defects with opposite charges. Surface defects spread along the direction of the substrates and attain surface order reconstruction states as E/E0 is enhanced to Ec2/E0. The increment in cell gap d from the nanoscale to the microscale will not affect Ec2/E0 in both models.

Effects of external magnetic field and hydrostatic pressure on magnetic and structural phase transitions in Pr0.6Sr0.4MnO3

We investigate the effect of hydrostatic pressure on the temperature dependence of magnetization and also the influence of magnetic field on the linear thermal expansion in polycrystalline Pr0.6Sr0.4MnO3, which is ferromagnetic at room temperature (TC = 305 K) but its magnetization undergoes an abrupt decrease at TS = 89 K within the ferromagnetic state. Normal and inverse magnetocaloric effects around TC and TS, respectively, were reported earlier in this single phase compound [Repaka et al., J. Appl. Phys. 112, 123915 (2012)]. The thermal expansion shows an abrupt decrease at TS in zero magnetic field but transforms into an abrupt increase at the same temperature under 7 T, which we interpret as a consequence of magnetic field-induced structural transition from the low-temperature monoclinic (I2/a symmetry) to high-temperature orthorhombic (Pnma symmetry) phase in corroboration with a published neutron diffraction study in zero magnetic field. While the external magnetic field does not change TS, the application of a hydrostatic pressure of P = 1.16 GPa shifts the magnetic anomaly at TS towards high temperature. The pressure induced shift of the low-temperature magneto-structural anomaly (ΔTS = 27 K) is nine-times higher than that of the ferromagnetic Curie temperature (ΔTC = 3 K). Our results suggest that while the hydrostatic pressure stabilizes the low temperature monoclinic phase at the expense of the orthorhombic phase, the applied magnetic field does not affect the structural transition temperature.

Field-Induced Antipolar-Polar Structural Transformation and Giant Electrostriction in Organic Crystal.

The field-induced antipolar-polar structural transition in an organic antiferroelectric 2-trifluoromethylnaphthimidazole crystal is investigated by performing synchrotron X-ray diffraction. The polarities of all of the hydrogen-bonded chains become parallel with each other in the presence of an external electric field. The switching is accompanied by a giant electrostriction, which provides 1 order of magnitude larger strain than the piezoelectric strain of the organic ferroelectrics: croconic acid and poly(vinylidene fluoride); however, it is comparable to those of typical commercial piezoelectric ceramics. The crystal structure analysis with electric field shows that the origin of the observed giant electrostriction can be attributed to the shear strain that emerges from the polarity switching of the hydrogen-bonded chains. The antipolar-polar structural transition in antiferroelectrics could be employed for the development of high-performance electrostrictive organic materials.

Temperature- and field-induced structural transitions in magnetic colloidal clusters.

Magnetic colloidal clusters can form chain, ring, and more compact structures depending on their size. In the present investigation we examine the combined effects of temperature and external magnetic field on these configurations by means of extensive Monte Carlo simulations and a dedicated analysis based on inherent structures. Various thermodynamical, geometric, and magnetic properties are calculated and altogether provide evidence for possibly multiple structural transitions at low external magnetic field. Temperature effects are found to overcome the ordering effect of the external field, the melted stated being associated with low magnetization and a greater compactness. Tentative phase diagrams are proposed for selected sizes.

Field-Induced Structural Transition in the Bond Frustrated Spinel ZnCr2Se4**Supported by the National Basic Research Program of China under Grant No 2011CBA00111, and the National Natural Science Foundation of China under Grant No U1332143.

The effect of an external magnetic field on the structural and magnetic properties of bond frustrated ZnCr2Se4 at low temperatures is investigated using magnetization, dielectric constants and thermal conductivity experiments. With an increase in the magnetic field H, the antiferromagnetic transition temperature TN is observed to shift progressively toward lower temperatures. The corresponding high temperature cubic (Fd3̄m) to low temperature tetragonal (I41amd) structural transition is tuned simultaneously due to the inherent strong spin-lattice coupling. In the antiferromagnetic phase, an anomaly at HC2 defined as a steep downward peak in the derivative of the M–H curve is clearly drawn. It is found that TN versus H and HC2 versus T exhibit a consistent tendency, indicative of a field-induced tetragonal (I41amd) to cubic (Fd3̄m) structural transition. The transition is further substantiated by the field-dependent dielectric constant and thermal conductivity measurements. We modify the T–H phase diagram, highlighting the coexistence of the paramagnetic state and ferromagnetic clusters between 100 K and TN.

Synthesis and characterization of NiMnIn nanoparticles

Abstract The off-stoichiometric Ni 50 Mn 34 In 16 intermetalic Heusler nanoparticles have been prepared by laser ablation in distilled water from the target alloy using femtosecond laser system. The properties of the particles were characterized by electron microscopy and magnetometer techniques. The particle mean size of 28 nm was estimated by using the scanning electron microscopy images. However, the transmission electron microscopy results revealed that spherical cluster-like particles have been also produced. The magnetic field-induced structural transition was found in the particles with a starting temperature of around 250 K.

Magnetic response of polycrystalline YBaCo4O7+δ synthesized through the physical and chemical route: The role of phase inhomogeneities

Polycrystalline YBaCo4O7+δ samples were obtained through a standard solid state reaction, and their structural, morphological, electrical, and magnetic properties are carefully studied. The X-ray powder diffraction (XRD) patterns showed reflections of a pure hexagonal structure (space group P63mc) with lattice parameters being very close to those reported in the literature. Although XRD analysis showed that the main phase present is 114, the presence of secondary phases could not be ruled out based solely on the XRD characterization. Indeed, sensitive SQUID magnetic measurements showed that the samples were affected by very small quantities of the 112 phase (YBaCo2O5.5), which typically manifests itself through a conspicuous increase in the magnetization at~300K. The results achieved corroborated the predictions concerning the difficulty of stabilizing the 114 phase when synthesized via the standard solid-state reaction. With this in mind, we next attempted to obtain the compound with improved phase purity. In so doing, the YBaCo4O7+δ compound was synthesized through a wet chemistry method based on a citrates route. The XRD patterns recorded for these samples revealed well-defined peaks corresponding to a pure hexagonal structure. More interestingly, SQUID measurements show no sign of features in the M(T) curve at temperatures as low as~80K. This result was consistent with the magnetic behavior observed in YBaCo4O7+δ single-crystals. At temperatures below~80K, a clear feature was observed which seemed to correlate with a transition into an antiferromagnetic state. Isothermal magnetization recorded at 70K showed that field-induced effects manifested themselves through the appearance of a ferromagnetic-like component. This ferromagnetic component may arise from spin canting of the underlying antiferromagnetic state or through field-induced structural transition (at least at local scale). Although a definitive interpretation of the in-field behavior from magnetization data alone is difficult because of the unknown role of the yttrium ion, the results achieved suggest that the magnetic behavior observed in members of the R-114 family is not necessarily linked to the moment of the rare-earth ion, as in case of YBaCo4O7+δ, since the yttrium ion is not magnetic. Beyond this important finding, the experimental results reported in the present paper demonstrate that the tested chemical route is suitable for synthesizing complex, single-phase oxides, such as the YBaCo4O7+δ cobaltate. The success in synthesizing high-purity YBaCo4O7+δ allows one to subtract parasitic effects from the intrinsic magnetic behavior of this challenging system.

Electric field driven self-assembly of ionic microgels

We study, using fluorescent confocal laser scanning microscopy, the directed self-assembly of cross-linked ionic microgels under the influence of an applied alternating electric field at different effective packing fractions ϕeff in real space. We present a detailed description of the contribution of the electric field to the soft interparticle potential, and its influence on the phase diagram as a function of ϕeff and field strength E at a constant frequency of 100 kHz. In our previous work [Mohanty et al., Soft Matter, 2012, 8, 10819], we demonstrated the existence of field-induced structural transitions both at low and high ϕeff. In this work, we revisit the phase behavior at low and intermediate ϕeff with a focus on both structure and dynamics. We demonstrate the existence of various field induced transitions such as an isotropic fluid to string phase to body centered tetragonal (BCT) crystal phase at low concentrations and a reversible field-induced crystal (face centered cubic, FCC) to crystal (BCT) transition at intermediate concentrations. We also investigate the kinetics of the crystal–crystal transition and demonstrate that this occurs through an intermediate melting process. These results are discussed in the light of previous studies of dipolar hard and charged colloids.

Deformable particles with anisotropic interactions: unusual field-induced structural transitions in ultrasoft ionic microgel colloids

Ionic microgels are intriguing soft and deformable colloids with an effective pair potential that crosses over from Yukawa-like at large distances to a much softer repulsive interaction at short distances. Here we report the effect of adding an anisotropic dipolar contribution to colloids with such “ultra-soft” interactions. We use an alternating electric field to induce a tunable dipolar contribution, and study the resulting particle self-assembly and phase transitions in situ with confocal laser scanning microscopy. We find significant field-induced structural transitions at low as well as at very high effective volume fractions. At ϕeff = 0.1 we observe a transition from an isotropic to a string fluid. At ϕeff = 0.85, there is a reversible transition from an amorphous to a dipolar crystalline state, followed by the onset of a gas–(string) solid coexistence. At ϕeff = 1.6 and 2.0, i.e. far above close packing, evidence for a field-induced arrested phase separation is found.

Magnetic and calorimetric investigations of inverse magnetocaloric effect in Pr0.46Sr0.54MnO3

We investigated magnetic entropy change (ΔSm) in the A-type antiferromagnet Pr0.46Sr0.54MnO3 by magnetic and differential scanning calorimetry (DSC) methods. The field-induced antiferromagnetic to ferromagnetic transition is first-order in nature and is accompanied by a large change in the latent heat as evidenced by the DSC data. The ΔSm shows an inverse magnetocaloric effect (ΔSm=+9 J kg−1 K−1 for ΔH=7 T) around the Neel temperature (TN=210±2 K) by magnetic measurement, which closely agrees with the calorimetric results. It is suggested that the large positive ΔSm results from a field-induced structural transition that accompanies the destruction of antiferromagnetism.

Nanoscale resistance switching in manganite thin films: Sharp voltage threshold and pulse-width dependence

We report the local-conductivity properties of a ${\text{La}}_{0.8}{\text{Ca}}_{0.2}{\text{MnO}}_{3}$ thin film, studied by conductive atomic force microscopy. Nonvolatile and bipolar reversible switching of nanometer-sized regions was observed. A threshold voltage, ${U}_{c}\ensuremath{\approx}3\text{ }\text{V}$, and a logarithmic pulse-width dependence compatible with domain-wall creep were revealed. The results are difficult to explain in terms of an ionic drift scenario but rather indicate a switching mechanism based on orbital and accompanying structural changes. A phenomenological model of an electric field-induced structural transition is proposed.

Strong interplay between magnetic and structural properties in the spin-12chain molecular compoundD-F5PNN

We present elastic and inelastic neutron scattering results on spin-1/2 chain antiferromagnet $\text{D-}{\mathrm{F}}_{5}\text{PNN}$. We show that a structural transition occurs in zero field below ${T}_{c}\ensuremath{\sim}710\text{ }\text{mK}$ from $C2/c$ space group (uniform chains) to $Pc$ (bond-alternating chains). When applying a magnetic field at 50 mK, the space group gets back to $C2/c$ above ${H}_{c1}\ensuremath{\sim}1\text{ }\text{T}$. From the dispersion curves of the magnetic excitations measured at $T=50\text{ }\text{mK}$, we determine the values of the exchange parameters at 0 and 9 T, which evidence that the magnetic field makes the chains evolve from alternating to uniform. This change in behavior can be correlated unambiguously with the field-induced structural transition. These results evidence ``mirror'' field- and temperature-induced magnetocrystalline transitions.

Magnetic-field-induced transformation in FeMnGa alloys

A kind of ferromagnetic shape memory alloy with off-stoichiometric composition of Heusler alloy Fe2MnGa has been synthesized. By optimizing composition, the martensitic transformation has been modified to occur at about 163 K accompanying spontaneous magnetization, which enables a magnetic field-induced structural transition from a paramagnetic parent phase to a ferromagnetic martensite with high magnetization of 93.8 emu/g. The material performs a quite large lattice distortion through the transformation, (c−a)/c=33.5%, causing a shape memory strain upto 3.6%. Such large lattice distortions strongly influence the electron structures, and thus some special physical behavior related to the transport and conductive properties is investigated.

Field-induced structural transition and the related magnetic entropy change in Ni 43Mn 43Co 3Sn 11 alloy

Magnetic properties and magnetic entropy change Δ S were investigated in Heusler alloy Ni 43Mn 43Co 3Sn 11. With decreasing temperature this alloy undergoes a martensitic structural transition at T M=188 K. The incorporation of Co atoms enhances ferromagnetic exchange for parent phases. Austenitic phase with cubic structure shows strong ferromagnetic behaviors with Curie temperature T C A at 346 K, while martensitic phase shows weak ferromagnetic properties. An external magnetic field can shift T M to a lower temperature at a rate of 4.4 K/T, and a field-induced structural transition from martensitic to austenitic state takes place at temperatures near but below T M. As a result, a great magnetic entropy change with positive sign appears. The size of Δ S reaches 33 J/kg K under 5 T magnetic field. More important is that the Δ S displays a table-like peak under 5 T, which is favorable for Ericsson-type refrigerators.

Metastability and magnetic memory effect inNi2Mn1.4Sn0.6

Magnetostructural instability in the ferromagnetic shape memory alloy of composition ${\mathrm{Ni}}_{2}{\mathrm{Mn}}_{1.4}{\mathrm{Sn}}_{0.6}$ is investigated by transport and magnetic measurements. Large negative magnetoresistance is observed around the martensitic transition temperature $(90--210\phantom{\rule{0.3em}{0ex}}\mathrm{K})$. Both magnetization and magnetoresistance data indicate that upon the application of an external magnetic field at a constant temperature, the sample attains a field-induced arrested state which persists even when the field is withdrawn. We observe an intriguing behavior of the arrested state that it can remember the last highest field it has experienced. The field-induced structural transition plays the key role for the observed anomaly and the observed irreversibility can be accounted for by the Landau-type free energy model for the first-order phase transition.

Magnetoresistance and field-induced structural transitions in Ni 50Mn 50−xSn x Heusler alloys

Large magnetoresistance effects were observed in Ni 50Mn 50− x Sn x Heusler alloys for concentrations 13⩽ x⩽16. The effects occur at the respective martensitic transition temperatures ( T M), which can be tuned in temperature through variations in Sn concentration. The largest observed values of the magnetoresistance (Δ ρ/ ρ o) were −42% for x=14 at T≈250 K, and −23% above room temperature ( T≈320 K) for the sample with x=13, where the magnetic field change was Δ H=5 T. Magnetization and X-ray diffraction measurements indicate that the origin of the observed magnetoresistance is a magnetically induced magnetostructural transition from a complex 10 M modulated orthorhombic phase containing some antiferromagnetic coupling to a ferromagnetic cubic L2 1 structure.

Magnetism and heat capacity ofDy5Si2Ge2

Magnetic and thermal properties of the compound ${\mathrm{Dy}}_{5}{\mathrm{Si}}_{2}{\mathrm{Ge}}_{2}$ (orthorhombic, ${\mathrm{Sm}}_{5}{\mathrm{Ge}}_{4}$--type) have been studied. This compound orders antiferromagnetically at $56\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ $({T}_{N})$, with a positive paramagnetic Curie temperature $({\ensuremath{\theta}}_{P})$ indicating the presence of competing magnetic interactions. Zero-field-cooled and field-cooled magnetization data obtained in a low field of $5\phantom{\rule{0.3em}{0ex}}\mathrm{mT}$ show irreversibility that starts above ${T}_{N}$, giving rise to a deviation from the paramagnetic Curie-Weiss behavior, in the temperature range of $56--100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Magnetization vs field ($M$ vs $H$) isotherms below $40\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ display a metamagnetic transition (MMT) and at $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, a sharp, martensiticlike, step in magnetization at a critical field of $\ensuremath{\sim}2.9\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. Heat capacity measurements on this compound in zero applied field exhibit a peak at ${T}_{N}$ which gets subsequently suppressed on application of magnetic fields of $5\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ and $9\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. The MMT is found to have a dominant role in the associated magnetocaloric effect. The isothermal entropy change $(\ensuremath{\Delta}{S}_{m})$ and the adiabatic temperature change $(\ensuremath{\Delta}{T}_{\mathrm{ad}})$ are found to be $\ensuremath{\sim}8\phantom{\rule{0.3em}{0ex}}\mathrm{J}∕\mathrm{mol}\phantom{\rule{0.2em}{0ex}}\mathrm{K}$ and $\ensuremath{\sim}6\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, respectively, for $9\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ field change, in the vicinity of ${T}_{N}$. The reversible metamagnetic behavior is envisaged to arise from strong magnetocrystalline anisotropy and/or due to a possible field-induced structural transition as observed in the isostructural ${\mathrm{Gd}}_{5}{\mathrm{Ge}}_{4}$ compound.