Dependence Of Critical Field Research Articles

Calculation of temperature dependent critical field strength of mixtures containing C5-FK, CO 2 and O 2

Calculation of temperature dependent critical field strength of mixtures containing C5-FK, CO ₂ and O ₂

A tool for identifying the criticality in the disordered systems with metastable dynamics

We tackle the question of criticality in disordered systems that exhibit metastable dynamics throughout the process of relaxation. We propose a tool for discovering the existence of nontrivial critical behaviour and showcase it on the nonequilibrium athermal random field Ising model, being a pivotal example of the nonequilibrium models of disordered systems. By this tool, we analysed the dependence of critical field on the disorder of the system using different initial setups, the traditional with all spins pointing downwards and those modified which consider the lattice having an interface of aforehand preset upward spins at some cross-section and the others having islands of preset upward spins with diameters smaller than the lattice size. Our results obtained in this way on the cubic three-dimensional, square two-dimensional and hexagonal two-dimensional lattices are in agreement with those found by traditional methods which evidences the applicability of the proposed tool.

Magnetic properties of dysprosium – Experiment and modeling

Here we present the continuation of the approach developed in our previous work [1] taking another lanthanide metal – Dy – as an example. The rich set of the experimental data which includes data on magnetization (field and temperature dependencies), magnetic susceptibility, heat capacity, magnetocaloric effect and, finally, the critical field dependence on temperature (phase diagram) allows performing the thorough comparison of experimental and modeling results within the molecular field method. An effective field used in the calculations takes a six-fold temperature dependent anisotropy energy, first and second neighbor exchange and Zeeman energy into account. Such an approach allows not only to underline the common trends for the whole lanthanide series taking Tb, Ho and Dy (in this paper) as examples but also partly eliminate the limitations of ab initio calculation in case of 4f elements.

Experimental evidence of a very thin superconducting layer in epitaxial indium nitride

Indium nitride is one of the very few semiconductors which is known to have a superconducting phase at temperatures of Tc > 1 K. Superconductivity occurs in a window of carrier densities of approximately 1018–1020 cm−3. This is a very low density when compared to other superconductors (i.e. metals, alloys, high Tc oxides) and thus raises interesting fundamental questions as well as technological possibilities. In this paper we address one key question about the dimensionality of the superconducting state of InN by using angle dependent critical field measurements. Our samples were grown by two different growth techniques (chemical vapour deposition and plasma-assisted molecular beam epitaxy) on c-oriented sapphire, with and without a GaN buffer layer. In both cases we find that for film thicknesses much larger than the coherence length d ≫ ξ, the angle dependence of the critical field (down to T < 280 mK) with respect to the c-axis continues to be clearly two-dimensional, demonstrating a characteristic cusp when the angle crosses 90° with respect to the c-axis. This indicates that the superconducting electrons are most likely confined to a layer much thinner than the thickness of the InN film. Further we find the magnitude of the gap to be 2Δ(0)/kBTc = 3.6, very close to the BCS prediction.

Magnetic properties of type-I and type-II Weyl semimetals in the superconducting state

Superconductivity was observed in certain range of pressure and chemical composition in Weyl semi-metals of both the type I and type II (when the Dirac cone tilt parameter $\kappa >1$). Magnetic properties of these superconductors are studied on the basis of microscopic phonon mediated pairing model. The Ginzburg - Landau effective theory for the order parameter is derived using Gorkov approach and used to determine anisotropic coherence length, the penetration depth determining the Abrikosov parameter for a layered material and applied to recent extensive experiments on $% MoTe_{2}$. It is found that superconductivity is of second kind near the topological transition at $\kappa =1$, but becomes first kind away from it. For the superconductors of the second kind the dependence of critical fields $H_{c2}$ and $H_{c1}$ on the tilt parameter $\kappa $ (governed by pressure) is compared with the experiments. Strength of thermal fluctuations is estimated and its is found that they are strong enough to cause Abrikosov vortex lattice melting near $H_{c2}$. The melting line is calculated and is consistent with experiments provided the fluctuations are three dimensional in the type I phase (large pressure) and two dimensional in the type II phase (small pressure).

Unusual superconducting behavior in HfV2Ga4

Bulk superconductivity in HfV2Ga4 with critical temperature close to 4.1 K was determined via magnetic susceptibility, electrical resistivity and specific heat measurements. Both the upper and lower critical field dependence with reduced temperature (T/Tc) exhibit non-conventional behavior. The electronic component of specific heat shows a double-jump, the first close to Tc and the other close to 0.75Tc. We speculate about the nature of the douple jump observed in specific heat considering two plausable scenarios: bulk inhomogeneities and the existence of a second gap.

Total Internal Reflection in a Hybrid Nematic Cell Submitted to Weak Boundary Conditions

We calculate the trajectory of a monochromatic optical beam propagating in a planar-homeotropic hybrid nematic crystal cell submitted to weak anchoring conditions. We apply a uniform electric field perpendicular to the cell to control the trajectories for various values of the anchoring elastic energy. We have found that the anchoring energy has a strong influence on the ray penetration length and trajectory. Our calculations are consistent with a previously found Frederick’s type transition only present for weak anchoring in which electric fields above an anchoring-energy dependent critical field align completely the director field.

Increased upper critical field for nanocrystalline MoN thin films deposited on AlN buffered substrates at ambient temperature

Molybdenum nitride (MoN) thin films have been deposited using reactive DC magnetron sputtering on aluminum nitride buffered oxidized silicon substrates at ambient temperature. GIXRD of aluminum nitride (AlN) deposited under similar conditions has revealed the formation of wurtzite phase AlN. GIXRD characterization of molybdenum thin films deposited on AlN buffered oxidized silicon substrates has indicated the formation of nanocrystalline MoN thin films. The electrical resistivity measurements indicate MoN thin films have a superconducting transition temperature of ~8 K. The minimum transition width of the MoN thin film is 0.05 K at 0 T. The inferred upper critical field Bc2(0) for these nanocrystalline MoN thin films obtained by fitting the temperature dependence of critical field with Werthamer, Helfand and Hohenberg theory lies in the range of 17–18 T which is the highest reported in literature for MoN thin films.

Electric field induced orientational order of gold nanorods in dilute organic suspensions

The electric field controlled alignment of gold nanorods offers a paradigm for anisotropic molecules with the potential for a wide variety of phases and structures. We experimentally study the optical absorption from gold nanorod suspensions aligned using external electric fields. We show that the absorption from these suspensions depends linearly on the orientational order parameter. We provide evidence that the critical electric field needed to orient the gold nanorods is proportional to the nanorod volume and depolarization anisotropy. Utilizing this critical field dependence, we demonstrate for suspensions with two different nanorod sizes that the alignment of each population can be controlled. We also develop a technique to determine the imaginary parts of the longitudinal and transverse electric susceptibilities of the nanorods. The ability to selectively address specific parts of the nanorod populations in a mixture using external fields may have significant potential for future display and optical filter applications.

Strain Dependence of Critical Fields—Studied on Piezoelectric Substrates

<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$\hbox{La}_{{\kern-.5pt}1{\kern-.5pt}.{\kern-.5pt}85}{\kern-.5pt}\hbox{Sr}_{{\kern-.5pt} 0{\kern-.5pt}.{\kern-.5pt}15}{\kern-.5pt}\hbox{CuO}_{{\kern-.5pt}4}$</tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$\hbox{BaFe}_{{\kern-.5pt}1{\kern-.5pt}.{\kern-.5pt}8}{\kern-.5pt}\hbox{Co}_{{\kern-.5pt} 0{\kern-.5pt}.{\kern-.5pt}2}{\kern-.5pt}\hbox{As}_{{\kern-.5pt}2}$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$\hbox{FeSe}_{{\kern-.5pt}0{\kern-.5pt}.{\kern-.5pt}5}{\kern-.5pt}\hbox{Te}_{{\kern-.5pt}0.5}$ </tex-math></inline-formula> thin films have been prepared on piezoelectric (001) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$\hbox{Pb}(\hbox{Mg}_{1/3}\hbox{Nb}_{2/3})_{0.72}\hbox{Ti}_{0.28}\hbox{O}_{3}$</tex-math> </inline-formula> substrates. By the use of the inverse piezoelectric effect, biaxial strain was induced into the films by applying an electric field to the sample. The strain sensitivity of the upper critical field and of the irreversibility line was determined by the analysis of the resistive transition. A biaxial compression in the order of 0.02% results in a shift of these fields. A consistent description of the field dependence is possible taking into account a strain dependent transition temperature. No influence of the strain state on the anisotropy of the upper critical field was found in first approximation.

Size dependence of the magnetization reversal in a ferromagnetic particle

In this work the finite elements method is used to simulate by micromagnetic modelling the behavior of a spherical ferromagnetic particle with uniaxial magnetocrystalline anisotropy. Full magnetization loops are taken in the easy axis direction at different values of anisotropy constant and particle size. The results indicate reversal mechanisms such as the coherent rotation, the curling mode and the growth of a reverse magnetization domain. The size dependence of critical fields and of other magnetic parameters, such as the nucleation volume of the reverse domain, the domain wall width and the susceptibility, is presented.

Spin transfer torque generated magnetic droplet solitons (invited)

We present recent experimental and numerical advancements in the understanding of spin transfer torque generated magnetic droplet solitons. The experimental work focuses on nano-contact spin torque oscillators (NC-STOs) based on orthogonal (pseudo) spin valves where the Co fixed layer has an easy-plane anisotropy, and the [Co/Ni] free layer has a strong perpendicular magnetic anisotropy. The NC-STO resistance and microwave signal generation are measured simultaneously as a function of drive current and applied perpendicular magnetic field. Both exhibit dramatic transitions at a certain current dependent critical field value, where the microwave frequency drops 10 GHz, modulation sidebands appear, and the resistance exhibits a jump, while the magnetoresistance changes sign. We interpret these observations as the nucleation of a magnetic droplet soliton with a large fraction of its magnetization processing with an angle greater than 90°, i.e., around a direction opposite that of the applied field. This interpretation is corroborated by numerical simulations. When the field is further increased, we find that the droplet eventually collapses under the pressure from the Zeeman energy.

An Influence of Boundary Effects and Spatial Symmetry on Magnetization Reversal of Nanodisk Arrays

The effect of arrays' size on magnetization reversal in nanodisks has been investigated. Symmetrical arrays of Py nanodisks with diameter 600 nm and thicknesses 10, 22, and 30 nm has been studied by magneto-optical Kerr effect (MOKE) and magnetic force microscopy (MFM). It has been found that the increase in a number of nanodisks leads to the fall of magnetic vortex annihilation field. The dependence of the vortex nucleation field has oscillating behavior due to magnetostatic interaction between adjacent nanodisks. The dependences of critical fields of vortex nucleation and annihilation calculated within “rigid” vortex model are in a good agreement with experimental results. Using MFM it has been demonstrated that transition from single domain state to C-state occurs in nanodisks at different applied magnetic fields. We have revealed that the coincidence of magnetization switching in nanodisks rises with increasing of magnetostatic interaction.

Angular dependence and temperature effect on switching field distribution of Co/Pd based bit patterned media

The motivation for this work is rooted in the reversal process that occurs in perpendicularly magnetic Co/Pd multilayered based bit-patterned media. In our work, temperature effect and angle dependence of critical fields (Hcr) and switching field distribution (SFD) are studied by both experiment and simulation. From our observation, when temperature increases from 77 to 300 K, the critical field of patterned area decreases from 13 to 11 kOe. Absolute SFD decreases from 2.6 to 2.2 kOe as thermal energy assists islands reversal. The relative SFD (SFD/Hcr) keeps constant with temperature. Although critical fields and absolute SFD vary with angles, relative SFD is independent of the field angle. The interactions between islands broaden relative SFD from 12% to 20% after considering dipolar interactions. The relative SFD by simulation agrees well with our experimental observation.

Magnetodielectric response in the charge ordered oxyborate Fe2OBO3

We present a detailed investigation on the magnetodielectric properties of Fe2OBO3, where we have found a magnetodielectric effect around 150% at room temperature and ν=2 kHz, that cannot solely arise from magnetoresistive extrinsic contributions. In addition, we find a crossover of the magnetodielectric response around TN, that we attribute to changes in the electronic microstructure of this compound that take place at that temperature. For T&amp;lt;TN the dielectric constant experiences a jump at a temperature dependent critical field that we relate to a partial melting of the charge ordering state.

Superconducting Property and Strain Effect Study of the ${\rm Nb}_{3}{\rm Sn}$ Strands Developed for ITER

Japan Atomic Energy Agency has developed Nb3Sn strands for the ITER magnet, whose critical current density is about 1.4 times as large as that of ITER CS Model Coil. The magnetic field, temperature, and strain dependence on the critical current (Ic) of the strands were measured with apparatus that were developed by the authors. The strain properties in particular were investigated in detail, with strain tensor analysis revealing that the upper critical field dependence on strain can be naturally formulated using a high order polynomial terms of strain taking into account residual strain due to thermal contraction difference inside the strand and strain applied externally. A correlation formula for field, temperature, strain and Ic of the strand is discussed and presented. Recent results of fabricating strands for ITER TF coil are then finally provided.

Influence of nanoparticle doping on electronic properties of MgB2 bulk samples

Superconducting and normal-state properties of MgB2 polycrystalline samples with non magnetic (SiC) and magnetic (Co) dopant addition were analysed in order to study the doping influence on the magnetic anisotropy of MgB2 polycrystalline samples and to correlate this influence with the doping-induced changes in band scattering processes. Both doping typologies result in a decrease of the MgB2 upper critical field anisotropy factor. For SiC-doped samples this result is joined to an upper critical field (Bc2) shift toward higher temperatures whereas Co doped samples exhibit a Bc2 decrease. To guide the application road map a theoretical approach to the analysis of the normal state resistivities (SiC doping) and of the upper critical field dependence on temperature (SiC and Co dopings) was performed. According to this scenario, band scattering rate as well as electron diffusivity values obtained by these analyses showed for both the investigated doping typologies an increase of intraband scattering processes in the more anisotropic σ band whereas the conductivity of π band remains almost unaffected.

Carbon-doping effects on the metamagnetic transition and magnetocaloric effect in MnAsC x

Carbon doping effects in MnAs alloys have been investigated. More carbon doping in MnAs alloys leads to lower Curie temperature, larger thermal hysteresis and sharper slope of the dependence of critical field on reduced temperature due to severe lattice distortion. The obtained maximum of magnetic entropy change for a field change of 5 T is about 12.8 J kg −1 K −1 near room temperature, and increases with more doping carbon content to about 22.4 J kg −1 K −1 in MnAsC 0.03 and 13.2 J kg −1K −1 in MnAsC 0.05.

Magnetic and magnetocaloric results of magnetic field-induced transitions in La 1−xCe xMn 2Si 2 ( x=0.35 and 0.45) compounds

The La 1− x Ce x Mn 2Si 2 compounds ( x=0.35 and 0.45) exhibit an antiferromagnetic–ferromagnetic transition caused by the changes in distance between Mn atoms due to temperature changes. A field-induced transition from antiferromagnetic state to ferromagnetic state at a critical field, which decreases with increase in temperature, can also be induced by applying a magnetic field. In this paper our aim is to study the magnetization and magnetocaloric effect, close to transition temperatures. Our subsidiary aim is to examine the temperature dependence of critical field and ferromagnetic fraction of compounds. The variation of magnetocaloric effect with temperature is correlated with the ferromagnetic–antiferromagnetic phase coexistence. Our final aim is to examine the harmony between magnetocaloric effect values calculated both by the Maxwell theory and by the Landau theory.

Spontaneous and Field-Induced Magnetic Phase Transitions in Tb&lt;sub&gt;1-x&lt;/sub&gt;R&lt;sub&gt;x&lt;/sub&gt;Mn&lt;sub&gt;6&lt;/sub&gt;Sn&lt;sub&gt;6&lt;/sub&gt; (R = Gd, Y) Compounds

Magnetization curves and magnetic susceptibility of Tb1 xRxMn6Sn6 (R = Gd, Y) compounds have been measured for aligned powder samples. Concentration dependences of the spin-reorientation transition temperature and temperature dependences of critical fields of the field-induced magnetic transitions have been determined. For the compound Tb0.1Y0.9Mn6Sn6 with the spiral magnetic structure, we found that application of hydrostatic pressure facilitates the ferrimagnetic ordering. This unusual feature is supported by the observation of a large negative spontaneous volume magnetostriction for TbMn6Sn6. The obtained results are discussed in a model considering three different interlayer Mn-Mn exchange interactions in these compounds.