Field-induced Phase Transition Research Articles

Field-induced transitions in the Kitaev material α−RuCl3 probed by thermal expansion and magnetostriction

High-resolution thermal expansion and magnetostriction measurements were performed on single crystals of $\alpha$-RuCl$_3$ in magnetic fields applied parallel to the Ru-Ru bonds. The length changes were measured in the direction perpendicular to the honeycomb planes. Our data show clear thermodynamic characteristics for the field-induced phase transition at the critical field $\mu_0H_{c1} = 7.8(2)$ T where the antiferromagnetic zigzag order is suppressed. At higher fields, a kink in the magnetostriction coefficient signals an additional phase transition around $\mu_0H_{c2} \approx 11$ T. The extracted Gr\"uneisen parameter shows typical hallmarks for quantum criticality near $H_{c1}$, but also displays anomalous behavior above $H_{c1}$. We compare our experimental data with linear spin-wave calculations employing a minimal Kitaev-Heisenberg model in the semiclassical limit. Most of the salient features are in agreement with each other, however, the peculiar features in the high-field region above $H_{c1}$ cannot be accounted for in our modelling and hence suggest a genuine quantum nature. We construct a phase diagram for $\alpha$-RuCl$_3$ showing two low-temperature transitions induced by an in-plane field along the Ru-Ru bonds.

Itinerant metamagnetic transition in the ferromagnet LuCo3 induced by high field: Instability of the 3d -electron subsystem

$\mathrm{LuC}{\mathrm{o}}_{3}$ is an itinerant ferromagnet whose magnetic properties strongly depend on the position of the $3d$ electronic states relative to the Fermi level. Here, we report on the magnetization of a $\mathrm{LuC}{\mathrm{o}}_{3}$ single crystal in pulsed magnetic fields up to 58 T. We find a field-induced phase transition just below 50 T from a low-spin to a high-spin state. The transition shows a pronounced anisotropy of the magnetization jump and hysteresis. A series of ab initio calculations based on the density functional theory show that the transition is due to a significant change in the occupancies of the Co $3d$ electronic states. At the same time, some features in the majority spin density of the Co $3d$ states are slightly modified and pass through the Fermi level when the spin state is changed, which leads to the instability of the $3d$-electron subsystem. Thereby, the applied magnetic field causes a significant redistribution in the majority and minority spin states in the Co $3d$ subsystem, which results in the sharp change in the magnetization.

Ultrahigh field-induced strain in lead-free ceramics

Abstract Due to the worldwide concerns of environmental protection and sustainable development, lead-free piezoelectric materials are greatly desired for bridging the electrical energy to the mechanical energy. However, their lower energy conversion coefficient compared to the conventional lead-containing piezoelectric materials significantly limits their device applications. Herein, we introduce a novel strategy to increase the strain of lead-free ferroelectric system via material structure design to create polar nano regions (PNRs) and point defects in the material while retaining the global ferroelectric phase. This added short-range structural heterogeneity in the material will facilitate the field-induced phase transition and reversible domain wall switching to enhance the strain. Following this strategy, we demonstrate an ultrahigh strain induced by an electric field in non-textured lead-free Bi0.5Na0.5TiO3 (BNT)-based ceramics. The strain in unipolar mode (Suni) can reach up to 0.74% at 70 kV/cm, making it the highest value in reported lead-free ceramics so far. This puts forward a good route to design high-performance piezoelectric materials by material structure engineering. It also reveals the promising potential of lead-free piezoelectric materials in practical electromechanical device applications.

Observation of in-plane magnetic field induced phase transitions in FeSe

We investigate the thermodynamic properties of FeSe under the in-plane magnetic fields using torque magnetometry, specific heat, magnetocaloric measurements. Below the upper critical field Hc2, we observed the field-induced anomalies at H1 ~ 15 T and H2 ~ 22 T near H//ab and below a characteristic temperature T* ~ 2 K. The transition magnetic fields H1 and H2 exhibit negligible dependence on both temperature and field orientation. This contrasts with the strong temperature and angle dependence of Hc2, suggesting that these anomalies are attributed to the field-induced phase transitions, originating from the inherent spin-density-wave instability of quasiparticles near the superconducting gap minima or possible Flude-Ferrell-Larkin-Ovchinnikov state in the highly spin-polarized Fermi surfaces. Our observations imply that FeSe, an atypical multiband superconductor with extremely small Fermi energies, represents a unique model system for stabilizing unusual superconducting orders beyond the Pauli limit.

Enhanced Energy Storage Density of Lead Lutetium Niobate Crystals by Electric Field-Induced Secondary Phase Transition via Na/La Codoping.

As emerging materials for capacitor applications, antiferroelectric (AFE) materials possess high energy storage density. AFE single crystals are conducive to studying the physical mechanism of AFE response. However, the preparation of AFE single crystals is a huge and long-standing challenge. Herein, we report the effect of Na/La codoping on the energy storage properties and phase transition of Pb(Lu1/2Nb1/2)O3 (PLN) AFE single crystals. An enhanced recoverable energy storage density of 4.81 J/cm3 with a high energy efficiency of 82.36% is obtained, which is much larger than that of the PbZrO3- and PLN-based AFE crystals. Two superlattice reflections, which stem from the A-site Pb2+ ions and the ordered B-site ions, are identified by X-ray diffraction and selected-area electron diffraction. The domain structures demonstrated a high temperature stability of the AFE phase. A secondary ferroelectric phase transition is induced after codoping, resulting in a sharp improvement of polarization (12.5 μC/cm2), which contributes to the enormous enhancement of energy storage density. This multiphase transition is explained using the modified Ginzburg-Landau-Devonshire phenomenology.

Phase boundary and electric field induced polarization rotation in lead-free Ba(Zr0.2Ti0.8)O3-(Ba0.7Ca0.3)TiO3

ABSTRACT Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (BZT-xBCT) is a promising lead-free ferroelectric system with high piezoelectricity. Here we carry out phenomenological calculations to explore phase stability and electric field induced phase transition. Study of free energy variation near phase boundaries revealed ultralow energy barrier in single orthorhombic phase region and phase coexistence around inter-ferroelectric transitions. The calculated critical electric field for tetragonal-orthorhombic transition is in reasonable agreement with experimental data. Temperature–composition phase diagram under [001], [011] and [111] oriented electric field are computed, and polarization rotation associated monoclinic structures are studied.

Unexpected magnetic phase in the weakly ordered spin- 12 chain cuprate Sr2CuO3

We present the magnetic phase diagram of a spin-1/2 chain antiferromagnet Sr$_2$CuO$_3$ studied by ultrasound phase-sensitive detection technique. We observe an enhanced effect of external magnetic field on the ordering temperature of the system, which is in the extreme proximity to the quantum critical point. Inside the N\'eel ordered phase, we detect an additional field-induced continuous phase transition, which is unexpected for a collinear Heisenberg antiferromagnet. This transition is accompanied by softening of magnetic excitation mode observed by electron-spin resonance, which can be associated with a longitudinal (amplitude) mode of the order parameter in a weakly-coupled system of spin-1/2 chains. These results suggest transition from a transverse collinear antiferromagnet to an amplitude-modulated spin density wave phase induced by magnetic field.

High-field magnetoacoustics of a Dy2Fe14Si3 single crystal

Abstract Dy2Fe14Si3 (hexagonal crystal structure of the Th2Ni17 type) is a highly-anisotropic ferrimagnet with spontaneous magnetic moment Ms = 8 μB per formula unit (at 2 K), directed along the Fe sublattice, and Curie temperature TC = 500 K. The magnetic anisotropy is of the easy-plane type with the [100] axis as an easy magnetization direction. Large anisotropy is observed also within the basal plane. In fields applied along the [100] and [120] axes, field-induced phase transitions were observed at 33 T (of the first order) and at 41 T (of the second order), respectively (at 2 K). Relative changes of sound velocity and changes of sound attenuation at these phase transitions in a Dy2Fe14Si3 single crystal were measured in pulsed magnetic fields up to 58 T at 2 K and elevated temperatures. The performed theoretical analysis suggests that the interaction of the elastic subsystem with the magnetic one is of the exchange-striction nature.

High-field quantum disordered state in α−RuCl3 : Spin flips, bound states, and multiparticle continuum

Layered $\alpha$-RuCl3 has been discussed as a proximate Kitaev spin liquid compound. Raman and THz spectroscopy of magnetic excitations confirm that the low-temperature antiferromagnetic ordered phase features a broad Raman continuum, together with two magnon-like excitations at 2.7 and 3.6 meV, respectively. The continuum strength is maximized as long-range order is suppressed by an external magnetic field. The state above the field-induced quantum phase transition around 7.5 T is characterized by a gapped multi-particle continuum out of which a two-particle bound state emerges, together with a well-defined single-particle excitation at lower energy. Exact diagonalization calculations demonstrate that Kitaev and off-diagonal exchange terms in the Fleury-Loudon operator are crucial for the occurrence of these features in the Raman spectra. Our study firmly establishes the partially-polarized quantum disordered character of the high-field phase.

Dielectric response and magneto-electric interaction of La1.67Sr0.33NiO4 single crystal

The dielectric response of La1.67Sr0.33NiO4 single crystal varies with the frequency, temperature and magnetic field has been investigated. Experimental results show that the dielectric constant reaches 104 at high temperature region, and the low temperature dielectric behavior confirms that the electrical transport behavior follows a variable-range-hopping (VRH) model. The dielectric behavior varies with the external magnetic field where the magnetic field induced phase transition of charge order (CO) is companied with the change of the dielectric behavior, indicating a magnetoelectric properties of the charge ordered compound of La1.67Sr0.33NiO4. Therefore, the coexistence of Ni3+ and Ni2+ ions makes the CO, which responds orderly at high temperature under the action of external magnetic field may contributed to the observed magnetodielectric behavior.

Field-Orientation Effect on Ferro-Quadrupole Order in PrTi2Al20

Ferro-quadrupole (FQ) order in the non-Kramers $\Gamma_3$ doublet system PrTi$_2$Al$_{20}$ has been investigated via angle-resolved measurements of the specific heat, rotational magnetocaloric effect, and entropy, under a rotating magnetic field within the $(1\bar{1}0)$ plane. The FQ transition occurring at 2 K is robust when the magnetic field $B$ is applied precisely along the $[111]$ direction. By contrast, the magnetic field of larger than 1 T tilted away from the $[111]$ direction sensitively changes the FQ transition to a crossover. The energy gap between the ground and first-excited states in the FQ order increases remarkably with the magnetic field in $B \parallel [001]$, but hardly depends on the magnetic-field strength, at least up to 5 T, in the field orientation between the $[111]$ and $[110]$ axes. These features can be reproduced by using a phenomenological model for FQ order assuming an anisotropic field-dependent interaction between quadrupoles, which has been recently proposed to explain the field-induced first-order phase transition in PrTi$_2$Al$_{20}$. The present study demonstrates the great potential of the field-angle-resolved measurements for evaluating possible scenarios for multipole orders.

Optical modulation studies of multiwall carbon nanotube dispersed in hydrogen bonded ferroelectric liquid crystal mixture for electro-optic devices

Structural, optical and electrical properties of multiwall carbon nanotubes (MWCNT) dispersed liquid crystalline (LC) mixture is extensively studied for electro-optic devices. A small amount of (0.1%) MWCNT is dispersed in cholesteryl stearate (CHS) and 4-dodecyloxybenzoic acid (12OBA) and its mixture is further characterized. Hydrogen bond between the mesogenic compounds are confirmed using FT-IR. Surface morphology and MWCNT dispersion in hydrogen bonded ferroelectric liquid crystal (HBFLC) mixture is established by SEM studies. Optical studies of the mixture using polarizing optical microscope (POM) is recognized by the induced smectic blue phase and smectic A* mesogenic phases. Transition temperatures and its corresponding enthalpy values of induced mesophases are analyzed by differential scanning calorimetry (DSC). An interesting observation of optical modulation in the present MWCNT dispersed HBFLC mixture is reported using dielectric studies. Textural modification with respect to external stimulus (bias voltage) in the present HBFLC mixture is reported. Further the field induced phase transitions and improved dielectric permittivity due to the dispersion of MWCNT is also reported.

Understanding the large strain behavior in the lead-free doped Bi1/2(Na0.78K0.22)1/2TiO3–BiMg1/2Ti1/2O3 (BNKT-BMT) piezoelectric system

The ternary solid solution Bi1/2(Na0.78K0.22)1/2TiO3-BiMg1/2Ti1/2O3 (BNKT-BMT) was investigated for high-strain actuator applications. This study of the BNKT-BMT system looked at the macroscopic properties as a function of BMT doping, temperature, and virgin vs poled states in order to gain new insights into the impact of quenched compositional disorder on non-ergodic to ergodic behavior in relaxor ferroelectrics. A gradual transition toward ergodic relaxor ferroelectric behavior was observed in the electric field induced polarization and strain of the BNKT-BMT system with an increase in concentration of BMT and an increase in temperature. BNKT-0%BMT exhibits a remarkable room temperature large-signal piezoelectric strain equivalent to an effective piezoelectric coefficient (d33*) >1000 pm/V at 5.5 kV/mm during the first virgin drive cycle due to the significant strain arising from an irreversible field induced phase transition characteristic of a non-ergodic relaxor ferroelectric. The maximum room temperature large-signal effective piezoelectric coefficient d33* observed for reversible bipolar cycling drive conditions was 685 pm/V at 5.5 kV/mm for BNKT-4%BMT. At elevated temperatures, compositions with reduced BMT exhibited superior d33* performance until a relative maximum d33* was reached and strain performance subsequently declined. This is interpreted in terms of competing strain mechanisms in relaxor ferroelectrics that vary with an increase in ergodicity of the system, as governed by factors such as composition and temperature. The work has implications for industrial actuator systems, such as those in inkjet printers.

Role of the spin anisotropy of the interchain interaction in weakly coupled antiferromagnetic Heisenberg chains**Project supported by the National Natural Science Foundation of China (Grant No. 11674392), the Ministry of Science and Technology of China, National Program on Key Research Project (Grant No. 2016YFA0300504), and the Research Funds of Remnin University of China (Grant No. 18XNLG24). R.Y. acknowledges the hospitality

In quasi-one-dimensional (q1D) quantum antiferromagnets, the complicated interplay of intrachain and interchain exchange couplings may give rise to rich phenomena. Motivated by recent progress on field-induced phase transitions in the q1D antiferromagnetic (AFM) compound YbAlO3, we study the phase diagram of spin-1/2 Heisenberg chains with Ising anisotropic interchain couplings under a longitudinal magnetic field via large-scale quantum Monte Carlo simulations, and investigate the role of the spin anisotropy of the interchain coupling on the ground state of the system. We find that the Ising anisotropy of the interchain coupling can significantly enhance the longitudinal spin correlations and drive the system to an incommensurate AFM phase at intermediate magnetic fields, which is understood as a longitudinal spin density wave (LSDW). With increasing field, the ground state changes to a canted AFM order with transverse spin correlations. We further provide a global phase diagram showing how the competition between the LSDW and the canted AFM states is tuned by the Ising anisotropy of the interchain coupling.

Phase diagram and quantum criticality of Heisenberg spin chains with Ising anisotropic interchain couplings

Motivated by recent progress on field-induced phase transitions in quasi-one-dimensional quantum antiferromagnets, we study the phase diagram of $S=1/2$ antiferromagnetic Heisenberg chains with Ising anisotropic interchain couplings under a longitudinal magnetic field via large-scale quantum Monte Carlo simulations. The interchain interactions is shown to enhance longitudinal spin correlations to stabilize an incommensurate longitudinal spin density wave order at low temperatures. With increasing field the ground state changes to a canted antiferromagnetic order until the magnetization fully saturates above a quantum critical point controlled by the $(3+2)$D XY universality. Increasing temperature in the quantum critical regime the system experiences a fascinating dimension crossover to a universal Tomonaga-Luttinger liquid. The calculated NMR relaxation rate $1/T_1$ indicates this Luttinger liquid behavior survives a broad field and temperature regime. Our results determine the global phase diagram and quantitative features of quantum criticality of a general model for quasi-one-dimensional spin chain compounds, and thus lay down a concrete ground to the study on these materials.

Microwave dynamics of the stoichiometric and bond-disordered anisotropic S=1 chain antiferromagnet NiCl2−4SC(NH2)2

We studied electron spin resonance in a quantum magnet NiCl2-4SC(NH2)2, demonstrating a field-induced quantum phase transition from a quantum-disordered phase to an antiferromagnet. We observe two branches of the antiferromagnetic resonance of the ordered phase, one of them has a gap and the other is a Goldstone mode with zero frequency at a magnetic field along the four-fold axis. This zero frequency mode acquires a gap at a small tilting of the magnetic field with respect to this direction. The upper gap was found to be reduced in the doped compound Ni(Cl(1-x)Br(x))2-4SC(NH2)2 with $x=0.21$. This reduction is unexpected because of the previously reported rise of the main exchange constant in a doped compound. Further, a nonresonant diamagnetic susceptibility $\chi^{\prime}$ was found for the ordered phase in a wide frequency range above the quasi-Goldstone mode. This dynamic diamagnetism is as large as the dynamic susceptibility of the paramagnetic resonance. We speculate that it originates from a two-magnon absorption band of low-frequency dispersive magnon branch.

Scaling of the magnetic entropy change in chiral helimagnetic YbNi3Al9

Generally, magnetic anisotropy is a common feature of a layered magnetic material, the exploration of which plays a key role in understanding the intrinsic magnetic couplings. In this work, we have studied the field-induced magnetic transitions for layered YbNi3Al9 as the external magnetic field is applied perpendicularly () and parallel (H//c) to the c-axis. We find that two independent universal curves of magnetic entropy change [] can be fitted out for and H//c, respectively. According to the universality principle of scaling, the extra magnetic entropy changes ( and ) caused by the field-induced magnetic phase transitions can be obtained for and H//c. The two-dimensional plots as functions of field and temperature are constructed, which clearly reveal the evolutions of the magnetic entropy changes resulted from the two different field-induced magnetic phase transitions. It is suggested that the for with the maximum at (3.2 K, 4.1 kOe) originates from a field-modulated helicoidal spin-texture. However, the for H//c with the maximum at (3.4 K, 13.8 kOe) stems from a field-induced canted antiferromagnetic state.

Comparative study of piezoelectric response and energy-storage performance in normal ferroelectric, antiferroelectric and relaxor-ferroelectric thin films

The energy-storage performance and piezoelectric properties were determined for epitaxial antiferroelectric (AFE) PbZrO3 (PZ), ferroelectric (FE) PbZr0.52Ti0.48O3 (PZT), and relaxor ferroelectric (RFE) Pb0.9La0.1Zr0.52Ti0.48O3 (PLZT) thin films that were deposited on to SrTiO3 buffered Si substrates. The films were investigated by directly measuring the polarization hysteresis loops and piezoelectric strain curves. The square polarization loop with a high remanent polarization and a large piezoelectric coefficient obtained in PZT thin films allow them to be useful for various applications in ferroelectric field effect transistors and/or in MEMS actuators. Meanwhile, there is a jump of about 0.9% in the strain curve of PZ thin films around the field-induced AFE-FE phase transition, which is useful in digital displacement transducers due to a good ON/OFF strain state. The large recoverable energy-storage density, excellent energy-storage efficiency, and low strain hysteresis due to a slim hysteresis loop combine to make PLZT thin films as a potential candidate for a broad range of applications from energy storage to nano-positioning precision systems.

Electric-field-induced phase transition in 2D layered perovskite (BA)2PbI4 microplate crystals

Two-dimensional (2D) lead halide perovskite materials are solution-processable semiconductor materials, which would find promising applications in optoelectronic devices. The fundamental understanding of the structural phase transition in two-dimensional perovskites is of great importance for fully exploiting their potential applications in electronic and optoelectronic devices. Here, we report on how the external electric field affects the structural phase transition in 2D perovskite (BA)2PbI4 microplates via temperature-dependent photoluminescence spectroscopy. A high-temperature phase and a low-temperature phase can coexist in a wider range of temperatures. The external electric field would enhance the phase transition to the dominant phase depending on the surrounding temperature. This field-induced phase transition might be ascribed to the release of strain in the perovskite microplate induced by the applied electric field, leading to the change in the structural phase transition temperature. Our findings are of great significance not only to the fundamental understanding of phase transition but also to the design and optimization of two-dimensional perovskite based electronic and optoelectronic devices.

Fabrication, structural and dielectric property of lead-free perovskite silver niobate ceramics

Dielectric capacitors with high recoverable energy density are in high demand for their application in electrical and electronic systems. Among lead-free dielectric materials, silver niobate (AgNbO3) has attracted growing interest due to its superior energy storage density at room temperature. The field-induced phase transition from antiferroelectric (AFE) phase to ferroelectric (FE) phase contributes to its large energy density. In this work, pure perovskite silver niobate ceramics were fabricated in an oxygen atmosphere by the solid-state reaction technique. The Pbcm orthorhombic phase of AgNbO3 was closely observed using the Rietveld refinement method to provide explanation for the origin of high spontaneous polarization within a unit cell. Local structural analysis via piezoelectric force microscopy revealed the existence of ferroelectric nano domains, which may contribute to the high energy storage efficiency (η = 99.9926%) in AgNbO3 at low electric fields. The phase transitions of AgNbO3 were also investigated via the dependence of the dielectric permittivity (ε′ and ε″) and loss angle tangent (tanδ) on temperatures, providing insights into the further modification of AgNbO3.