Reduced Transition Temperature Research Articles

Enhanced visible transmittance and reduced transition temperature for VO2 thin films modulated by index-tunable SiO2 anti-reflection coatings.

The low visible transmission is one of the bottleneck problems for the application of vanadium dioxide films since the high refractive index (RI) of VO2 films results in strong reflection in the visible wavelength. To address this problem, in this paper, high-purity VO2 films were deposited on fused silica by DC reactive magnetron sputtering at low temperature of 320 °C. Silica sol–gel coatings with tunable refractive index (RI) coated onto VO2 films have been fabricated to enhance visible transmittance with the potential application in the field of smart windows. SiO2 coatings with tunable RI (1.16–1.42 at λ = 700 nm) were prepared by sol–gel dip-coating technique. The double structure SiO2/VO2 films were characterized through several techniques, including X-ray diffraction, UV-VIS-NIR spectrophotometry and scanning electron microscopy. Compared with the single-layer VO2 film (ΔTsol of 6.25% and Tlum of 38.58%), the three kinds of SiO2/VO2 bilayer films had higher Tlum (41.93–50.44%) and larger ΔTsol (8.15–8.51%) simultaneously due to significantly decreased reflectance. Moreover, the crystallization properties of VO2 films are essentially unchanged by applying a SiO2 top layer, while the phase transition temperature and thermal hysteresis width of sample S116 are lower than those of pure VO2 film. The presented RI-tunable SiO2 coatings, can regulate optical properties continuously for various VO2 substrates, paving the way for practical applications of VO2 films in the field of smart windows or others.

Synthesis of colloidal VO2 nanoparticles for thermochromic applications

Vanadium dioxide (VO2) thin films are key materials for thermochromic smart windows and commonly have a typical phase transition (insulator to metal phase) at a transition temperature of 68°C. This research, however, found that highly crystallized VO2 nanoparticles can be successfully coated on a glass substrate with added functionalities, such as higher luminous transmittance and transition efficiency. The transition temperature revealed that the VO2 nanoparticles with post thermal treatment at 600°C also clearly exhibited a reduced transition temperature of 69°C in the heating curve, 59°C in the cooling curve, and a transition width of 10°C. By nanopatterning the thin films, we were able to prepare VO2 thin films with higher luminous transmittance than that attained with non-patterned VO2 thin films. The enhanced transition property was demonstrated using highly crystallized VO2 nanoparticles induced by post thermal treatment, and the luminous transmittance was improved by the nanopatterns on the surface of the VO2 thin films.

Magnetic properties in stacked triangular lattice: Monte Carlo approach

We study the magnetic properties of mixed spins σ=5∕2 and S=2 Ising in stacked triangular lattice (STL) using Monte Carlo approach. We have also give the grounds state phase diagrams of mixed spins-5/2 and 2. The different magnetic phases are detected under effect of different physical parameters. The diagrams show some key features: coexistence between regions, points where three, four and five states can coexist. The reduced critical temperatures have been also determined for different exchange interactions in each layer with a fixed value of exchange interactions between two layers. The total magnetization with reduced exchange interactions and crystal-fields of mixed spins is obtained. The multiple hysteresis and the superparamagnetic behavior are established around the reduced critical temperatures. The magnetic coercive field and magnetization remanent increase with increasing the exchange interactions and decreases with increasing the temperature values. The obtained results are similar to those obtained by experiment and theoretically results. Above reduced transition temperature the system shows superparamagnetic behavior which makes the material desirable for biomedical applications.

Magnetic properties of checkerboard lattice: a Monte Carlo study

The magnetic properties of ferrimagnetic mixed-spin Ising model in the checkerboard lattice are studied using Monte Carlo simulations. The variation of total magnetization and magnetic susceptibility with the crystal field has been established. We have obtained a transition from an order to a disordered phase in some critical value of the physical variables. The reduced transition temperature is obtained for different exchange interactions. The magnetic hysteresis cycles have been established. The multiples hysteresis cycle in checkerboard lattice are obtained. The multiples hysteresis cycle have been established. The ferrimagnetic mixed-spin Ising model in checkerboard lattice is very interesting from the experimental point of view. The mixed spins system have many technological applications such as in domain opto-electronics, memory, nanomedicine and nano-biological systems. The obtained results show that that crystal field induce long-range spin–spin correlations even bellow the reduced transition temperature.

Improvement in dielectric, piezoelectric and ferroelectric properties of 0.64PMN–0.36PT ceramics by Sb modification

Pure and Sb-doped 0.64PMN–0.36PT (PMN–PT) ceramics near MPB have been prepared using columbite precursor technique. The effects of Sb-doping on microstructure and electrical properties were studied systematically. Powder XRD and SEM exhibited the formation of pure perovskite phase with homogeneous microstructure. As compared to the pure PMN–PT ceramics, enhanced dielectric constant, and reduced transition temperature (Tm) and dielectric loss (tan δ) were observed for Sb-doped PMN–PT ceramics. Displacement–Voltage (D–V) butterfly hysteresis loops and quasi-static d33 meter revealed a higher value of piezoelectric charge coefficient (d33) for Sb-doped sample (644 pm/V and 551 pC/N) as compared to pure ceramic (435 pm/V and 410 pC/N). P–E hysteresis curves showed improved ferroelectric properties after Sb doping. A high value of pyroelectric coefficient (p ∼ −1170.4 µC m−2 °C−1) for Sb-doped PMN–PT ceramic was obtained. Sb-doped PMN–PT ceramic showed an excellent anti-fatigue nature over 107 switching cycles. Small leakage current was evident from J–E analysis for both the ceramics. Therefore, Sb-doped PMN–PT ceramic proved to be a better choice for applications in the electronic ceramic industries.

Magnetic properties of multilayered with alternating magnetic wires with the mixed spins-2 and 5/2 ferrimagnetic Ising model

The magnetic properties of multilayered with alternating magnetic wires with the mixed spins-2 and 5/2 ferrimagnetic Ising model have been studied using the Monte Carlo simulations. We have given the ground state phase diagrams of a mixed Ising model on a multilayered with alternating magnetic wires with the mixed spins S (±2, ±1,0) and σ(±5/2, ±3/2,±1/2). The proposed Hamiltonian includes exchange interactions, crystal field and external magnetic field. The reduced transition temperature is deduced for a fixed value of layers. The effect of the exchange interactions and the crystal field on the magnetization of several layers has been investigated for a fixed values of layer with spin-3/2 and varying the layer values with spin-2. Magnetic hysteresis cycles of multilayered with alternating magnetic wires with the mixed spins-2 and 5/2 ferrimagnetic Ising model for several of exchange interactions between the mixed spins (S and σ), sizes of layers and temperatures values have been established.

Magnetic properties of zigzag metallic chains: A Monte Carlo study

The magnetic properties of zigzag metallic chains have been calculated based on the Monte Carlo simulation. The reduced transition temperatures and the magnetization have been obtained for different exchange interactions and for different crystal fields. The hysteresis cycle is obtained for different exchange interactions, temperatures and crystal field. The superparamagnetic behavior is obtained for a specific value of temperatures and crystal field. The second-order phase transitions are also observed. The obtained results are comparable with some given by experiment results and theoretical calculations.

Monte Carlo Study of Magnetic and Thermodynamic Properties of a Ferrimagnetic Ising on the Bathroom Tile (4–8) Lattice

The magnetic properties of mixed spins-1 and 3 /2 Ising model on a bathroom tile (4–8) lattice are studied by Monte Carlo simulation. The total magnetization and the magnetization of each sub-lattice of the mixed-spin lattice have been studied. The reduced transition temperatures are deduced. The variation of the total magnetization with the exchange interactions and the crystal fields is given. Magnetic hysteresis cycle is deduced. Magnetization plateaus appear on the magnetization curves at low temperature.

Magnetic properties of a single iron atomic chain encapsulated in armchair carbon nanotubes: A Monte Carlo study

The magnetic properties have been investigated of FeCuxC1−x for a Fe atom chain wrapped in armchair (N,N) carbon nanotubes (N=4,6,8,10,12) diluted by Cu2+ ions using Monte Carlo simulations. The thermal total magnetization and magnetic susceptibility are found. The reduced transition temperatures of iron and carbon have been calculated for different N and the exchange interactions. The total magnetization is obtained for different exchange interactions and crystal field. The Magnetic hysteresis cycles are obtained for different N, the reduced temperatures and exchange interactions. The multiple magnetic hysteresis is found. This system shows it can be used as magnetic nanostructure possessing potential current and future applications in permanent magnetism, magnetic recording and spintronics.

Magnetism in Nanoislands: a Monte Carlo Study

The properties of nanoislands consisting of mixed spins-2 and -5/2 have been investigated using Monte Carlo simulations. Some interesting phenomena have been found in the thermal variations of the nanoisland system. The shapes of total magnetization and total magnetic susceptibility are greatly influenced by the exchange couplings. The reduced transition temperature of the nanoisland is deduced. The magnetic hysteresis cycles are obtained for different temperatures, crystal fields, and exchange interactions. Some results obtained in the nanoisland may have potential applications in different research fields, such as electronics, optics, mechanics, and even biomedicine and molecular devices.

Magnetic properties of bilayer graphene armchair nanoribbons: A Monte Carlo study

In this work, the lattice structure of bilayer graphene armchair nanoribbons atoms within the same layer are studied by Monte Carlo simulations. The ground state phase diagrams of mixed spin-3 and spin-7/2 Ising model on a of bilayer graphene armchair nanoribbons are studied using the Monte Carlo simulations. The reduced transition temperatures with the exchange interactions have been given. The total magnetization and magnetic susceptibility with the crystal field have been established for different plane exchange interactions. Finally, we have given the magnetic hysteresis cycle for different plane exchange interactions, different temperatures, and different crystal field in bilayer graphene armchair nanoribbons. The bilayer graphene armchair nanoribbons exhibit the superparamagnetic behavior at the reduced transition temperature and for a fixed of crystal field.

Magnetic properties of bilayer graphene: a Monte Carlo study

The lattice structure of bilayer graphene atoms within the same layer is studied by Monte Carlo simulations. The ground-state phase diagrams of mixed spin-2 and spin-3/2 with Ising model on a bilayer graphene are investigated using the Monte Carlo simulations. The reduced transition temperatures for the plane and interplane exchange interactions and for different crystal fields have been obtained. The total magnetization and magnetic susceptibility with the crystal field have been established for different plane exchange interactions. We have also given the magnetic hysteresis cycle for different plane exchange interactions, different temperatures, and with different crystal fields in bilayer graphene. Finally, the system exhibits the superparamagnetic phase at the reduced transition temperature and for a fixed crystal field.

Magnetocaloric effect in NdSi compound: a Monte Carlo simulation

Magnetic properties and magnetocaloric effects of the compound NdSi are studied by means of Monte Carlo simulations. NdSi can be considered as a competitive candidate of magnetic refrigeration. The thermal magnetization, dM/dT, magnetic entropy, and the specific heat of NdSi are given for different values of magnetic field and exchange interactions with a fixed crystal field. The magnetic entropy changes and those of the adiabatic temperature for different values of magnetic field and exchange interactions with a fixed crystal field are given. The reduced transition temperature of compound NdSi is obtained. The relative cooling power of NdSi has been obtained for different values of exchanges interactions and magnetic field. The magnetic hysteresis cycles of NdSi are obtained for different values of exchanges interactions and different values of reduced temperatures. With the merits of the large [InlineEquation not available: see fulltext.] and without hysteresis loss, NdSi can be considered as a competitive candidate of magnetic refrigeration in the low-temperature range.

Low-temperature deposition of thermochromic VO2 thin films on glass substrates

Highly dense and highly crystalline vanadium dioxide (VO2) thermochromic thin films were successfully sputter-deposited on glass substrates at a low substrate temperature of 300°C. By superimposition of RF and DC magnetron sputtering, we were able to fabricate VO2 films with high solar transition efficiency (△Tsol) of 12.8% at a substrate temperature of 300°C, which was comparable to the results attained at 450°C by conventional DC sputtering. The VO2 crystallization at a lower temperature of 300°C could be achieved using a high-energy and high-density plasma induced by RF-superimposed DC sputtering. The hysteresis curves of transmittance as a function of temperature revealed that the VO2 films by RF-superimposed DC sputtered at 300°C exhibited a reduced transition temperature of 59°C and a narrow hysteresis width of 3°C. The enhanced transition properties might result from the compressive stress in the b and c axes as well as the densification of the films due to ion bombardment effect.

Spin compensation temperature in the Monte Carlo study of a mixed spin-1 and spin-3/2 Ising ferrimagnetic system on the decorated triangular lattice

Mixed-spin-1 and spin-3/2 Ising model on the decorated triangular lattice is studied by the use of Monte Carlo simulation. Within this approach, the results for the ground-state of the antiferromagnetic and ferromagnetic of decorated triangular lattice are obtained. The reduced transition temperature of each sublattice are obtained. The reduced temperature of compensation is also obtained. The thermal total ratio of magnetic susceptibilities of sublattices is given. The effect of crystal field and exchange interactions on the magnetization of the system are detailed. The magnetic hysteresis cycles are found for different values of exchanges interactions between the same lattice and the two sublattices different, for different crystal filed and temperatures. In addition, very weak exchange interactions and for a higher temperatures and a higher crystal filed values the decorated triangular lattice has been exhibited the superparamagnetic behavior.

Nodal versus nodeless superconductivity in isoelectronic LiFeP and LiFeAs

Nodal superconductivity is observed in LiFeP while its counterpart LiFeAs with similar topology and orbital content of the Fermi surfaces is a nodeless superconductor. We explain this difference by solving, in the two-Fe Brillouin zone, the frequency-dependent Eliashberg equations with the spin-fluctuation-mediated pairing interaction. Because of Fermi surface topology details, in LiFeAs all the $\mathrm{Fe}\text{\ensuremath{-}}{t}_{2g}$ orbitals favor a common pairing symmetry. By contrast, in LiFeP the ${d}_{xy}$ orbital favors a pairing symmetry different from ${d}_{xz/yz}$ and their competition determines the pairing symmetry and the strength of the superconducting instability: ${d}_{xy}$ orbital strongly overcomes the others and imposes the symmetry of the superconducting order parameter. The leading pairing channel is a ${d}_{xy}$-type state with nodes on both hole and electron Fermi surfaces. As a consequence, the ${d}_{xz/yz}$ electrons weakly pair, leading to a reduced transition temperature in LiFeP.

Self-Assembled Multilayer Structure and Enhanced Thermochromic Performance of Spinodally Decomposed TiO2–VO2 Thin Film

Composite films of VO2-TiO2 were deposited on sapphire (11-20) substrate by cosputtering method. Self-assembled well-ordered multilayer structure with alternating Ti- and V-rich epitaxial thin layer was obtained by thermal annealing via a spinodal decomposition mechanism. The structured thermochromic films demonstrate superior optical modulation upon phase transition, with significantly reduced transition temperature. The results provide a facile and novel approach to fabricate smart structures with excellent performance.

Giant Controllable Magnetization Changes Induced by Structural Phase Transitions in a Metamagnetic Artificial Multiferroic.

The realization of a controllable metamagnetic transition from AFM to FM ordering would open the door to a plethora of new spintronics based devices that, rather than reorienting spins in a ferromagnet, harness direct control of a materials intrinsic magnetic ordering. In this study FeRh films with drastically reduced transition temperatures and a large magneto-thermal hysteresis were produced for magnetocaloric and spintronics applications. Remarkably, giant controllable magnetization changes (measured to be as high has ~25%) are realized by manipulating the strain transfer from the external lattice when subjected to two structural phase transitions of BaTiO3 (001) single crystal substrate. These magnetization changes are the largest seen to date to be controllably induced in the FeRh system. Using polarized neutron reflectometry we reveal how just a slight in plane surface strain change at ~290C results in a massive magnetic transformation in the bottom half of the film clearly demonstrating a strong lattice-spin coupling in FeRh. By means of these substrate induced strain changes we show a way to reproducibly explore the effects of temperature and strain on the relative stabilities of the FM and AFM phases in multi-domain metamagnetic systems. This study also demonstrates for the first time the depth dependent nature of a controllable magnetic order using strain in an artificial multiferroic heterostructure.

Understanding the twist-bend nematic phase: the characterisation of 1-(4-cyanobiphenyl-4'-yloxy)-6-(4-cyanobiphenyl-4'-yl)hexane (CB6OCB) and comparison with CB7CB.

The synthesis and characterisation of the nonsymmetric liquid crystal dimer, 1-(4-cyanobiphenyl-4'-yloxy)-6-(4-cyanobiphenyl-4'-yl)hexane (CB6OCB) is reported. An enantiotropic nematic (N)-twist-bend nematic (NTB) phase transition is observed at 109 °C and a nematic-isotropic phase transition at 153 °C. The NTB phase assignment has been confirmed using polarised light microscopy, freeze fracture transmission electron microscopy (FFTEM), (2)H-NMR spectroscopy, and X-ray diffraction. The effective molecular length in both the NTB and N phases indicates a locally intercalated arrangement of the molecules, and the helicoidal pitch length in the NTB phase is estimated to be 8.9 nm. The surface anchoring properties of CB6OCB on a number of aligning layers is reported. A Landau model is applied to describe high-resolution heat capacity measurements in the vicinity of the NTB-N phase transition. Both the theory and heat capacity measurements agree with a very weak first-order phase transition. A complementary extended molecular field theory was found to be in suggestive accord with the (2)H-NMR studies of CB6OCB-d2, and those already known for CB7CB-d4. These include the reduced transition temperature, TNTBN/TNI, the order parameter of the mesogenic arms in the N phase close to the NTB-N transition, and the order parameter with respect to the helix axis which is related to the conical angle for the NTB phase.

Monte Carlo study of magnetic properties and critical behavior of Sr2CrMoO6

We performed the Monte Carlo simulation (MCs) in order to study the magnetic properties and the critical behavior of Sr2CrMoO6. Within this magnetic oxide, the Cr3+ and Mo5+ ions form two interpenetrating ferromagnetic sublattices with opposite spins directions (Cr3 +up and Mo5+down). The exchange interaction between these sublattices is assumed to be ferrimagnetic. The effects of the system parameters on critical temperatures and as a result on the phase diagrams are shown by using reduced values of parameters. The phase transitions and the magnetic stability are investigated in the framework of Ising model. For specific values of the system parameters, the existence of a compensation point is shown. Furthermore, to investigate the critical behavior, the critical exponents are calculated, they indicate that the compound belongs to a three dimensional Ising universality class. The reduced transition temperature is also found.