Field-induced Phase Transition Research Articles

Giant magnetocaloric effect of Ni-Co-Mn-Ti all-d Heusler alloys in high magnetic fields

Ni-Co-Mn-Ti all-d Heusler alloys are attracting considerable attention for solid-state caloric cooling applications due to their promising combination of excellent caloric and mechanical properties. Here, we report on the maximum attainable magnetocaloric effect in Ni37Co13Mn34.5Ti15.5, which shows a first-order magnetostructural martensitic transformation around room temperature. Heat capacity measurements reveal a giant transition entropy change of 43.5J(kgK)−1 and are utilized to estimate the magnetocaloric effect as well as the magnetic fields required to saturate it in isothermal and adiabatic conditions. Confirming the results based on this approach, we achieve maximum isothermal entropy changes and directly measured adiabatic temperature changes of 37.8J(kgK)−1 and −20.2K, respectively. Thus, the herein reported maximum attainable magnetocaloric effect outperforms classical Ni-Mn-based Heusler alloys, such as Ni(-Co)-Mn-In. Especially the saturated adiabatic temperature change surpasses all previously published values of magnetic field-induced first-order phase transitions measured around room temperature in pulsed magnetic fields in recent years. Thereby, we demonstrate that Ni(-Co)-Mn-Ti Heusler alloys are particularly suitable for the application of sufficiently large external stimuli to fully induce the phase transition and exploit their intrinsically large caloric effect.

Revealing the role of B-site cations in the antiferroelectricity of NaNbO3-based perovskites

The promising prospects of antiferroelectric perovskite oxides in the realm of energy storage applications hinge on the unique field-induced phase transitions. Once the transition is triggered by the application of an electric field, characteristic double polarization loops appear. However, NaNbO3-based materials that exhibit a reversible phase transition are still rare, which hinders the practical applications of lead-free antiferroelectrics. Here, the impact of materials chemistry on the competition between antiferroelectric and ferroelectric states is demonstrated in a series of NaNbO3-based solid solutions with varying perovskite B-site cations, while the A-site is fixed as strontium. The crystal structure is analyzed on the basis of Rietveld refinement of high-energy X-ray diffraction data. The phase transition behavior as well as the antiferroelectric and ferroelectric properties are probed by a series of electrical measurements. The antiferroelectric phase is universally observed for all investigated materials in the virgin state. The SrTiO3-substituted system shows an irreversible phase transition similar to that of pure NaNbO3. In contrast, double polarization hysteresis loops are observed in the SrHfO3-, SrZrO3-, and SrSnO3-substituted systems. It is confirmed that compounds that can reduce the tolerance factor of the system contribute to the stabilization of the antiferroelectric order, while those that can reduce the electronegativity difference lead to more pronounced double loops. The competition between antiferroelectricity and ferroelectricity is linked to the competition between covalent and ionic bonding in perovskites.

Magnetic control of Weyl nodes and wave packets in three-dimensional warped semimetals

We investigate the topological phase transitions driven by band warping, λ, and a transverse magnetic field, B, for three-dimensional Weyl semimetals. First, we use the Chern number as a mathematical tool to derive the topological λ×B phase diagram. Next, we associate each of the topological sectors to a given angular momentum state of a rotating wave packet. Then we show how the position of the Weyl nodes can be manipulated by a transverse external magnetic field that ultimately quenches the wave packet rotation, first partially and then completely, thus resulting in a sequence of field-induced topological phase transitions. Finally, we calculate the current-induced magnetization and the anomalous Hall conductivity of a prototypical warped Weyl material. Both observables reflect the topological transitions associated with the wave packet rotation and can help to identify the elusive 3D quantum anomalous Hall effect in three-dimensional, warped Weyl materials. Published by the American Physical Society 2024

Manipulation of anisotropic Zhang-Rice exciton in NiPS3 by magnetic field

The effect of external magnetic fields on the behavior of the Zhang-Rice exciton in NiPS3, which captures the physics of spin-orbital entanglement in 2D XY-type antiferromagnets, remains unclear. This study presents systematic study of angle-resolved and polarization-resolved magneto-optical photoluminescence spectra of NiPS3 in the Voigt geometry. We observed highly anisotropic, non-linear Zeeman splitting and polarization rotation of the Zhang-Rice exciton, which depends on the direction and intensity of the magnetic field and can be attributed to the spin-orbital coupling and field-induced spin reorientation. Furthermore, above the critical magnetic field, we detected additional splitting of the exciton peaks, indicating the coexistence of various orientations of Néel vector. This study characterizes orbital change of Zhang-Rice exciton and field-induced spin-reorientation phase transitions in a 2D hexagonal XY-type antiferromagnet, and it further demonstrates the continuous manipulation of the spin and polarization of the Zhang-Rice exciton.

Spin-flop phase transitions in vdW antiferromagnet MnPSe3

Two-dimensional (2D) van der Waal (vdW) magnets are gaining significance in exploring fundamental condensed matter physics and developing cutting-edge technologies. Here, we report the structural and magnetic properties of the antiferromagnetic semiconductor MnPSe3 crystal. Intriguing magnetic behaviors and the strong anisotropy of the bulk crystal have been investigated through temperature-dependent magnetization studies along with the observation of Néel temperature at TN=70±2 K. At temperatures below TN, the bulk MnPSe3 exhibits field-induced spin-flop phase transitions with a spin-flop field (HSF) of nearly 8 kOe at 5 K. These transitions are evidenced from isothermal magnetization measurements conducted at low temperatures. Moreover, temperature-dependent enhancement in HSF was also studied. Our findings motivate the exploration of intrinsic magnetic interactions in 2D MnPSe3 and incorporating it into functional vdW heterostructures and devices.

Observation of competing interactions and field-induced ferromagnetism in noncentrosymmetric cubic Nd3Te4 lattice

Unconventional magnetism is key to advancement in a variety of spintronic applications and thus needs to be explored in new materials. Here, we report the in-depth magnetic studies of noncentrosymmetric Nd3Te4 and findings support the existence of Dzyaloshinskii-Moriya interaction in addition to symmetric exchange interaction among the moments. The large magnetic irreversibility with negative magnetization in M(T) data and associated first-order magnetic transition in isothermal magnetization data suggest the competing interactions resulting in multiple magnetic phases. The gradual evolution of magnetic texture has been probed by changes in the magnetization entropy having interesting characteristics like the inverse magnetocaloric effect. Most importantly, we have probed the existing nontrivial magnetic phase under a low applied magnetic field by ac-χ(T, H) and dc magnetization (M − H) data, having the same critical field in both measurements. The existence of multiple magnetic phases which are interconnected through first-order field-induced magnetic phase transitions have been probed at low field. The transition from paramagnetic to field-induced state for larger applied fields follows a second-order.

Advancing piezoelectric properties of barium titanate ceramic through AC + DC field poling over Curie temperature

The significance of increased domain nucleation sites from smaller grain size (GS) of barium titanate (BT) ceramics on piezoelectric properties was analyzed for different types of poling, including conventional DC poling, modified DC poling, and AC plus DC poling, conducted at different poling temperatures. The AC plus DC poling conducted at 1.5 °C above the Curie temperature (T C) showed the highest piezoelectric constant (d 33) of 528 pC/N, with an average domain size of 100 nm observed after poling. The d 33 improvement was attributed to smaller domain size formation from field-induced phase transitions and homogenous distribution of point defects achieved by the AC field. Comparative analysis with larger grain BT ceramics under AC plus DC poling suggests that defects and volume fraction of grain boundaries in BT ceramics could have an effect on domain sizes.

Large Nonhysteretic Volume Magnetostriction in a Strong and Ductile High-Entropy Alloy.

Rapid development of smart technologies poses a big challenge for magnetostrictive materials, which should not only permit isotropic and hysteresis-free actuation (i.e., nonhysteretic volume change) in magnetic fields, but also have high strength and high ductility. Unfortunately, the magnetostriction from self-assembly of ferromagnetic domains is volume-conserving; the volume magnetostriction from field-induced first-order phase transition has large intrinsic hysteresis; and most prototype magnetostrictive materials are intrinsically brittle. Here, a magnetic high-entropy alloy (HEA) Fe35Co35Al10Cr10Ni10 is reported that can rectify these challenges, exhibiting an unprecedented combination of large nonhysteretic volume magnetostriction, high tensile strength and large elongation strain, over a wide working temperature range from room temperature down to 100 K. Its exceptional properties stem from a dual-phase microstructure, where the face-centered cubic (FCC) matrix phase with nanoscale compositional and structural fluctuations can enable a magnetic-field-induced transition from low-spin small-volume state to high-spin large-volume state, and the ordered body-centered cubic (BCC) B2 phase contributes to mechanical strengthening. The present findings may provide insights into designing unconventional and technologically important magnetostrictive materials.

In situ X-ray diffraction evidence of field-induced transitions in a PbHfO3 single crystal

Antiferroelectric (AFE) materials are interesting due to recent discoveries of new prospective applications, although the mechanisms of the phase transitions that are at the heart of these applications remain incompletely understood. This work is devoted to the study of a single crystal of a model AFE, lead hafnate, by X-ray diffraction with in situ application of an electric field to trigger the transition to a polar phase. Two consecutive experiments were carried out on a 35 µm thick plate with [110] surface normal orientation over a field range from 0 to 330 kV cm−1 and back. A sharp drop in the intensity of R- and Σ-type reflections around 225 kV cm−1 was registered, with almost complete disappearance after 250 kV cm−1. This is compatible with a field-induced phase transition from the AFE to the R3m polar phase, which was suggested earlier on the basis of non-diffraction characterizations. X-ray diffraction reveals that the AFE domains with displacements parallel to the field direction react much more smoothly to the field, gradually reducing the AFE order at very small fields instead of holding it almost constant up to the critical field value, which is naturally expected. This expectation is fulfilled for domains with other orientations, but only for the first switching cycle; in the second switching cycle the AFE order already shows a notable decrease at subcritical fields. It is suggested that these observations could be linked with the antiphase domain wall population being affected by the field, which is consistent with the observation of diffuse rods between the Γ and Σ points. Another remarkable observation is the much smoother recovery of the AFE phase compared with its sharp disappearance at the critical field.

PYN-based antiferroelectric ceramics with superior energy storage performance within an ultra-wide temperature range

Antiferroelectric (AFE) ceramics are known for their rich field-induced phase transitions, which mainly contribute to their superior energy storage performance. However, the phase transitions instability caused by high temperature often limits its application scenarios. Developing AFE ceramics with high energy storage properties and wide application temperature ranges is challenging. Here, considering the B-site ordering characteristics of Pb(Yb0.5Nb0.5)O3, we propose a simple approach for introducing A-site distortion and adjusting B-site ordering to confront these challenges. In our Fe3+/Sr2+co-doping system, we realized an ultra-wide temperature range of 25–200 °C, within which the recoverable storage density was considerable: 8.48–13.39 J cm−3. In this interval, the discharge energy density could reach 6.15–9.67J cm−3, and the discharge current density and discharge power density were 755.09–1667.36 A cm−2 and 207.65–500.21 MW cm−3, respectively. The obtained high-temperature energy storage performance was superior to that of existing energy storage ceramics or polymer films. The introduction of A-site distortion improves the stability of AFE phase, the decrease in B-site ordering suppresses the remanent polarization and delays change in structural symmetry with temperature. This study forms a basis for further applications of dielectric capacitors and signifies the development of wide-temperature-range energy storage devices.

Field-induced effects and ferroelectric critical endpoint in (K0.95Li0.05)(Nb1–x Ta x )O3 single crystals

Dielectric permittivities under dc biasing fields in the temperature range between –169 °C and 75 °C have been investigated in (K0.95Li0.05)(Nb1–x Ta x )O3 (KLNT–x, x = 71% and 74%). Field-induced ferroelectric phase transitions in KLNT–x have been clarified in the dc field applied along the [001] c direction (in the cubic coordinate). The ferroelectric critical endpoints in KLNT–71% and KLNT–74% have been determined to be 43.5 °C, 3.0 kV cm−1, and 30.3 °C, 2.0 kV cm−1, respectively. The tricritical point at which the first-order phase transition changes to the second-order phase transition has been estimated at 10.4 °C and x = 77.4% in the temperature–concentration phase diagram. The field-induced phase transitions and dielectric tunabilities have been discussed on the basis of the Landau-type free energy density.

Regulating the switching electric field and energy-storage performance in antiferroelectric ceramics via heterogeneous laminated engineering

Antiferroelectric (AFE) ceramics with near-zero remanent polarization originating from unique electric field-induced antiferroelectric-ferroelectric phase transition are of great importance for the application in the energy-storage devices. However, achieving the most widely optimized switching electric field and energy-storage performance of antiferroelectric ceramics has predominantly relied on A/B-site ion doping strategies, often accomplished through a series of experimental and analytical works. In this context, we propose a novel strategy of heterogeneous laminated engineering as a substitute for A/B-site ion doping. This approach allows for a more intuitive regulation of the switching electric field and energy-storage performance in antiferroelectric ceramics without the need for complicated workload. Namely, the ferroelectric Pb0.99(Nb0.9Ta0.1)0.2(Zr0.9Sn0.1)0.8O3 (PNTZS) and antiferroelectric (Pb0.875La0.05Sr0.05) (Zr0.7Sn0.3)O3 (PLSZS) were layer-by-layer laminated using a tape-casting technique. All heterogeneous laminated ceramics exhibit antiferroelectric characteristics, and the magnitude of the switching electric field can be controlled by regulating the ratio between PNTZS and PLSZS. Furthermore, the finite element simulation revealed differences in the local electric fields between PNTZS and PLSZS in heterogeneous laminated ceramics, resulting in a win-win situation for both polarization and the breakdown strength. A large recoverable energy density of 11.2 J cm−3 with ultrahigh energy efficiency of 94.2 % can be obtained under 56 kV mm−1. Moreover, the energy storage performance shows no obvious deterioration in a broad frequency range (1–100 Hz) and temperature range (25–120 °C). Particularly, the outstanding discharge properties with a large discharge energy density of 7.1 J cm−3 and a high power density of 263.7 MW cm−3 show great potential for energy-storage applications. To conclude, a new strategy is opened up herein for designing antiferroelectric energy storage materials, showing the great application potential in the pulse power devices.

Numerical simulation of electric field-induced phase transition evolution and boiling characteristics in the evaporative cooling medium C6F12O

Phase change cooling technology offers high cooling efficiency, safety, and reliability, representing a novel approach to achieving efficient heat dissipation for high-power and large-capacity electrical equipment. The formulation of the cooling medium is pivotal to phase change cooling technology. However, current media exhibit compatibility, stability, economy, and environmental friendliness deficiencies. Consideration could be given to implementing the C6F12O medium due to its superior overall performance and ability to meet the latent heat requirements in phase change cooling equipment. This paper employs a numerical simulation approach that combines the phase field method based on the Cahn-Hilliard equation with the theory of electrohydrodynamics. It investigates the impact of temperature, electric field intensity, and electric field direction on the evolution of bubble motion and the boiling state of the C6F12O medium, considering the interaction of electric-fluid-heat-phase fields. Numerical results indicate that the system undergoes initial nucleate boiling, nucleate boiling, and film boiling stages at T = 330–335 K, T = 335–350 K, and T ⩾ 355 K, respectively. The introduction of an appropriate electric field can enhance the motion evolution of C6F12O bubbles. However, attention must be paid to the formation of bubble channels under high field strength to prevent potential decreases in insulation performance. An inhomogeneous electric field in the vertical direction proves more effective in improving the bubble release rate compared to a uniform electric field. To some extent, an inhomogeneous electric field in the horizontal direction can prevent the mass accumulation of bubbles in regions of high field intensity. This research has the potential to offer theoretical guidance for the engineering application of the C6F12O phase change cooling medium.

Magnetoresistance and magnetic field-induced phase transition in two-dimensional antiferromagnet Fe1/3NbS2

We perform systematic studies on the magnetic and magnetotransport properties of Fe1/3NbS2 single crystal. Results show that Fe1/3NbS2 is an antiferromagnet with strong perpendicular magnetocrystalline anisotropy even in the paramagnetic state. The Fe1/3NbS2 nanoplate exhibits exotic magnetotransport characteristics with variation of temperature and magnetic field in the vicinity of Néel temperature. The temperature dependence of resistivity indicates that the magnetic field has a substantial effect on the Néel order of Fe1/3NbS2, and an intermediate phase occurs before the sample enters into the antiferromagnetic state. It is the field- or temperature-induced antiferromagnetic–intermediate phase and intermediate phase–paramagnetic phase transitions that lead to the novel magnetotransport characteristics in the vicinity of Néel temperature. The findings in this work will promote future studies based on two-dimensional antiferromagnetic spintronics.

Ultra-high strain in Bi0.5(Na0.41K0.09)TiO3 Pb-free piezoelectric ceramics modified by Sr(Hf0.5Sb0.4)O3

The lead-free piezoelectric ceramics used in piezoelectric actuators have attracted extensive attention owing to their substantial electric-field-induced strain. In this study, The (1-x)Bi0.5(Na0.41K0.09)TiO3-xSr(Hf0.5Sb0.4)O3 (BNKT-xSHS) piezoelectric ceramics were synthesized using the conventional solid-state reaction method. The impact of SHS substitution on the microstructure and electrical properties was systematically explored. Among them, the BNKT-0.015SHS sample, featuring ergodic relaxor states, demonstrates a high piezoelectric strain coefficient (d33*) of 785 p.m./V under a low electric field of 50 kV/cm(Strain = 0.392 %). It exhibits a repeatable strain value of 0.47 % under an 80 kV/cm electric field(d33* = 590 p.m./V). Moreover, the strain values remain around 0.4 % between room temperature and 100 °C, with variations within 90 %. The heightened repeatable strain response is considered to be linked to the electric field-induced reversible phase transition occurring within the ergodic relaxor state. The higher strain temperature stability is ascribed to the coexistence of quadrilateral polar nanoregions and rhombic polydomain nanoregions. This study provides an effective example for achieving significant strain responses, presenting a feasible candidate material for applications in piezoelectric actuators.

Achieving large negative electrocaloric effect in AgNbO3-based antiferroelectric ceramics based on dipole disordering

The electrocaloric effect (ECE) is considered as an environmentally friendly refrigeration technology, which can be used to replace vapor compression refrigeration. Lead-free antiferroelectric (AFE) ceramics are promising electrocaloric materials because of large saturation polarization and polarization change with temperature, which can generate large positive or negative ECE. In this work, the lead-free Ag(Nb1-0.8xHfx)O3 (x = 0, 0.001 and 0.003) AFE ceramics are fabricated through a conventional solid-state reaction method which shows a decreased the phase transition temperature of M1 - M2 toward room temperature (RT), and a large negative ECE (ΔT = −2.3 K under 130 kV cm−1) is obtained near the ambient temperature by using an indirect measurement in ANH0.001 AFE ceramic. The large negative ECE behavior is ascribed to dipole disordering (i.e. the anti-parallel dipoles are broken and gradually becomes disordered under an external electric field) resulting from the field-induced phase transition under a modest electric field. This work shows that AgNbO3-based AFE ceramics could be used in the refrigeration devices as an electrocaloric material.

Phenomenological analysis of positive and negative electrocaloric effects in Rochelle salt

Ferroelectrics exhibiting both positive and negative electrocaloric effects stand out as promising materials for achieving high-efficiency solid-state refrigeration. The phase transition is acknowledged as a crucial factor in designing such materials. This study investigates the electrocaloric behavior and its correlation with phase transitions in Rochelle salt single crystal using Landau thermodynamic theory. Analysis of free energy density, ferroelectric, and dielectric data uncovers a complex temperature-dependent phase transition sequence of paraelectric–ferroelectric–paraelectric. This imparts Rochelle salt single crystal with intriguing field-induced phase transition behaviors and electrocaloric responses. Pronounced positive and negative electrocaloric effects are, respectively, observed near the high-temperature and low-temperature Curie point. The opposite sign of entropy differences between the ferroelectric and the two paraelectric phases is identified as the origin of the difference in electrocaloric response. These findings not only enhance our understanding of the electrocaloric effect but also provide a design solution for materials with the coexistence of positive and negative electrocaloric effects.

Polarization fatigue mechanism of laminated hafnium zirconium oxide ferroelectric thin films

Laminated HfO2-based ferroelectric thin films (FE-HfO2) have offered unexpected opportunities to implement the high-density ferroelectric memory and on chip piezoelectric or pyroelectric devices. But the polarization fatigue performance is poor and the underlying mechanism is unknown. In this work, we comprehensively investigate the polarization fatigue behaviors of Hf0.5Zr0.5O2(HZO)/Al2O3/HZO laminated thin films. Several possible mechanisms for the fatigue performances are discussed in detail. On basis of the analysis of micro-structures and domain switching dynamics before and after fatigue, we confirm that domain wall pinning phenomenon exists in the fatigued laminated HZO, without field-induced phase transition as well as thickness and chemical properties changes of interfacial layers. Moreover, we discover by a pulse measurement method that domain wall pinning induced by the increase of Al2O3/HZO interface trap charge is responsible for the fatigue performances of the laminated films. This work will provide useful guidance for designing high-reliability laminated FE-HfO2, and contribute to understand the physical mechanisms of FE-HfO2.

An enhanced strain response in micrometer-thick BNT-ST thin films

Lead-free Bi0.5Na0.5TiO3-SrTiO3 (BNT-ST) thin films with various thicknesses were deposited on the Pt(111)/Ti/SiO2/Si(100) substrates employing a sol-gel technique with a two-step annealing process. Despite the variations in thickness, the films exhibited a consistent polycrystalline structure, evidenced by identical diffraction peaks, albeit with differences in intensity. An imprint became evident in micro-thick films, increasing with film thickness. Also, the emergence of self-polarization was observed in thicker films detected by piezoresponse force microscopy. Noteworthy is the pronounced influence of film thickness on strain response, with the 1.38 μm-thick films demonstrating a large strain of 1.18%. The outstanding strain response can be attributed to the notable contribution of electric field-induced phase transition and polarization dynamics. This work provides a promising potential application of micrometer-thick BNT-ST thin films in advanced actuator devices.

Magnetic field-induced phase transition in spinor exciton-polaritons condensate

We theoretically study the magnetic phase transition of condensed exciton-polariton microcavities in an applied magnetic field. When the magnetic field is strong, all polariton spins are polarized parallel to the magnetic field as usual. On the contrary, in the weak magnetic-field region, the polariton polarization degree is negative, namely, anti-parallel to the magnetic field. For a strong magnetic field, the magnetic phase of the polaritons arises and leads to a paramagnetic, while around a weak magnetic field, with zero exciton–photon detunings, and weak Rabi splitting the spin polarization of the polaritons leads to a diamagnetic. Thus, magneto-polariton phase transition polarization originates from the competition between the polariton Zeeman effect and polariton–polariton interactions. Moreover, the polariton polarization strongly depends on the exciton–photon detuning and Rabi splitting and has a large negative value as they are both small. At last, we compare our theoretical results with the experiments and find they match each other very well.