Equal Random Crystal Field of Mixed Spin-1 and Spin-3/2 System

The mixed spin-1 and spin-3/2 Ising system is investigated on the Bethe lattice at random distribution of crystal field which are taken equal at both spin sites. The investigations of thermal variations of the sublattice, net and average magnetizations have revealed that the system gives three compensation temperatures in contrary to the literature where only two of them are mentioned so far. The phase diagrams of the random crystal field case with probability p are also calculated at the range of 0 ≤ p < 1.0. It is found that in this range for equal crystal field case, the tricritical points disappear and only the second-order phase transitions are exhibited which is opposite to the case p = 1.0. In addition, we have also classified the thermal variations of average magnetizations according to the Néel nomenclature.     

Hexagonal-Type Ising Nanowire with Core/Shell Structure Designed with Half-Integer Spins: Compensation Behaviors and Phase Diagrams in the Temperature and Interaction Planes

The effective field theory with correlation is used to investigate the magnetic behaviors of the mixed spin-1/2 and spin-3/2 hexagonal Ising nanowire (HIN) with core/shell in the crystal field. The total magnetization as a function of the temperature is used to describe the compensation behaviors of the system, and the N-, Q-, P-, R-, and S-type compensation types are given. The dependence of the phase diagrams on interaction parameters is studied in detail and presented the phase diagrams in the six different planes, namely (J ₁, Δ, T), (J _C, Δ, T), (J _S, Δ, T), (J ₁, J _C, T), (J ₁, J _S, T) and (J _C, J _S, T).Besides, the system exhibit second-order phase transition and first-order phase transitions, which can be found via the variations of the total magnetization with the crystal field in the mixed spin-1/2 and spin-3/2 HIN.     

Spin Compensation Temperatures in the Monte Carlo Study of a Mixed Spin-3/2 and Spin-1/2 Ising Ferrimagnetic System

The magnetic properties of mixed-spin S ^′ = 3/2 and S = 1/2 ferrimagnetic system have been studied by Monte Carlo simulations. The ground-state phase diagrams of mixed spin-3/2 and spin-1/2 Ising system are given. The critical and compensation temperatures have been found with different values of reduced exchange interactions. The variation of total magnetization with reduced exchange interactions of mixed spins is given with different temperatures and crystal fields. We have also given the variation of total magnetization with crystal field for different reduced exchange interactions and different temperatures. The magnetic hysteresis cycle is found to have different values of reduced exchange interactions, temperatures, and crystal fields. The multiple hysteresis and the superparamagnetic phase are established.     

Dynamic Magnetic Hysteresis Behaviors in a Mixed Spin (3/2, 2) Bilayer System with Different Crystal-Field Interactions

Dynamic magnetic hysteresis (DMH) behaviors of the mixed spin-3/2 and spin-2 Ising bilayer system with different crystal-field interactions on a two-layer square lattice is studied by the use of dynamic mean field calculations based on the Glauber-type stochastic. The hysteresis loops are obtained for different reduced temperatures (T), magnetic field amplitudes (h), frequencies (w) and interlayer coupling constants (J ₃). Influences of the T, h, w and J ₃ on the DMH properties are investigated. We also study the temperature, frequency and interlayer coupling interaction dependence of the coercive field and remanent magnetization. We compare our results with some theoretical and experimental works and observe a quantitatively good agreement with some theoretical and experimental results.     

The Random <Emphasis Type="Italic">J</Emphasis>-Model with Biquadratic Interaction

The spin-1 model is studied on the Bethe lattice by including the bilinear J and biquadratic K exchange interactions into the Hamiltonian. The effects of J is randomized by using a bimodal random distribution with an adjustable parameter α which allows to study the cases of ±J-model and bond-dilution. The thermal variations of the order-parameters are studied to obtain the possible phase diagrams of the model. It is found that second-order phase transitions lines separate the ordered-phases, ferromagnetic, or antiferromagnetic, from the disordered one, i.e., the paramagnetic phase. The staggered quadrupolar phase lines are also found and only seen for higher negative K values for coordination number q=4 and 6, only. The reentrant behavior is also found for some of the phase transitions lines.     

Magnetic Nanoparticle Systems: Dendrimer Model

The aim of this study is to determine and interpret the magnetic properties of a dendrimer nanoparticle system. In this model, we are inspired by a system with core-shell spins σ = 3 and S = 7/2 as the elements of this model. We first examine the ground-state phase diagrams, which are followed by the elaboration and discussion of the stable phases. Then, a theoretical study by Monte Carlo simulations (MCSs), in the framework of the Ising model, is elaborated to investigate this system. By doing so, a number of results are achieved, namely the reduced critical temperature that is determined ( T _c / J _{σ σ} ) through studying the total and partial magnetizations and susceptibilities as a function of the temperature. Then, the effects of the crystal field on the total magnetizations, for the different values of the reduced exchange coupling and the reduced external magnetic field, are explored and discussed. Finally, the hysteresis loop behaviors are established and discussed.     

Random Crystal Field in a Mixed Spin <Emphasis Type="Italic">S</Emphasis> = 1/2 and <Emphasis Type="Italic">S</Emphasis> = 3/2 Ising Model by Renormalization Group Theory

In this work, we study the Ising model with mixed spins S = ?1/2 and S = ?3/2 on the hypercubic lattice and the random crystal field at the sublattice with S =?3/2 described by a two peaks law. To achieve this, we use an approximation of position space renormalization group (PSRG) namely Migdal-Kadanoff in which we use both the free energy derivative and the flow in the parameter space of the Hamiltonian. For all values of the random probability, the critical behavior is determined via the critical exponents at the second-order fixed points while at low temperatures; the discontinuities of the of the free energy derivative provide the positions of the first-order transitions. The introduction of a minimal amount of disorder causes a change in the phase diagram showing the relevance of disorder for d =?2 and d =?3. The second-order transition remains always with the same critical exponents as those of the pure model, and a new first-order transition appears at very low temperature. Also, a comparison with other similar works is given.     

Dynamics of Spinor Condensates Driven by an Inhomogeneous Magnetic Field

A variational wavefunction including the breather, dipole and scissor modes simultaneously is constructed to investigate the collective-excitation dynamics of spin-1 \(^{87}\mathrm{Rb}\) condensates driven by a space- and time-dependent magnetic field. When the Dirac point never enters the condensate, it is shown that the dipole, breather and scissor modes will be all excited driven by the sinusoidal oscillation of the Dirac point, due to the coupling of different collective modes from the inhomogeneity of the magnetic field. A resonance-driving phenomenon is observed. If the Dirac point passes through the condensate, our numerical results agree with most experimental observations (Ray et al. in Nature 505:657, 2014) and find that the center of mass of the condensate does not follow the zero point of the magnetic field. Hopefully, our method can be extended to study the similar dynamics for the other spinor condensates.     

Long-Range Spin-Triplet Superconductivity Induced by Magnetic Field in d Wave Superconductor/Ferromagnet Hybrid System

We theoretically study the long-range spin- triplet superconductivity in d wave superconductor/ ferromagnet/ferromagnet (S/F₁/F₂) trilayer junction, in which the magnetization of F₁ layer could be rotated in the y–z plane by an external magnetic field. The four-component Eilenberger equations were constructed to calculate the superconducting order parameters and density of states (DOS). Near the clean limit, the p wave equal-spin triplet component could be induced when the magnetization directions of F₁/F₂ layers are non-collinear, and the DOS exhibits a split zero-bias conductance peak. The various parameters such as ferromagnetic exchange energy, thickness of ferromagnetic layers, and angles between F₁/F₂ magnetization directions are studied for the effect on inducing triplet superconductivity. By magnetic field controlling the emergence of equal-spin triplet pairings or not, such a tunable S/F₁/F₂ trilayer junction based on long-range spin-triplet superconductivity could be used as a superconducting switch device, which would open up a new view of spintronics.     

Crystal Growth and Magneto-transport of Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript> Single Crystals

In this letter, we report on the growth and characterization of bulk Bi ₂Se ₃ single crystals. The studied Bi ₂Se ₃ crystals are grown by the self-flux method through the solid-state reaction from high-temperature (950 °C) melt of constituent elements and slow cooling (2 ℃/h). The resultant crystals are shiny and grown in the [00l] direction, as evidenced from surface XRD. Detailed Reitveld analysis of powder X-ray diffraction (PXRD) of the crystals showed that these are crystallized in the rhombohedral crystal structure with a space group of R3m (D5), and the lattice parameters are a = 4.14 (2), b = 4.14 (2), and c = 28.7010 (7) Å. Temperature versus resistivity (ρ?T) plots revealed metallic conduction down to 2 K, with typical room temperature resistivity (ρ _{300 K}) of around 0.53 m Ω-cm and residual resistivity (ρ _{0 K}) of 0.12 m Ω-cm. Resistivity under magnetic field [ ρ(T)H] measurements exhibited large + ve magneto-resistance right from 2 to 200 K. Isothermal magneto-resistance [ ρH] measurements at 2, 100, and 200 K exhibited magneto-resistance (MR) of up to 240 %, 130 %, and 60 %, respectively, at 14 T. Further, the MR plots are nonsaturating and linear with the field at all temperatures. At 2 K, the MR plots showed clear quantum oscillations at above say 10 T applied field. Also, the Kohler plots, i.e., Δρ/ ρ _oversus B/ ρ, were seen consolidating on one plot. Interestingly, the studied Bi ₂Se ₃ single crystal exhibited the Shubnikov-de Haas (SdH) oscillations at 2 K under different applied magnetic fields ranging from 4 to 14 T.     

Superconductor-Semiconductor Metamaterial Photonic Crystals

We constructed theoretically one-dimensional photonic crystal (1DPC) by using a semiconductor metamaterial in the near-infrared range(NIR) which is composed of Al-doped Z n O(A Z O) and Z n O. The construction of this photonic crystal (PC) is based on a high-temperature superconductor material with the semiconductor metamaterial as constituent layers for this PC. The electromagnetic interactions with this periodic structure are investigated using the transfer matrix method (TMM) in the NIR range. The investigation shows that the reflectance spectra are depending on some parameters of the periodic structure such as the thicknesses of the constituent layers, temperature, and the angle of incidence.     

In-field Conductivity Fluctuations in Ba<Subscript>0.72</Subscript>K<Subscript>0.28</Subscript>Fe<Subscript>2</Subscript>As<Subscript>2</Subscript> Single Crystals

Fluctuations in the conductivity of Ba_0.72K_0.28Fe₂As₂ single crystal are studied systematically by resistance measurements as a function of temperature and magnetic field. A clear Maki?Thompson and Aslamakov?Larkin (MT–AL) two- to three-dimensional (2D–3D) crossover is found on the excess conductivity (Δσ) curves as the temperature approaches the superconducting critical temperature, T _c. 3D fluctuations in superconductivity are realized near T _c that are well fitted to experimental data by the 3D Aslamazov–Larkin theory. The Maki–Thompson model shows a 2D conductivity fluctuation above the 2D-3D temperature transition, T ₀, which depends on magnetic field. Results show that the 2D-3D dimensional crossover moves to lower temperature with increasing magnetic field. The values of the transition temperature and the crossover in the reduced temperature, ln(ε ₀), as functions of magnetic field were used to determine the coherence length and the lifetime, τ _φ , of the fluctuational pairs at the temperature of 35 K. Analysis of the Ba_0.72K_0.28Fe₂As₂ single crystal gives a value of 3.76 × 10^??12 s for the τ _φ in the absence of magnetic field and it decreases to 2.4 × 10^??12 s in magnetic field of 13 T.     

Dependence of the low-temperature specific heat of YBa2Cu3O7−δ on δ and magnetic field: Concentrations of spin-2 and spin-1/2 paramagnetic centers

Specific heat data on two samples of YBa₂Cu₃O_7– with relatively low concentrations of paramagnetic centers show the presence of both spin-2 and spin-1/2 moments. Measurements on one sample following incremental increases in show that for 0.2 approximately one spin-1/2 moment is produced for each 100 O vacancies, with no substantial increase in the linear term of the specific heat. For several reasons it is concluded that these O-vacancy related moments are different from those that have figured in previously reported correlations with parameters characteristic of the superconductivity.     

Giant Magnetoresistance in Topological Insulator Bi<Subscript>1.98</Subscript>Nd<Subscript>0.02</Subscript>Se<Subscript>3</Subscript> Single Crystal

Doped topological insulators (TI) Bi_2?x Nd _x Se₃ single crystals were prepared by the self-flux method. The phase structure, magnetic properties, and electrical transport properties of the samples were studied. The X-ray diffraction (XRD) patterns of the sample indicate an incorporation of Nd into the Bi₂Se₃, and the crystal can be easily cleaved with silvery surface. The Bi_2?x Nd _x Se₃ sample shows a giant magnetoresistance (MR) with different magnetic field. The positive magnetoresistance (MR) can reach 190 % at the field of 9 Tesla when the field is perpendicular to ab-plane of the crystal. In addition, at low magnetic fields, the MR exhibits a weak antilocalization (WAL) cusp.     

Triangular Ising Ferromagnet with Mixed Spins (<Emphasis Type="Italic">A</Emphasis> = 1/2, <Emphasis Type="Italic">B</Emphasis> = 1/2, <Emphasis Type="Italic">C</Emphasis> = 1): Dynamic Magnetic Properties and Hysteresis Curves

The dynamic properties of the triangular Ising ferromagnet consisting of the mixed spins A = 1/2, B = 1/2, and C = 1 is studied by using the mean-field theory (MFT) as well as Glauber-type stochastic dynamics (GSD). The coupling equations to investigate dynamic behaviors of the system are calculated, and phase transitions, phase diagrams, and hysteresis curves are obtained. From these studies, first- and second-order transition lines, the dynamic phase diagrams (DPDs) in the (T,h ₀) and (T,d) planes, and single hysteresis curves are presented. In the DPDs, dynamic tricritical point due to the first- and second-order phase transitions are observed. It is found that the dynamic hysteresis properties of the triangular system strongly depend on the temperature and crystal field.     

Study of Half-Metallic Ferromagnetism in Be0.75Ti0.25Y (Y = S,Se, and Te) Using Ab Initio Calculations: Potential Candidate for Spintronic Devices

The structural, elastic, electronic, and magnetic properties of Be_0.75Ti_0.25Y (Y = S, Se, and Te) have been investigated to understand their potential applications in spintonic devices. Crystals of BeS, BeSe, and BeTe, individually doped with Ti with a dopant concentration of x = 0.25, have been evaluated by using full-potential linearized augmented plane-wave plus local orbital method within the framework of density functional theory. We employed the Wu–Cohen generalized gradient approximation for optimizing the crystal structure and evaluating elastic properties. In order improve bandgap values and optical parameters, the modified Becke and Johnson (mBJ) potential has been employed. The theoretical investigation of band structure and density of states confirms the half-metallic ferromagnetic nature of these compounds. The elastic constants are calculated by the charpin method which shows that the compounds under consideration are brittle and anisotropic. Moreover, it is noted that tetrahedral crystal field splits the 3d state of Ti into triple degenerate t_2g and double degenerate e_g states. The exchange splitting energies Δ _x (d) and Δ _x (pd) and exchange constants (N ₀ α) and (N ₀ β) are predicted from triple degenerate t_2g states, and negative values of N ₀ β justify that the nature of effective potential is more attractive in spin down case rather than that in the spin up case. We also find the crystal field splitting (ΔE _crystal = E _t2g?E _eg) energy and reduction of the local magnetic moment of Ti from its free space charge value and creation of small local magnetic moments on the non-magnetic Be, S, Se, and Te sites by p–d hybridization.     

Novel Solid-State Growth of <Emphasis Type="Italic">p</Emphasis>-Terphenyl: the Parent High-<Emphasis Type="Italic">T</Emphasis><Subscript>c</Subscript> Organic Superconductor (HTOS)

We report an easy and versatile route for the synthesis of the parent phase of the newest superconducting wonder material, i.e., p-terphenyl. Doped p-terphenyl has recently shown superconductivity with transition temperature as high as 120 K. For crystal growth, the commercially available p-terphenyl powder is pelletized, encapsulated in an evacuated (10^?4 Torr) quartz tube and subjected to high-temperature (260 ^°C) melt followed by slow cooling at 5 ^°C/h. A simple temperature-controlled heating furnace is used during the process. The obtained crystal is one piece, shiny, and plate like. Single crystal surface XRD (X-ray diffraction) showed unidirectional (00l) lines, indicating that the crystal is grown along the c-direction. Powder XRD of the specimen showed that as grown p-terphenyl is crystallized in monoclinic structure with space group P2 ₁/a space group, having lattice parameters a = 7.672 (2) Å, b = 5.772 (5) Å, and c = 13.526(3) Å and β = 91.484 (3)^°. Scanning electron microscopy (SEM) pictures of the crystal showed clear layered slab-like growth without any visible contamination from oxygen. Characteristic reported Raman active modes related to C–C–C bending, C–H bending, C–C stretching, and C–H stretching vibrations are seen clearly for the studied p-terphenyl crystal. The physical properties of the crystal are yet underway. The short letter reports an easy and versatile crystal growth method for obtaining quality p-terphenyl. The same growth method may probably be applied to doped p-terphenyl and to subsequently achieve superconductivity to the tune of as high 120 K for the newest superconductivity wonder, i.e., high- T _c organic superconductor (HTOS).     

Dislocation Mobility and Anomalous Shear Modulus Effect in $$^$$He Crystals

We calculate the dislocation glide mobility in solid \(^4\)He within a model that assumes the existence of a superfluid field associated with dislocation lines. Prompted by the results of this mobility calculation, we study within this model the role that such a superfluid field may play in the motion of the dislocation line when a stress is applied to the crystal. To do this, we relate the damping of dislocation motion, calculated in the presence of the assumed superfluid field, to the shear modulus of the crystal. As the temperature increases, we find that a sharp drop in the shear modulus will occur at the temperature where the superfluid field disappears. We compare the drop in shear modulus of the crystal arising from the temperature dependence of the damping contribution due to the superfluid field, to the experimental observation of the same phenomena in solid \(^4\)He and find quantitative agreement. Our results indicate that such a superfluid field plays an important role in dislocation pinning in a clean solid \(^4\)He at low temperatures and in this regime may provide an alternative source for the unusual elastic phenomena observed in solid \(^4\)He.     

Density estimation for spatial-temporal models

In this paper a k-nearest neighbor type estimator of the marginal density function for a random field which evolves with time is considered. Considering dependence, the consistency and asymptotic distribution are studied for the stationary and nonstationary cases. In particular, the parametric rate of convergence $\sqrt{T}$ is proven when the random field is stationary. The performance of the estimator is shown by applying our procedure to a real data example.     

Control of Both Superconducting Critical Temperature and Critical Current by Means of Electric-Field-Induced Reconfigurable Strain

The controlled modification of superconductivity by any means is a long-standing issue in low-temperature physics. In this work, we present data on the control of the superconducting properties of conventional low critical-temperature (T_C) Nb thin films with thickness (d_Nb) =?15 and 20 nm under application of reconfigurable strain, S induced by an external electric field, and E_ex to a piezoelectric (PE) single crystal, namely (1 ? x)Pb(Mg_1/3Nb_2/3)O₃ ? x PbTiO₃ (PMN-PT) with x =?0.30–0.31. The experimental results (reduction of T_C and critical current (J_C) on the order of 6% and 90–100%, respectively) are nicely reproduced with a phenomenological model that incorporates the constitutive relation S(E_ex) that describes the electro-mechanical response of the PE crystal to well-established formulas that describe T_C and J_C of the SC thin films.