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The characteristic size of the magnetocaloric materials in magnetic refrigerators, thermomagnetic regenerators and energy harvesters is usually down to micrometer and nanometer length scales, which provides the largest possible contact surface area to the heat transfer liquid. Therefore, it is pivotal to investigate the structural, magnetic and magnetocaloric properties of magnetocaloric materials at micrometer and nanometer length scales. In the present study, we have successfully fabricated MnCoGe-based thin films using the pulsed laser deposition (PLD) technique. The as-deposited film shows a dense surface, homogeneous chemical distribution and a preferred orientation along the c -axis of the hexagonal Ni 2 In-type structure. In-situ temperature-dependent X-ray diffraction measurements on the as-deposited films reveal an irreversible structural degradation above 300 °C due to the considerable evaporation of the Mn atoms, which causes the formation of microscale pores in the films. The thermomagnetic behavior of the film annealed at 250 °C displays a reversible second-order ferromagnetic transition of the hexagonal phase at Curie temperature T C = 275 K, and a first-order hexagonal-orthorhombic structural transition below 200 K. The decoupling of the magnetic and structural transitions brings reversible magnetocaloric effect with the entropy change ΔS values of 2.5 J/(kgK) and the refrigeration capacity reaching 89 J/kg in Δμ 0 H = 5 T, which are comparable to other reported magnetocaloric thin films. Moreover, antiferromagnetic coupling in the low-temperature orthorhombic phase was observed, which has rarely been reported in the MnCoGe-based bulk alloys. The different magnetic ground states between the thin film and the bulk alloys may be originated from the strain effect imposed by the Al 2 O 3 substrate. Consequently, this work not only provides insights into the structural, magnetic and magnetocaloric properties of the MnCoGe-based alloys at a nanometer length scale, but also offers a new idea for tailoring the multifunctional properties for this material family. [ABSTRACT FROM AUTHOR]

In the present work, we have demonstrated that the coupling and decoupling between the magnetic and structural transitions can be manipulated by the partial replacement of the Mn by Zr in the MnCoGe alloys. Energy-dispersive spectroscopy analyses reveal a homogeneous distribution of the Zr atoms throughout the samples. The differential scanning calorimetry and X-ray diffraction results reveal a decrease in the structural transition temperature Tt with an increase in the Zr content. A strong magneto-structural coupling can be realized in the Mn1−xZrx CoGe with 0.04 ≤ x ≤ 0.07, where the Tt is lowered to the temperature range between the Curie temperatures of the orthorhombic and hexagonal phases. The magneto-structural transition is accompanied with significant changes in the interatomic distances between the magnetic atoms, which strongly influence both the magnetic exchange interactions and the chemical bonding. As a result, a coincidence of the magnetic and structural transitions is observed, which brings a giant magnetocaloric effect due to the contributions from both the lattice and the magnetic entropy changes. [ABSTRACT FROM AUTHOR]

Abstract: Single-phase broad-band red-emitting Ca3Si2O7:Eu2+ phosphors, with photoluminescence features that qualify them as candidates for white light-emitting diodes applications, were successfully synthesized via a modified solid-state reaction method that employed H3BO3 as a flux. The phosphors produced have an intense broad red emission band, with a peak at 603nm, a full width at half maximum of 110nm, and color coordinates of (0.550, 0.438). Concentration quenching occurred at 0.01mol Eu2+. The discussion of the results shows that Eu2+ ions should be accommodated at the Ca-sites of the lattice, dipole–dipole interactions should predominantly govern the energy transfer mechanism among them, and the critical distance between them is ∼31Å. [Copyright &y& Elsevier]

• Pure and homogeneous MnSi is obtained via arc melting and post-annealing. • MnSi polycrystals show typical magnetic transitions as observed in single crystals. • Magnetic skyrmions can be identified in polycrystalline MnSi using magnetometry. We employed x-ray diffractometer, electron microscope and magnetometer to study the structure and magnetic properties of polycrystalline MnSi. Pure and homogeneous MnSi phase can be obtained in a certain composition range. Intriguingly, our magnetic measurements indicate that the polycrystalline MnSi shows typical magnetic phase transitions as single crystals. The magnetic transformations between helical, conical, skyrmion and field-polarized states can be well detected in the field-dependent susceptibility curves. The similar magnetic behaviors observed for polycrystalline and single crystals make magnetometry an effective and straightforward route to identify skyrmions, especially useful for the materials that are hard to prepare single crystals or epitaxial thin films. [ABSTRACT FROM AUTHOR]

For achieving more functionalities of perovskite manganese oxides film, an epitaxial La 0.8 Sr 0.2 MnO 3 (LSMO) film was deposited on a flexible substrate (mica) by pulsed laser deposition. The film shows a paramagnetic-ferromagnetic (PM-FM) phase transition at 134 K together with metal-insulator transition (MIT) at 149 K. The measurement of hysteresis loop indicates that the easy-magnetization axis lied in film plane. The transport behavior can be fitted well with the small polaron model, giving out the activation energy E hop = 176.9 meV. Different from the common anisotropic magnetoresistance (AMR) in manganite film, an isotropic magnetoresistance (IMR) effect was observed in LSMO film and the relatively small thickness of LSMO film (∼ 50 nm) is a major reason for it. After the cyclic flexural bending for 1.0 × 104 times, we found the magnetic properties of LSMO film were improved. Micromagnetic detection shows that the activation energy for polaron hopping (E a = 144.7 meV) remarkably decreases by the cyclic flexural bending process. We suggested that the inhomogeneous/incompact part located at the zone of neighbouring domains become uniform and tight after circulating bending, which facilitates the rotation of domains and the polarons hopping so that the magnetic and electronic performance are enhanced. • A flexible pervoskite manganite film has been fabricated by PLD. • The film shows an exchanged polaron interactions in transport behavior. • An isotropic magnetoresistance effect was observed in film. • The magnetization and electronic transport property have been promoted after the cycling bending. [ABSTRACT FROM AUTHOR]

In an effort to explore new electronic devices with multiple functionalities, there are numerous studies of depositing perovskite oxides on flexible substrates to replace rigid silicon‐based wafer in device applications. In this study, the growth of pseudocubic SrRuO3 single‐crystal thin film on a transparent and flexible muscovite is established. The experimental results confirm that the Curie temperature TC and the magnetic properties can be effectively tuned via the mechanical strain due to the facilitation of flexible substrate. It is found that the tensile strain increases while the compressive strain decreases the spontaneous magnetization for the thin film suffering the same ±0.24% strain. Based on the study of critical behavior, the critical exponents β = 0.543(19) and γ = 1.262(1) with the critical temperature TC = 159.04(5) K and TC = 159.10 K, respectively, are obtained by the modified Arrott plot. The set of critical exponents matches well with Widom scaling relation and the scaling equation, indicating these critical exponents are intrinsic for SrRuO3 thin films. Moreover, it is achieved that the SrRuO3 thin films exhibit a long‐range interaction coupled with 3D‐Heisenberg type. [ABSTRACT FROM AUTHOR]

[Display omitted] • (1) Both the epitaxial strain and the content of surface-adsorbed oxygen affect the heterostructures' photoconductivity. • (2) Mechanical strain generated by bending the fluorphlogopite substrate also has a modulating effect on the photoresponse of the flexible heterostructures. • (3) The heterostructure maintains a good photoresponse after 105 bending cycles without essentially weakening, indicating a superior mechanical durability and stability. The research of high-speed photodetector and high-speed optical receiver garners significant attention due to their indispensable properties in many fields including high-temperature event monitoring, security, and ad hoc network wireless communication. Inorganic perovskite oxides LaCoO 3 films showcase an extensive prospect in this area owing to their remarkable photoconductive effect. Up to present, however, LaCoO 3 films are mostly grown on rigid instead of flexible substrates, greatly limiting their applications to wearable optoelectronic sensors. In this work, we fabricated some flexible LaCoO 3 thin films to study their photoresponse. By inserting SrTiO 3 and BaTiO 3 as buffer layers, we find that LaCoO 3 thin films could epitaxially grow on the fluorphlogopite surface and show a stable photoresponse to visible-light. Nevertheless, we also found that the epitaxial strain and the content of surface-adsorbed oxygen could impact the photoconductivity. The mechanical strain generated by bending the fluorphlogopite substrate has been confirmed to has a tunable effect on the photoresponse. Moreover, with the fatigue tests of 105 bending cycles, the flexible LaCoO 3 thin films maintain a good photoresponse without any essentially weakening, proving a superior mechanical durability and stability. This work not only indicates the feasibility of the LaCoO 3 films applied for flexible photodetectors but also opens a path for other perovskite films applications for flexible substrate. [ABSTRACT FROM AUTHOR]

A multicolour LED is a miniaturized, long-lasting, and easy-to-achieve colour adjustable emission light source. It is widely used in outdoor displays and room lighting fields. However, the increase in the cost and the decrease in luminous efficiency when adjusting lighting colours have constrained the development of multicolour LEDs. In this study, we initially designed a phosphor conversion pixel array through optical simulation and then prepared the phosphor conversion pixel arrays with different layouts using a semi-cured template method. Finally, we packaged the phosphor conversion pixel array with the blue LED array as a remote phosphor LED. The measurement of the luminous performance indicated that the colour gamut of multicolour LEDs was included in the simulated colour gamut, and the colour of the light was consistent with the design guidelines. Notably, the multicolour LED emission efficiency packaged with a phosphor conversion pixel array could reach 125 lm/W, and the hexagonal phosphor conversion pixel array had better emission performance than the square phosphor conversion pixel array. • Based on the Monte Carlo principle, multicolour LEDs composed of array phosphor-converted film and blue-LED chip are designed. • Phosphor-converted pixel arrays are prepared by semi-cured template method with high moulding quality. • By comparing the experimental and simulation results, colour-tuneable characteristics of the multicolour LEDs is verified. • The luminous efficiency of multicolour LEDs reach up to 125.0 lm/W and changing pixel can reduce the secondary reabsorption of fluorescence. [ABSTRACT FROM AUTHOR]

Apart from the impact of different substrates on epitaxial thin films due to lattice constant mismatches, the properties of epitaxial thin films are also influenced by the same substrates with different crystal orientations. Herein, the (111)‐oriented SrTiO3 (STO) substrates are used to fabricate the LaCoO3 (LCO) epitaxial thin films rather than the more common (001)‐oriented STO substrates. It undergoes one paramagnetic–ferromagnetic phase transition around 50 K. This phase transition is similar to the previously observed for (001)‐LCO/STO, but the Curie temperature (Tc) is significantly lower than the previously reported 80 K. To investigate the decrease of Tc and gain further insight into the phase transition, the critical behavior analysis of thin film is performed. The critical exponents are determined to be β = 1.591(3) and γ = 0.937(1) by reconstructing a modified Arrott plot, and the reliability of these exponents is confirmed by the Widom scaling relation. Using the renormalization group theory approach, it is discovered that the film has a long‐range magnetic interaction with space dimensionality d = 2 and spin dimensionality n = 1, and the magnetic exchange interaction decays J(r)≈r−2.4473. [ABSTRACT FROM AUTHOR]

Active Lamb wave detection is an effective and simple monitoring method for structural health monitoring (SHM). Piezoelectric lead zirconate titanate (PZT) ceramics are most commonly used as transducers to excite and receive Lamb wave. However, due to their hardness, thickness and brittleness, PZT ceramics are severely limited in detecting damage on curved surface structures. Herein, we report that flexible PZT film sensor is an excellent candidate for receiving Lamb wave used in Lamb wave-based SHM of aircraft. An improved piezoelectric coefficient d 33 (~130 pm V−1) is obtained in epitaxial PZT films grown on flexible inorganic mica substrates via van der Waals heteroepitaxy. Superior stable ferroelectricity and piezoelectricity retain in flexible PZT film after bending 104 cycles under a radius of 8 mm. As proven by experiment and simulation, flexible PZT film is demonstrated as an ultrasonic sensor with high sensitivity to be bonded on the curved aluminum plate for Lamb wave-based damage monitoring. Our work demonstrates that flexible PZT films have enormous potential for real-time light-weight and high-sensitivity receiver sensors for the SHM of aging aircraft. [ABSTRACT FROM AUTHOR]

Materials that undergo a magnetostructural transition (MST) usually exhibit fascinating magnetoresponsive properties, making them an important class of smart materials. However, practical application of this class of smart materials has been hindered by structural degradation as well as large irreversibility of the MST during consecutive thermal and field cycles. Here we report a significant improvement of the reversibility and mechanical stability in grain-oriented MnNiGe-based alloys that were fabricated using a directional solidification method. The preferred grain orientation enables synergistic deformations between neighboring grains during the MST, leading to a substantial reduction in the transition-induced stress concentration. As a result, in situ and ex situ microscopic observations demonstrate a good mechanical stability of the textured alloys across the MST, in strong contrast to conventional MM'X (M, M' = Mn, Fe, Co, Ni; X = Si, Ge) materials with randomly-oriented grains. The detailed transition stages of the MST have also been observed at the microscopic scale, and are reported for the first time in the MM'X family. Besides, a low thermal hysteresis (ΔT hys) of ∼ 4 K was obtained in the textured alloys, which is the lowest ΔT hys in the MM'X material family. Textured MnNiGe-based alloys show a large reversible isothermal entropy change (≥ 35.9 Jkg−1K−1) in a 5 T field change, which is the highest among typical magnetocaloric materials. Consequently, this work provides a promising strategy for enhancing the cyclic stability of materials with a MST, which may boost their practical applications in solid-state refrigerators, energy harvesters and high-precision actuators. [Display omitted] [ABSTRACT FROM AUTHOR]

The fabrication of brittle magnetocaloric materials into heat exchangers is currently challenging for conventional manufacturing techniques. In the present study, we demonstrated that selective laser melting (SLM), an emerging 3D printing technique, offers a new and promising solution to fabricate the (Mn,Fe)2(P,Si) magnetocaloric alloys for magnetic refrigeration applications. The hexagonal (Mn,Fe)2(P,Si) phase, which shows a first-order magnetic transition, is successfully formed in the SLM-printed samples with a very small amount of impurity phase (less than 2% in volume fraction). The SLM processing parameters (e.g., the laser power and scanning speed) have a strong influence on the microstructure, magnetic phase transition and magnetocaloric properties of the printed samples. The microscopic mechanism underlying the changes in the microstructure and phase transition temperature has also been discussed. Besides that, a large isothermal entropy change, more than three times higher than that of the benchmark Gd material in a field change of 1 and 2 T, has been obtained in the SLM-printed samples. [ABSTRACT FROM AUTHOR]

• The electronic phase separation has been observed in La 0.8 Sr 0.2 MnO 3. • The state of magnetic skyrmion exists in the temperature region of 290 K–306 K. • A large DM interaction exists in the interface of LaMnO 3 /SrMnO 3. Magnetic skyrmions, being one of the most promising candidates for the next generation memory-type application due to their nanometer-size and efficient current-driven dynamics, are mainly found and studied in alloy helimagnets in which the spin-orbit coupling induced by Dzyaloshinskii-Moriya interaction (DMI) enables noncollinear spin alignment and skyrmion formation. In this paper, we report a possible finding of skyrmions crystal near room-temperature in centrosymmetric structures perovskite manganite La 0.8 Sr 0.2 MnO 3 (LSMO). Based on the measurements of isothermal magnetization around the Curie temperature (∼298 K), an unusual magnetic behavior of a discontinuous magnetization was observed and existed only at moderate magnetic field region together with a narrow temperature range from 306 to 290 K. Apart from this range, all curves return to conventional magnetic behavior of continuous change with external magnetic field. This characteristic has been frequently observed in some reported helimagnets (such as FeGe, MnSi), implying the possible existence of skyrmions crystal in LSMO. To further unveil the physical origin and underlying mechanisms, we performed the first-principles calculation for LSMO compound and a large DMI (Δ E DMI = 13.46 meV, d 1 = 1.68 meV) was found to exists at the interface of LaMnO 3 / SrMnO 3 layers. This result not only supports our experimental findings in the present composition but also is consistent with the formation mechanism of magnetic skyrmions. [ABSTRACT FROM AUTHOR]

Perovskite oxide SrVO 3 (SVO) is a transparent conductor with excellent optical and electrical properties. Most of the previous works have focused on (001)-oriented SVO thin films. As an alternative to tin-doped indium oxide (ITO), the other orientations of SVO thin films are important to be considered as well. In the present work, the optical and electrical properties of (111)-oriented SVO epitaxial films have been investigated. Excellent electrical conductivity (2.92 × 104 S cm−1) and optical transparency (56.6%) have been demonstrated, which are comparable to those of ITO and expand the applications of epitaxial SVO thin films in other orientations as transparent conducting oxide. [ABSTRACT FROM AUTHOR]

Highlights • Synthesis time of (Mn,Fe) 2 (P,Si) alloys is greatly shortened using the new method. • Samples using industrial-grade raw materials show superior magnetocaloric property. • Fe 3 Si-type impurity phase in the as-prepared sample is eliminated by post annealing. Abstract We have demonstrated a time-, energy-, and cost-efficient way of preparing (MnFe) 2 (P,Si)-type magnetocaloric materials, i.e. , via electromagnetic levitation melting and post-annealing from industrial-grade starting materials. The structural evolution and its influence on the magnetocaloric properties during post-annealing have been intensively studied. We found that some Fe 3 Si-type impurity phase with a size of around 5 μm is present in the as-prepared sample, which can be eliminated through high-temperature annealing. The sample annealed at 1373 K for 5 h shows a homogeneous element distribution and negligible amount of the impurity phase. A Δ S max value of 17 Jkg−1 K−1 for a field change of 2 T has be realized in the present work, which is comparable to the highest Δ S max values in the (MnFe) 2 (P,Si)-type samples produced via time- and energy-consuming solid-state reaction. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance (EPR) was applied extensively to probe the phase separation and spin relaxation mechanism in the perovskite manganites. In this study, we conducted the measurement of EPR for the perovskite manganites (La 0.5 Pr 0.5 ) 0.67 Ca 0.33 MnO 3 . We found that both paramagnetic and ferromagnetic resonance peaks simultaneously emerged on resonance spectrum near below T C , exhibiting a typical characteristic of phase separation. The linewidth of EPR spectrum progressively enlarged upon the rising of temperature in the temperature range of T > T C and a quasilinear variation of peak-peak width was observed at T C < T < 500 K. In contrast to the usual beliefs that the variation of peak-peak linewidth can be understood either by spin-lattice relaxation or by spin-spin relaxation, however, the linewidth behavior observed here shows a coexistence of two spin relaxation mechanisms. We proposed that the inhomogeneous electronic phases due to the intrinsic self-organizing growth were responsible for the appearance of multiple spin exchange interactions and variational relaxation mechanism. This finding would be possible to pave a new way for further investigating magnetic correlations and spin dynamics in the paramagnetic hole-doped manganites. [ABSTRACT FROM AUTHOR]

Polycrystalline La 0.825 Sr 0.175 MnO 3 was prepared by solid state reaction method. It exhibits a ferromagnetic–paramagnetic phase transition at T C ∼ 286 K. The intrinsic magnetic properties were clarified by the scaling theory and the isothermal magnetization measured around T C. Based on the modified Arrott plot, Kouvel–Fisher method and Widom relation, the critical exponents are determined to be β = 0. 308 (7) , γ = 1. 065 (8) , δ = 4. 457 (17). Normalization of the critical exponents shows that the extended exchange interaction decays with J ∼ r − 4. 861 , consistent with Tricritical mean field model. Rhodes–Wohlfarth ratio P C / M S >1 suggests that La 0.825 Sr 0.175 MnO 3 is completely itinerant ferromagnet. [Display omitted] • La 0.825 Sr 0.175 MnO 3 shows FM–PM phase transition at 286 K. • Its critical exponents (β = 0.308, γ = 1.065) were determined by the scaling theory. • Its phase transition belongs to Tricritical mean field model. [ABSTRACT FROM AUTHOR]

• Low-cost flexible transparent conductive oxide (TCO) film. • Low-cost, indium-free and flexible perovskite CaVO 3 TCO films grown on mica substrates. • Superior stable optical transparency and electrical conductivity after 105 bending cycles. Transparent conducting oxides (TCOs), such as indium-tin oxide (ITO) and indium gallium zinc oxide (IGZO), are essential components in the design of flexible optoelectronic devices. However, it is still a challenge to prepare low-cost flexible transparent conductive film for achieving the flexible functionality together with high optical transparency and electrical conductivity. Herein, fluorphlogopite (mica) is selected as the bendable and transparent substrate for the fabrication of low-cost perovskite CaVO 3 TCO epitaxial film. Benefitting from thin mica substrate with high Young's modulus of 200 GPa, flexible CaVO 3 TCO epitaxial film exhibits high mechanical stability in terms of electrical conductivity and optical transparency after bending up to 105 cycles. The change of resistance can reflect the bending curvature and strain state. Our results provide a new pathway to design superior mechanical flexibility and stability CaVO 3 TCO films for application in flexible, light-weight, and portable smart optoelectronic devices. [ABSTRACT FROM AUTHOR]

We have studied the evolution of Griffiths phase and the magnetic ordering state in the intermetallic compound LaCeCo 7. A ferromagnetic-like ordering phase is built up at 260 K but an anomalous magnetic susceptibility related to the Griffiths phase occurs in 300 K. The studies of critical behavior confirm that LaCeCo 7 exhibits a second-order paramagnetic-ferromagnetic phase transitions. The critical exponents of β = 0.665, γ = 1.151, and δ = 2.728 determined by the magnetic field dependence on magnetic entropy change method deviate a little from the theoretical estimated long-range mean-field model (β = 0.5, γ = 1.0, and δ = 3.0). This result implies that the disorder effect in the intermetallic LaCeCo 7 possibly plays a key role on the anomalous critical behavior and the establishment of magnetic ordering phase. [ABSTRACT FROM AUTHOR]

• The critical behavior of (Ce 0.65 Pr 0.35) 2 Co 7 alloy has been clarified with different methods. • The accurate Curie temperature of 214 K has been confirmed by the Arrott plot and ac magnetic susceptibility. • The magnetic coupling of (Ce 0.65 Pr 0.35) 2 Co 7 alloy belongs to long-range FM interaction. Clarification of magnetic phase transition nature and critical behavior is an essential step in the development of new magnetic functional materials. In this work, we studied critical properties of intermetallic compound (Ce 0.65 Pr 0.35) 2 Co 7 by bulk dc magnetization around the paramagnetic to ferromagnetic phase transition. It exhibits a second-order magnetic phase transition with T C = 214 K. Critical exponents β = 0.546(5) and γ = 1.054(5) are obtained by the modified Arrott plot, whereas δ = 2.843 is obtained by a critical isotherm analysis at T C. These critical exponents not only obey the Widom relation δ = 1 + γ / β , but also collapse the isothermal magnetization M-H-T data into two branches below and above T C following the single scaling equation M(H, ε) = ε β f ± (H/ ε β + γ ). Although the obtained exponents are close to the theoretical values of mean-field model, a noticeable deviation unable to be ignored, indicating the existence of localized magnetic interaction which competes with a long-range ferromagnetic state. Our results will establish a sound theoretical basis for understanding the complex magnetic interaction in the light rare earths ternary alloy. [ABSTRACT FROM AUTHOR]

The influence of Nb substitution on the structure, magnetoelastic transition and magnetocaloric properties has been investigated for the Mn 1.1 Fe 0.85- x Nb x P 0.43 Si 0.57 alloys. The substitution for Fe by merely 4.7 at.% Nb (i.e. x = 0.04) significantly diminishes the thermal hysteresis from 10 to 1 K due to the reduced structural discontinuity crossing the magnetoelastic transition. This also improves the mechanical stability. The Curie temperature of the magnetoelastic transition is lowered by approximately 11.6 K per at.% of the Nb substitution, originating from the enhanced covalent bonding that favors the paramagnetic state. The giant magnetocaloric effect is still retained in the Nb-substituted alloys. Image 1 • A small thermal hysteresis of 1 K was obtained in Nb-substituted Mn–Fe–P–Si alloys. • Giant magnetocaloric effect was retained in the Nb-substituted Mn–Fe–P–Si alloys. • Curie temperature can be effectively tuned by 11.6 K per at.% of Nb substitution. [ABSTRACT FROM AUTHOR]