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Showing papers on "Curie temperature published in 2014"


Journal ArticleDOI
TL;DR: The evaluated low cleavage energy and high in-plane stiffness indicate that the free-standing MnPSe3 nanosheet can be exfoliated from its bulk structure in experiment, and render the 2D Mn PSe3 crystal with great potentials for application in electric-field controlled spintronic devices.
Abstract: Searching two-dimensional (2D) half-metallic crystals that are feasible in experiment is essential to develop next-generation nanospintronic devices. Here, a 2D exfoliated MnPSe3 nanosheet with novel magnetism is first proposed based on first-principles calculations. In particular, the evaluated low cleavage energy and high in-plane stiffness indicate that the free-standing MnPSe3 nanosheet can be exfoliated from its bulk structure in experiment. The MnPSe3 nanosheet is an antiferromagnetic semiconductor at its ground state, whereas both electron and hole doping induce its transition from antiferromagnetic semiconductor to ferromagnetic half-metal. Moreover, the spin-polarization directions of 2D half-metallic MnPSe3 are opposite for electron and hole doping, which can be controlled by applying an external voltage gate. The Monte Carlo simulation based on the Ising model suggests the Curie temperature of the doped 2D MnPSe3 crystal is up to 206 K. These advantages render the 2D MnPSe3 crystal with great potentials for application in electric-field controlled spintronic devices.

349 citations


Journal ArticleDOI
TL;DR: In this paper, the preparation of 3D transition metal-doped EuO thin films by molecular beam epitaxy is investigated using the example of Sc doping, which leads to an enhancement of the Curie temperature to up to 125
Abstract: The preparation of 3d-transition metal-doped EuO thin films by molecular beam epitaxy is investigated using the example of Sc doping. The Sc-doped EuO samples display a good crystalline structure, despite the relatively small ionic radius of the dopant. The Sc doping leads to an enhancement of the Curie temperature to up to 125 K, remarkably similar to previous observations on lanthanide-doped EuO.

309 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed a quantum anomalous Hall platform with a large energy gap of 0.34 and 0.06 eV on honeycomb lattices comprised of Sn and Ge.
Abstract: Recently, the long-sough quantum anomalous Hall effect was realized in a magnetic topological insulator. However, the requirement of an extremely low temperature (approximately 30 mK) hinders realistic applications. Based on ab initio band structure calculations, we propose a quantum anomalous Hall platform with a large energy gap of 0.34 and 0.06 eV on honeycomb lattices comprised of Sn and Ge, respectively. The ferromagnetic (FM) order forms in one sublattice of the honeycomb structure by controlling the surface functionalization rather than dilute magnetic doping, which is expected to be visualized by spin polarized STM in experiment. Strong coupling between the inherent quantum spin Hall state and ferromagnetism results in considerable exchange splitting and, consequently, an FM insulator with a large energy gap. The estimated mean-field Curie temperature is 243 and 509 K for Sn and Ge lattices, respectively. The large energy gap and high Curie temperature indicate the feasibility of the quantum anomalous Hall effect in the near-room-temperature and even room-temperature regions.

251 citations


Journal ArticleDOI
TL;DR: The partial substitution of B for P in MnFe(P,Si,B) compounds is found to be an ideal parameter to control the latent heat observed at the Curie point without deteriorating the magnetic properties, which results in promising magnetocaloric properties suitable for magnetic refrigeration.
Abstract: Large magnetically driven temperature changes are observed in MnFe(P,Si,B) materials simultaneously with large entropy changes, limited (thermal or magnetic) hysteresis, and good mechanical stability. The partial substitution of B for P in MnFe(P,Si) compounds is found to be an ideal parameter to control the latent heat observed at the Curie point without deteriorating the magnetic properties, which results in promising magnetocaloric properties suitable for magnetic refrigeration.

234 citations


Journal ArticleDOI
TL;DR: In this article, cobalt-dysprosium ferrite nanoparticles with the chemical formula Co1−xDyxFe2O4 were synthesized by the co-precipitation chemical method and then analyzed from the structural and magnetic perspectives.

170 citations


Journal ArticleDOI
TL;DR: In this article, the effect of variation in the rare-earth substitution and its impact on particle size, magnetic properties like M S, H C and Curie temperature were investigated by using the chemical co-precipitation method.

166 citations


Journal ArticleDOI
TL;DR: A new hexagonal stacking perovskite-type complex (3-pyrrolinium)(CdCl3) exhibits above-room-temperature ferroelectricity with a Curie temperature T(c)=316 K and a spontaneous polarization P(s)=5.1 μC cm(-2).
Abstract: Hybrid organo–metal halide perovskite materials, such as CH3NH3PbI3, have been shown to be some of the most competitive candidates for absorber materials in photovoltaic (PV) applications. However, their potential has not been completely developed, because a photovoltaic effect with an anomalously large voltage can be achieved only in a ferroelectric phase, while these materials are probably ferroelectric only at temperatures below 180 K. A new hexagonal stacking perovskite-type complex (3-pyrrolinium)(CdCl3) exhibits above-room-temperature ferroelectricity with a Curie temperature Tc=316 K and a spontaneous polarization Ps=5.1 μC cm−2. The material also exhibits antiparallel 180° domains which are related to the anomalous photovoltaic effect. The open-circuit photovoltage for a 1 mm-thick bulky crystal reaches 32 V. This finding could provide a new approach to develop solar cells based on organo–metal halide perovskites in photovoltaic research.

150 citations


Journal ArticleDOI
TL;DR: In this article, flux coupling phenomena such as solute drag by vacancies and radiation-induced segregation at defect sinks are systematically investigated for six bcc iron-based dilute binary alloys, containing Cr, Cu, Mn, Ni, P and Si impurities, respectively.
Abstract: Defect-driven diffusion of impurities is the major phenomenon leading to formation of embrittling nanoscopic precipitates in irradiated reactor pressure vessel (RPV) steels. Diffusion depends strongly on the kinetic correlations that may lead to flux coupling between solute atoms and point defects. In this work, flux coupling phenomena such as solute drag by vacancies and radiation-induced segregation at defect sinks are systematically investigated for six bcc iron-based dilute binary alloys, containing Cr, Cu, Mn, Ni, P, and Si impurities, respectively. First, solute-vacancy interactions and migration energies are obtained by means of ab initio calculations; subsequently, self-consistent mean field theory is employed in order to determine the exact Onsager matrix of the alloys. This innovative multiscale approach provides a more complete treatment of the solute-defect interaction than previous multifrequency models. Solute drag is found to be a widespread phenomenon that occurs systematically in ferritic alloys and is enhanced at low temperatures (as for instance RPV operational temperature), as long as an attractive solute-vacancy interaction is present, and that the kinetic modeling of bcc alloys requires the extension of the interaction shell to the second-nearest neighbors. Drag occurs in all alloys except Fe(Cr); the transition from dragging to nondragging regime takes place for the other alloys around (Cu, Mn, Ni) or above (P, Si) the Curie temperature. As far as only the vacancy-mediated solute migration is concerned, Cr depletion at sinks is foreseen by the model, as opposed to the other impurities which are expected to enrich up to no less than 1000 K. The results of this study confirm the current interpretation of the hardening processes in ferritic-martensitic steels under irradiation.

136 citations


Journal ArticleDOI
TL;DR: The combination of epitaxial strain and defect engineering facilitates the tuning of the transition temperature of BaTiO3 to >800 °C, inducing unprecedented functionality and temperature stability in ferroelectrics.
Abstract: The combination of epitaxial strain and defect engineering facilitates the tuning of the transition temperature of BaTiO3 to >800 °C. Advances in thin-film deposition enable the utilization of both the electric and elastic dipoles of defects to extend the epitaxial strain to new levels, inducing unprecedented functionality and temperature stability in ferroelectrics.

135 citations


Journal ArticleDOI
TL;DR: In this article, the electrostrictive effect in Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (BZT-xBCT, x = 0.4, 0.5, and 0.6) ceramics was investigated to gain understanding of their high piezoelectric activity.
Abstract: In this study, the electrostrictive effect in Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (BZT-xBCT, x = 0.4, 0.5, and 0.6) ceramics was investigated to gain understanding of their high piezoelectric activity. The electrostrictive coefficient Q33 of the BZT-xBCT ceramics was observed to be around 0.04 m4/C2, twice that reported for Pb(Zr,Ti)O3-based ceramics. The Q33 was found to be quite stable with respect to temperature and composition for the BZT-xBCT ceramics. The addition of Fe3+ dopant to the ceramics greatly decreased their Curie temperature without affecting their Q33, which remained 0.04 m4/C2. Moreover, a high and hysteresis-free electric-field-induced strain was obtained for 2 at. % Fe-doped BZT-0.5BCT ceramics at room temperature, caused by their high Q33 coefficient and lower-than-room-temperature Curie temperature. The small-signal M33 coefficient of 2 at. % Fe-doped BZT-0.5BCT ceramics was found to be 1.5 × 10−16 m2/V2 (0.32 × 10−16 m2/V2 for undoped counterpart). These results indicate that 2 at. ...

115 citations


Journal ArticleDOI
TL;DR: In this article, the authors report the first time how electric fields influence the sintering of undoped BaTiO 3, a ferroelectric material, and how this process affects the microstructure and the dielectric properties.
Abstract: We report, for first time, how electric fields influence the sintering of undoped BaTiO 3 , a ferroelectric material, and how this process affects the microstructure and the dielectric properties. Flash sintering is achieved at a furnace temperature of 688 °C under a field of 500 V cm −1 , producing specimens that are 94% dense. As a consequence, the grain size is much finer than in conventional sintering, which is shown to influence the Curie temperature and dielectric permittivity. Data obtained at different strengths of the electrical field, and current limits imposed on the specimen are presented in the form of a “processing map” that separates the safe region, where sintering is uniform, from the fail region, where the current flow in the sample becomes localized. The map illustrates that ceramics can respond by different mechanisms, with the dominant mechanism changing with the strength of the electrical parameters.

Journal ArticleDOI
TL;DR: High-resolution x-ray diffraction, Raman spectroscopy and total scattering XRD coupled to atomic pair distribution function (PDF) analysis studies of the atomic-scale structure of archetypal BaZrxTi(1-x)O3 reveal the presence of Ti-rich polar clusters which are precursors of a long-range ferroelectric order observed below TC.
Abstract: High-resolution x-ray diffraction (XRD), Raman spectroscopy and total scattering XRD coupled to atomic pair distribution function (PDF) analysis studies of the atomic-scale structure of archetypal BaZrxTi1?xO3 (x = 0.10, 0.20, 0.40) ceramics are presented over a wide temperature range (100?450?K). For x = 0.1 and 0.2 the results reveal, well above the Curie temperature, the presence of Ti-rich polar clusters which are precursors of a long-range ferroelectric order observed below TC. Polar nanoregions (PNRs) and relaxor behaviour are observed over the whole temperature range for x = 0.4. Irrespective of ceramic composition, the polar clusters are due to locally correlated off-centre displacement of Zr/Ti cations compatible with local rhombohedral symmetry. Formation of Zr-rich clusters is indicated by Raman spectroscopy for all compositions. Considering the isovalent substitution of Ti with Zr in BaZrxTi1?xO3, the mechanism of formation and growth of the PNRs is not due to charge ordering and random fields, but rather to a reduction of the local strain promoted by the large difference in ion size between Zr4+ and Ti4+. As a result, non-polar or weakly polar Zr-rich clusters and polar Ti-rich clusters are randomly distributed in a paraelectric lattice and the long-range ferroelectric order is disrupted with increasing Zr concentration.

Journal ArticleDOI
TL;DR: In this article, the structure, magnetic properties, and spin polarization of CoFeMnGe equiatomic quaternary Heusler alloy were reported, and the temperature dependence of electrical resistivity has been fitted in the temperature range of 5-300 K in order to check for the half metallic behavior.
Abstract: We report the structure, magnetic property, and spin polarization of CoFeMnGe equiatomic quaternary Heusler alloy. The alloy was found to crystallize in the cubic Heusler structure (prototype LiMgPdSn) with considerable amount of DO3 disorder. Thermal analysis result indicated the Curie temperature is about 750 K without any other phase transformation up to melting temperature. The magnetization value was close to that predicted by the Slater-Pauling curve. Current spin polarization of P = 0.70 ± 0.01 was deduced using point contact andreev reflection measurements. The temperature dependence of electrical resistivity has been fitted in the temperature range of 5–300 K in order to check for the half metallic behavior. Considering the high spin polarization and Curie temperature, this material appears to be promising for spintronic applications.

Journal ArticleDOI
TL;DR: In this paper, large single crystals with sizes of up to 15mm of cobalt and nickel-substituted M-type barium hexaferrite BaFe12−xMxO19 (M = Ni, Co) were obtained from carbonate flux at temperatures as low as 1260°C.

Journal ArticleDOI
TL;DR: In this article, the structure, magnetic properties and spin polarization of CoFeMnGe equiatomic quaternary Heusler alloy were reported, which was found to exist in the L21 structure with considerable amount of DO3 disorder.
Abstract: We report the structure, magnetic property and spin polarization of CoFeMnGe equiatomic quaternary Heusler alloy The alloy was found to exist in the L21 structure with considerable amount of DO3 disorder Thermal analysis result indicated the Curie temperature is about 711K without any other phase transformation up to melting temperature The magnetization value was close to that predicted by the Slater-Pauling curve Current spin polarization of P = 070 {plus/minus}01 was deduced using point contact Andreev reflection (PCAR) measurements Half-metallic trend in the resistivity has also been observed in the temperature range of 5 K to 300 K Considering the high spin polarization and Curie temperature, this material appears to be promising for spintronic applications

Journal ArticleDOI
TL;DR: In this article, the van der Waals epitaxy of the topological insulator compound Bi2Te3 on the ferromagnetic insulator Cr2Ge2Te6 was demonstrated.
Abstract: We demonstrate the van der Waals epitaxy of the topological insulator compound Bi2Te3 on the ferromagnetic insulator Cr2Ge2Te6. The layers are oriented with (001)Bi2Te3||(001)Cr2Ge2Te6 and (110)Bi2Te3||(100)Cr2Ge2Te6. Cross-sectional transmission electron microscopy indicates the formation of a sharp interface. At low temperatures, bilayers consisting of Bi2Te3 on Cr2Ge2Te6 exhibit a large anomalous Hall effect (AHE). Tilted field studies of the AHE indicate that the easy axis lies along the c-axis of the heterostructure, consistent with magnetization measurements in bulk Cr2Ge2Te6. The 61 K Curie temperature of Cr2Ge2Te6 and the use of near-stoichiometric materials may lead to the development of spintronic devices based on the AHE.

Journal ArticleDOI
14 Oct 2014-Sensors
TL;DR: It is revealed that highly crystalline P(VDF-TrFE) thin films could be induced at 100 °C by annealing the thin film with a simple and cheap method.
Abstract: Ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer 70/30 thin films are prepared by spin coating. The crystalline structure of these films is investigated by varying the annealing temperature from the ferroelectric phase to the paraelectric phase. A hot plate was used to produce a direct and an efficient annealing effect on the thin film. The dielectric, ferroelectric and pyroelectric properties of the P(VDF-TrFE) thin films are measured as a function of different annealing temperatures (80 to 140 °C). It was found that an annealing temperature of 100 °C (slightly above the Curie temperature, Tc) has induced a highly crystalline β phase with a rod-like crystal structure, as examined by X-ray. Such a crystal structure yields a high remanent polarization, Pr = 94 mC/m2, and pyroelectric constant, p = 24 μC/m2K. A higher annealing temperature exhibits an elongated needle-like crystal domain, resulting in a decrease in the crystalline structure and the functional electrical properties. This study revealed that highly crystalline P(VDF-TrFE) thin films could be induced at 100 °C by annealing the thin film with a simple and cheap method.

Journal ArticleDOI
TL;DR: In this paper, the performance of three generations of MnFe(P,X) (X = As, Ge, Si) materials has been investigated by combining indirect ΔS and direct ΔTad measurements.
Abstract: An investigation of the magnetocaloric effect (MCE) displayed by three generations of MnFe(P,X) (X = As, Ge, Si) materials has been carried out by combining indirect ΔS and direct ΔTad measurements. To be able to compare the performances of the new Si-based system with the already well-known As- and Ge-based materials in optimal conditions, both the Mn/Fe and P/Si ratios of the MnxFe1.95−xP1−ySiy compounds were optimized to display the largest MCE around room temperature. Here, we show that the maximum values of ΔTad (ΔB = 1.1 T) and ΔS (ΔB = 1 T) are respectively ∼2.2 K and ∼8 J kg−1 K−1 in the Si-based material Mn1.25Fe0.7P0.49Si0.51. These values are very close to the MCE performances of the As-based and Ge-based compounds. A critical comparison of these three MnFe(P,X) series highlights the role played by the non-magnetic elements on the latent heat at the Curie temperature. The combination of: (i) large ΔS and ΔTad in intermediate magnetic fields, (ii) limited thermal/magnetic hysteresis, (iii) easy tunability of the Curie temperatures and (iv) practical advantages like cheap, non-critical and non-toxic starting materials; makes the MnxFe1.95−xP1−ySiy family highly promising for magnetic refrigeration applications.

Journal ArticleDOI
TL;DR: In this paper, the van der Waals epitaxy of the topological insulator compound Bi2Te3 on the ferromagnetic insulator Cr2Ge2Te6 was demonstrated.
Abstract: We demonstrate the van der Waals epitaxy of the topological insulator compound Bi2Te3 on the ferromagnetic insulator Cr2Ge2Te6. The layers are oriented with (001) of Bi2Te3 parallel to (001) of Cr2Ge2Te6 and (110) of Bi2Te3 parallel to (100) of Cr2Ge2Te6. Cross-sectional transmission electron microscopy indicates the formation of a sharp interface. At low temperatures, bilayers consisting of Bi2Te3 on Cr2Ge2Te6 exhibit a large anomalous Hall effect (AHE). Tilted field studies of the AHE indicate that the easy axis lies along the c-axis of the heterostructure, consistent with magnetization measurements in bulk Cr2Ge2Te6. The 61 K Curie temperature of Cr2Ge2Te6 and the use of near-stoichiometric materials may lead to the development of spintronic devices based on the AHE.

Journal ArticleDOI
TL;DR: In this article, a modified spectral analysis technique, the de-fractal spectral depth method, is developed and used to estimate the top and bottom boundaries of the magnetised layer.

Journal ArticleDOI
TL;DR: An ab initio based framework for quantitatively assessing the phonon contribution due to magnon-phonon interactions and lattice expansion is developed, demonstrating the strong impact of magnetic short-range order even significantly above the Curie temperature.
Abstract: An ab initio based framework for quantitatively assessing the phonon contribution due to magnon-phonon interactions and lattice expansion is developed. The theoretical results for bcc Fe are in very good agreement with high-quality phonon frequency measurements. For some phonon branches, the magnon-phonon interaction is an order of magnitude larger than the phonon shift due to lattice expansion, demonstrating the strong impact of magnetic short-range order even significantly above the Curie temperature. The framework closes the previous simulation gap between the ferro- and paramagnetic limits.

Journal ArticleDOI
TL;DR: The quasi two-dimensional structure endows the doped La(Mn,Zn)AsO alloy a sizable magnetic anisotropy energy with the magnitude of at least one order larger than those of Fe, Co, and Ni bulks.
Abstract: Exploring half-metallic materials with high Curie temperature, wide half-metallic gap, and large magnetic anisotropy energy is one of the effective solutions to develop high-performance spintronic devices. Using first-principles calculations, we design a practicable half-metal based on a layered La(Mn0.5Zn0.5)AsO alloy via element substitutions. At its ground state, the pristine La(Mn0.5Zn0.5)AsO alloy is an antiferromagnetic semiconductor. Either hole doping via (Ca(2+)/Sr(2+),La(3+)) substitutions or electron doping via (H(-)/F(-),O(2-)) substitutions in the [LaO](+) layer induce half-metallicity in the La(Mn0.5Zn0.5)AsO alloy. The half-metallic gap is as large as 0.74 eV. Monte Carlo simulations based on the Ising model predict a Curie temperature of 475 K for 25% Ca doping and 600 K for 50% H doping, respectively. Moreover, the quasi two-dimensional structure endows the doped La(Mn,Zn)AsO alloy a sizable magnetic anisotropy energy with the magnitude of at least one order larger than those of Fe, Co, and Ni bulks.

Journal ArticleDOI
TL;DR: In this paper, the structural, magnetic and magnetocaloric properties of Zn-doped nickel-zinc ferrites with different Zn concentrations were investigated using X-ray diffraction results.

Journal ArticleDOI
TL;DR: In this paper, a modified 0.75BF-0.25BT with 1% excess Bi contents was used for high-temperature and lead-free piezoelectric applications.

Journal ArticleDOI
TL;DR: In this article, the authors constructed an integrated magnetic anomaly map of Taiwan and its vicinity that combines land magnetic data and marine magnetic data using the reduction to pole (RTP) correction method.

Journal ArticleDOI
TL;DR: In this article, the structural and magnetic properties of the nanoparticles were investigated in detail, and the results suggest that those nanoparticles could be useful for magnetic refrigeration in a broad temperature range.

Journal ArticleDOI
TL;DR: In this paper, the intrinsic exchange interaction of Co ions and VZn, Oi related defects was quantitatively analyzed and explained using a bound magnetic polaron model and provided a better insight into the underlying mechanisms of high temperature ferromagnetism in Zn1−xCoxO NRs.

Journal ArticleDOI
TL;DR: In this article, phase-pure multiferroic bismuth ferrite (BFO) nanoparticles were synthesized by energy efficient, simple and low temperature sol-gel followed by auto-combustion route.

Journal ArticleDOI
TL;DR: The effects of partial substitution of manganese by iron on the physical properties of Pr0.6Ca0.1Sr0.3Mn1−xFexO3 (0.

Journal ArticleDOI
TL;DR: In this article, single phase nanostructured Eu-Ni substituted Y-type hexaferrites with nominal composition Sr 2 Co 2− x Ni x Eu y Fe 12− y O 22 ( x ǫ = 0.0 − 1, y Ǫ = 0 − 0.1) were synthesized by the normal microemulsion method and X-ray diffraction (XRD) technique was employed for phase analysis and indexing of each pattern corroborates that well defined Y type crystalline phase is formed.