Crystalline Field Effects Research Articles

Dielectric Properties of a Phenanthrene-Like Nanoisland B14A10: Monte Carlo Study

The dielectric properties of a monolayer phenanthrene-like nanoisland of formula B[Formula: see text]A[Formula: see text] are examined in this research using Monte Carlo simulations. We evaluate the behaviors of the electric hysteresis loops and blocking temperature under the exchange coupling, crystalline field and temperature effects. The multi-loop hysteresis behavior examined in this research may have beneficial applications in nanotechnology and multi-state memory storage. Besides, the results found in the Phenanthrene-like nanoisland are in good agreement with several theoretical and experimental results.

Novel far-red emitting phosphor Mn4+-activated BaLaLiWO6 with excellent performance for indoor plant cultivation of light-emitting diodes

The far-red oxide phosphors doped with Mn4+ ions are constantly investigated for plant cultivation of light-emitting diodes (LEDs) due to their emission bands matching well the absorption region of phytochromes in plants. Herein, a novel far-red emitting phosphor of BaLaLiWO6 (BLLW) doped with Mn4+ ions was successfully prepared for plant cultivation. The Rietveld-refined lattice parameters and surface micromorphology of the samples were investigated. The theoretical values of the energy gap for the perfect BLLW matrix were calculated by density functional theory and the experimental values obtained based on the absorption spectra were compared. In addition, the samples can be efficiently excited by ultraviolet and blue light, and emit intense far-red light with a central wavelength of 708 nm. Furthermore, the crystalline field effect and concentration quenching mechanism of Mn4+ ions in the BLLW matrix were explored. Satisfactorily, the internal quantum efficiency, color purity, and activation energy of the phosphor were as high as 48.38%, 99.6%, and 0.53 eV, respectively. Meanwhile, the effects of synthesis temperature and Ca2+ ions co-doping on the luminescence intensity of the samples were studied. Finally, the far-red LEDs devices were prepared for plant cultivation by combining the phosphor with 460 nm LEDs chips.

Crystalline field effects on magnetic and thermodynamic properties of a ferrimagnetic-centered rectangular structure

The magnetic properties and phase diagrams of the mixed spin Ising model, with spins S=1 and {\sigma}=1/2 on a centered rectangular structure, have been investigated using Monte Carlo simulations based on the Metropolis algorithm. Every spin at one lattice site has four nearest-neighbor spins of the same type and four of the other type. We have assumed ferromagnetic interaction between the same spins type, antiferromagnetic for different spin types. An additional single-site crystal field term on the S=1 site was considered. We have shown that the crystal field enhances the existence of the compensation behavior of the system. In addition, the effects of the crystal field and exchange coupling on the magnetic properties and phase diagrams of the system have been studied. Finally, the magnetic hysteresis cycles of the system for several values of the crystal field have been found.

Magnetocaloric effect in the Nd2TIn8 (T=Rh, Ir) intermetallics

The magnetocaloric effect of Nd2TIn8 (T = Rh, Ir) intermetallics was studied theoretically. Both compounds have an antiferromagnetic interaction at low temperatures and crystallize in the same tetragonal Ho2CoGa8 structure. We considered a Hamiltonian spin model for two coupled magnetic sublattices that takes into account the effects of crystalline electrical field and exchange interaction in the mean-field approximation. The estimated crystal field parameters explain the magnetocrystalline anisotropy in these compounds and a comparison of the theoretical value of the magnetocaloric effect with the experimental one in Nd2RhIn8, and Nd2IrIn8 shows good agreement.

Characteristics of hydrogen-terminated single crystalline diamond field effect transistors with different surface orientations

Diamond has great potential applications in high-power, high-frequency semiconductor devices because of its wide band gap (5.5 eV), high thermal conductivity (22W/(cm·K)), and high carrier mobility (4500 cm<sup>2</sup>/(V·s) for electron, and 3800 cm<sup>2</sup>/(V·s) for hole). It has been widely considered as an ultimate semiconductor. From the analysis of our previous work, we find that the output current of field effect transistor based on hydrogen-terminated polycrystalline diamond is usually larger than that based on single crystal diamond, and that the preferential orientations of the polycrystalline diamond are mainly <inline-formula><tex-math id="Z-20200108113531-1">\begin{document}$ \langle 110\rangle $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20191013_Z-20200108113531-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20191013_Z-20200108113531-1.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="Z-20200108113531-2">\begin{document}$ \langle 111\rangle $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20191013_Z-20200108113531-2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20191013_Z-20200108113531-2.png"/></alternatives></inline-formula> shown by XRD results. Therefore, in order to further analyze the effect of surface orientation on the device performance of hydrogen-terminated diamond field effect transistor (FET), we study the devices fabricated respectively on the (110) plane and (111) plane single crystal diamond plates obtained from a single 3.5-mm-thick single crystal diamond grown by the microwave plasma chemical vapor deposition on the high-pressure high-temperature synthesized diamond substrate. Prior to processing the device, these diamond plates are characterized by atomic force microscope, Raman spectra and photoluminescence (PL) spectra. The results of Raman and PL spectra show that (110) plane and (111) plane plates originating from the same CVD single crystal diamond have no significant difference in optical property. Then the normally-on hydrogen-terminated diamond FET with a gate length of 6 μm is achieved. The device on (111) plane delivers a saturation drain current of 80.41 mA/mm at a gate voltage <i>V</i><sub>GS</sub> = –4 V, which is approximately 1.4 times that of the device on (110) plane. Meanwhile, the on-resistance of the device on (111) plane is 48.51 Ω·mm, and it is only 67% of the device on (110) plane. Analyses of the capacitance-voltage show that the hole concentration of the gated device on (110) plane and (111) plane are 1.34 × 10<sup>13</sup> cm<sup>–2</sup> and 1.45 × 10<sup>13</sup> cm<sup>–2</sup>, respectively, approximately at the same level. In addition, the hole density of the device on both (110) and (111) plane increase near-linearly with the increase of gate voltage from the threshold voltage to – 4 V, indicating that the control effect of the gate on the carrier in the channel is uniform. The possible reason for the higher saturation drain current as well as the lower on-resistance of the device on (111) plane is that its sheet resistance is lower.

On the issue of water activation for Portland cement

The articles is devoted to the problem of Portland cement activity increase by changing its mixing water structure due to mechanical, magnetic, electromagnetic and certain other treatments. Known facts are analyzed on specific condition and behavior of cement grout liquid phase which is determined by the effect of crystalline field of the surface of cement minerals. The authors substantiated that this condition is more important for cement behavior under hardening than the consequences of eventual structural changes in its pretreated mixing water. An original method for controlling the hardening of cement paste based on measuring the hardness of cement samples is proposed. The method allows you to control the behavior of the material itself without taking into account the influence of the size and shape of the analyzed samples.

Magnetotransport Anomaly in Room-Temperature Ferrimagnetic NiCo2 O4 Thin Films.

The inverse spinel ferrimagnetic NiCo2 O4 presents a unique model system for studying the competing effects of crystalline fields, magnetic exchange, and various types of chemical and lattice disorder on the electronic and magnetic states. Here, magnetotransport anomalies in high-quality epitaxial NiCo2 O4 thin films resulting from the complex energy landscape are reported. A strong out-of-plane magnetic anisotropy, linear magnetoresistance, and robust anomalous Hall effect above 300 K are observed in 5-30 unit cell NiCo2 O4 films. The anomalous Hall resistance exhibits a nonmonotonic temperature dependence that peaks around room temperature, and reverses its sign at low temperature in films thinner than 20 unit cells. The scaling relation between the anomalous Hall conductivity and longitudinal conductivity reveals the intricate interplay between the spin-dependent impurity scattering, band intrinsic Berry phase effect, and electron correlation. This study provides important insights into the functional design of NiCo2 O4 for developing spinel-based spintronic applications.

Antiferromagnetic exchange weakening in the TbRhIn5 intermetallic system with Y-substitution

We report measurements of the temperature dependent specific heat and magnetic susceptibility in single crystals of the series of intermetallic compounds Tb1−xYxRhIn5 (nominal concentrations x = 0.0, 0.15, 0.3, 0.4, 0.5, 0.7). A mean field approximation to simulate the macroscopic properties along the series has been used. Neutron diffraction data in powdered samples of Tb0.6Y0.4RhIn5 and Tb0.6La0.4RhIn5 reveal antiferromagnetic (AFM) propagation vector k→=[12012] with the magnetic moments oriented along the tetragonal c axis or canted from this axis, respectively for Y and La-substitutions. Considering both the simulations of the magnetic exchange and neutron diffraction data, we discuss the role of combined effects of crystalline electric field (CEF) perturbations and dilution in the evolution of magnetic properties with Y and La contents. In particular, we found negligible variations of the Bnm parameters along the Y series. The decrease of TN with x is fully dominated by magnetic dilution effects.

Effects of crystalline electronic field and onsite interorbital interaction in Yb-based quasicrystal and approximant crystal

To get an insight into a new type of quantum critical phenomena recently discovered in the quasicrystal Yb15Al34Au51 and approximant crystal (AC) Yb14Al35Au51 under pressure, we discuss the property of the crystalline electronic field (CEF) at Yb in the AC and show that uneven CEF levels at each Yb site can appear because of the Al/Au mixed sites. Then we construct the minimal model for the electronic state on the AC by introducing the onsite Coulomb repulsion between the 4f and 5d orbitals at Yb. Numerical calculations for the ground state shows that the lattice constant dependence of the Yb valence well explains the recent measurement done by systematic substitution of elements of Al and Au in the quasicrystal and AC, where the quasicrystal Yb15Al34Au51 is just located at the point from where the Yb-valence starts to change drastically. Our calculation convincingly demonstrates that this is indeed the evidence that this material is just located at the quantum critical point of the Yb-valence transition.

(BEDT-TTF)(TCNQ)結晶FETの電界効果移動度にみられる多段階相転移(発光・表示記録用有機材料およびデバイス・一般)

(BEDT-TTF)(TCNQ)結晶FETの電界効果移動度にみられる多段階相転移(発光・表示記録用有機材料およびデバイス・一般)

Characteristics of H-terminated single crystalline diamond field effect transistors

Diamond has been considered as an ultimate semiconductor, which has great potential applications in high power, high frequency semiconductor devices. Up to now, the twodimensional hole gas (2DHG) induced on the hydrogenterminated diamond surface is used most popularly to form electric conduction in diamond semiconductor at room temperature, due to the obstacle caused by lacking of easily-ionized dopants. A 200-nm-thick single crystalline diamond is grown by microwave plasma chemical vapor deposition on the type-Ib high-pressure high-temperature synthesized diamond substrate. Then the sample is treated in hydrogen plasma atmosphere to achieve hydrogen terminated diamond surface. The sample is characterized by X-ray photoelectron spectroscopy and atomic force microscope. After that, the normally-on hydrogen-terminated diamond field effect transistors are achieved. The device with a gate length of 2 μup m delivers a saturation leakage current of 96 mA/mm at gate voltage VGS=-6 V, at which, however, the gate leakage current is too large. The saturation current reaches 77 mA/mm at VGS=-3.5 V with safety. The device shows typical long-channel behavior. The gate voltage varies almost linearly. In the saturation region of the device, the transconductance (gm) increases near-linearly to 30 mS/mm with the increase of the gate voltage in a range of 5.9 V. Analyses of the on-resistance and capacitance-voltage (C-V) data show that the 2DHG under the gate achieves a density as high as 1.99×1013 cm-2, and the extracted channel carrier density and mobility are always kept increasing with VGS negatively shifting to -2.5 V. The nearlinearly increasing of gm in a large VGS range is attributed to high 2DHG density, quite a large gate capacitance (good gate control), and increased mobility. The relevant researches of improving the carrier mobility in the channel and of finding proper gate dielectrics to improve the forward gate breakdown voltage are underway.

Thermal and electron transport properties of Ce2Ni3Ge5 and Ce3NiGe2: Example of Kondo behavior in the presence of the crystalline field effect

Thermal and electron transport properties of the two Kondo compounds Ce2Ni3Ge5 and Ce3NiGe2 and of their nonmagnetic reference compounds La2Ni3Ge5 and La3NiGe2 were investigated by measurements of the thermoelectric power S, thermal conductivity κ, and electrical resistivity ρ. The effects of an applied magnetic field on the thermal and electron transport properties of both Ce compounds were examined. The temperature dependences of the 4f electron contribution to the electrical resistivity ρ4f, thermoelectric power S4f, and thermal resistivity W4f ·T exhibited −lnT behavior in two different temperature regions, which indicates that Ce2Ni3Ge5 and Ce3NiGe2 can be classified as Kondo systems with strong crystal-electric field (CEF) interactions. The total measured κ of Ce2Ni3Ge5 and Ce3NiGe2 was reduced compared with that of reference La compounds owing to the Kondo effect on Ce3+ ions. Within the framework of the Callaway model, the lattice component of thermal conductivity κph of both Ce compounds was analyzed while considering various relaxation processes governed by the scattering of phonons.

Phase diagram and collective excitations in an excitonic insulator from an orbital physics viewpoint

Excitonic insulating system is studied from the viewpoints of the orbital physics in strongly correlated electron systems. An effective model Hamiltonian for low-energy electronic states is derived from the two-orbital Hubbard model with a finite energy difference corresponding to the crystalline field splitting. The effective model is represented by the spin operators and the pseudo-spin operators for the spin-state degrees of freedom. The ground state phase diagram is analyzed by the mean-field approximation. In addition to the low-spin state and high-spin state phases, two kinds of the excitonic insulating phases emerge as a consequence of the competition between the crystalline field effect and the Hund coupling. The excitonic transition is classified to be an Ising-like transition reflecting a spontaneous breaking of the $Z_2$ symmetry. Magnetic structures in the two excitonic insulating phases are different from each other; an antiferromagnetic order and a spin nematic order. Collective excitations in each phase are examined by using the generalized spin-wave method. The Goldstone modes in the excitonic insulating phases appear in the dynamical correlation functions for the spins and pseudo-spin operators. Both the transverse and longitudinal spin excitation modes are active in the two excitonic insulating phases in contrast to the low-spin state and high-spin state phases. Connections of the present results to the perovskite cobalt oxides are discussed.

Antiferromagnetism and superconductivity in the half-Heusler semimetal HoPdBi

We observed the coexistence of superconductivity and antiferromagnetic order in the single-crystalline ternary pnictide HoPdBi, a plausible topological semimetal. The compound orders antiferromagnetically at TN = 1.9 K and exhibits superconductivity below Tc = 0.7 K, which was confirmed by magnetic, electrical transport and specific heat measurements. The specific heat shows anomalies corresponding to antiferromagnetic ordering transition and crystalline field effect, but not to superconducting transition. Single-crystal neutron diffraction indicates that the antiferromagnetic structure is characterized by the propagation vector. Temperature variation of the electrical resistivity reveals two parallel conducting channels of semiconducting and metallic character. In weak magnetic fields, the magnetoresistance exhibits weak antilocalization effect, while in strong fields and temperatures below 50 K it is large and negative. At temperatures below 7 K Shubnikov-de Haas oscillations with two frequencies appear in the resistivity. These oscillations have non-trivial Berry phase, which is a distinguished feature of Dirac fermions.

High performance single crystalline PbWO4 nanorod field effect transistor

The highly crystalline PbWO4 nanorods were synthesized using simple co-precipitation method which has application in field effect transistor. The synthesized PbWO4 nanorods were characterized by XRD, Raman spectroscopy, TEM and HRTEM indicating highly crystalline nature. Field effect transistor was fabricated on pre-patterned 300 nm SiO2/Si substrates using photolithography technique with channel length 1 µm and width 20 µm. Thin film (~100 nm) was made up of PbWO4 nanorods by spin coating on the pre-patterned device used as channel layer. The field effect mobility was observed to be 4.7 cm2 V−1 s−1 and ION/OFF ratio ~103 which is far better than the organic molecules due to single crystalline nature and rod like morphology of the PbWO4 providing direct path for charges to transport towards channel.

A direct route for the investigation of crystalline field effects on the spectral properties of Eu3+ ions in designed nanostructures

The spectral properties of lanthanide ions doped in a solid-state matrix, especially the Stark splitting and emission shifts, are strongly influenced by the local crystalline field. Here, we use a direct approach to quantitatively investigate the crystalline field effect on these spectral properties of Eu3+ ions in our designed β-PbF2:Eu3+ and BaF2:Eu3+ nanostructures. The extremely similar structures in which the central Eu3+ ions have the same site symmetry allow the local crystalline field to be simplified as the same point charge electrostatic field model. In this model, the direction and intensity of the electrostatic field are related to the distortion and expansion degree of the charge cloud of the luminescent center, respectively, and further determine the Stark splitting and emission shift. The theoretical analysis and charge-cloud stimulations were in good agreement with the experimental results. The direction and intensity of the crystalline field were calculated, and showed that the emission spectra shift to red with the increase in intensity. This work provides a comprehensive understanding of the spectral changes induced by a crystalline field, which is of great significance for the design of materials with the desired spectral properties.

Heavy fermion Ce3Co4Sn13 compound under pressure

The non-magnetic heavy fermion compound Ce3Co4Sn13 was studied under pressure. We report single crystalline measurements of electrical resistivity as a function of temperature ρ(T) under pressure. Some characteristic features related to a structural transition (TS), crystalline field effects (TCEF), and a low temperature maximum (Tmax), possibly connected simultaneously to the onset of Kondo lattice coherence and short range magnetic correlations, were identified in the ρ(T) data. A pressure-temperature phase diagram with TS and Tmax was constructed by mapping these features. Like for most Ce-based heavy fermion compounds, Tmax moves to higher temperatures with pressure, indicating that it is related to the Kondo energy scale, due to the increase of hybridization induced by pressure. On the other hand, TS, associated to a superlattice distortion and probably combined with a charge density wave transition, decreases as a function of pressure. However, differently from the Sr3−xCaxIr4Sn13 system, where a superlattice quantum phase transition is observed [L. E. Klintberg et al., Phys. Rev. Lett. 109, 237 008 (2012)], in Ce3Co4Sn13 TS ∼ 154 K, at ambient pressure (P = 0), seems to stabilize at around 143 K for P ≥ 19 kilobars. We also investigated ρ(T) in external magnetic fields, at P = 0. Negative magnetoresistance and increase of Tmax are observed, suggesting suppression of low temperature short range magnetic correlations.

Raman Spectroscopic Studies on L-histidine, aniline Doped Triglycine Sulphate Single Crystals

Single crystals of triglycine sulphate (TGS) doped with L-histidine and aniline were studied by Raman Spectroscopy. The structure and symmetry of molecules, the nature of bonding and the effect of crystalline field on molecular vibrations were studied for pure and doped TGS. The characteristic group frequencies were identified and analysed for H2SO4 and glycine. The skeletal motion, lattice vibrational peaks were observed in the low wavenumber region. The site symmetry effect and the correlation field effect were studied from the splitting of vibrational bands. The observed Raman shift towards higher wave number region reveals that the symmetry reduction in doped TGS crystals. The broadening of Raman spectral line showed that a decrease in the hardness value for the doped crystals. Comparative studies of the Raman Spectra of pure TGS and doped TGS were also carried out.

A normally-off microcontroller unit with an 85% power overhead reduction based on crystalline indium gallium zinc oxide field effect transistors

A low-power normally-off microcontroller unit (NMCU) having state-retention flip-flops (SRFFs) using a c-axis aligned crystalline oxide semiconductor (CAAC-OS) such as indium gallium zinc oxide (IGZO) transistors and employing a distributed backup and recovery method (distributed method) is fabricated. Compared to an NMCU employing a centralized backup and recovery method (centralized method), the NMCU employing the distributed method can be powered off approximately 75 µs earlier after main processing and can start the main processing approximately 75 µs earlier after power-on. The NMCU employing the distributed method can reduce power overhead by approximately 85% and power consumption by approximately 18% compared to the NMCU employing the centralized method. The NMCU employing the distributed method can retain data even when it is powered off, can back up data at high speed, and can start effective processing immediately after power-on. The NMCU could be applied to a low-power MCU.

Magnetic phase transition and magnetocaloric effect in Dy12Co7 compound

Magnetic and magnetocaloric properties of Dy12Co7 compound have been investigated by magnetization measurements. Its magnetization does not reach saturation even for 7 T at 2 K due to the crystalline field effect. Dy12Co7 undergoes a ferromagnetic-paramagnetic phase transition around Curie temperature TC = 64 K. The thermomagnetic irreversibility between the zero-field-cooling and field-cooling curves is detected below TC in low magnetic field, and it is attributed to the narrow domain wall pinning effect. Large magnetic entropy change of 10.0 J kg−1 K−1 and refrigerant capacity of 299 J kg−1 for a magnetic field change of 0–5 T are found around TC, resulting from the large change of magnetization during the magnetic phase transition. The nature of second-order phase transition for Dy12Co7 induces the complete reversibility of magnetic entropy change around TC, which is very favourable for the application of magnetic refrigeration.