Levitation Force Investigation of Bulk HTSC Above Halbach PMG with Different Cross-Section Physical Dimensions by 3D-Modeling Numerical Method

The levitation force of a bulk high temperature superconductor (HTSC) over Halbach permanent magnet guideways (PMG) with different cross-section configuration is studied by numerical method. The Halbach PMG is composed of three host permanent magnets (HPMs) and two slave permanent magnets (SPMs). One cylindrical bulk HTSC with a diameter of 30 mm and height of 15 mm is used. The 3D-modeling is formulated by the H-method. The numerical resolving codes are practiced using finite element method (FEM). The E-J power law is used to describe the electric current nonlinear characteristics of bulk HTSC. By the method, the influence of the cross-section physical dimensions of Halbach PMG on the levitation forces of bulk HTSC levitated above the PMG is studied. The simulation results show that increasing the width of SPM ( \(W_\mathrm{SPM})\) can enhance the bulk HTSC levitation performance immediately under the condition of keeping the ratio of \(W_\mathrm{HPM}\) ( \(W_\mathrm{HPM}\) : the width of HPM) to \(W_\mathrm{SPM}\) between 1.6 and 1.8, the ratio of td (the height of the PMG) to \(W_\mathrm{HPM }\) between 1.2 and 1.4. By the method, the bulk HTSC better levitation performance can be expected.     

Effects of Initial Cooling Conditions and Measurement Heights on the Levitation Performance of Bulk MgB_{2} Superconductor at Different Measurement Temperatures

The levitation properties of MgB \(_{2}\) prepared by hot press at 200  \(^{\circ }\) C and then pellet/closed tube method has been investigated. The vertical and lateral levitation forces ( \(F_{z}\) and \(F_{x})\) on a cylindrical NdFeB permanent magnet (PM) below a disk-shaped bulk MgB \(_{2}\) were measured during the vertical and lateral traverses of the PM in different cooling heights (CHs) and measurement heights (MHs) at temperatures of 20, 25 and 30 K to investigate the effect of the initial CH and MH on the levitation performance of MgB \(_{2}\) . For temperatures below 30 K, it was observed that \(F_{z}\) increases with increasing CH. However, a minute variation in \(F_{z}\) and a big hysteresis loop are observed at 30 K. From the lateral traverses, it was obtained that the \(F_{z}\) with attractive character increases with decreasing MH and the hysteresis effect increases for small MHs due to the increment of the magnetic field intensity which the sample feels with decreasing MH. In addition, it was seen that the character of \(F_{x}\) varies depending on both MH and measurement temperature. The higher hysteresis obtained in \(F_{x}\) than in \(F_{z}\) during lateral traverses implies that the motion of the flux lines in MgB \(_{2}\) is especially in lateral rather than vertical direction. Finally in this study, it was shown that the levitation performance of MgB \(_{2}\) depends not only on the measurement temperature but also on the CH and MH conditions. These results can be useful for optimizing the levitation performance of MgB \(_{2}\) superconductors for potential applications.     

Investigation of Magnetic Memory Signals Induced by Dynamic Bending Load in Fatigue Crack Propagation Process of Structural Steel

Metal magnetic memory effect, induced by applied stress under the excitation of the geomagnetic field, has attracted a lot of attentions due to its unique advantages of stress concentration identification and early damage detection for ferromagnetic materials. To further investigate the regularity of magnetic memory signals in the fatigue crack propagation process under the dynamic bending load, the surface magnetic field intensity \(H_{p}(y)\) of ferromagnetic structural steel was measured throughout the dynamic three-point bending fatigue tests; variation of \(H_{p}(y)\) and its maximum gradient \(K_{max}\) were studied; meanwhile the possibility of using \(K_{max}\) to predict the fatigue crack propagation was discussed. The results showed that \(H_{p}(y)\) was relatively stable at different loading cycles and its maximum value appeared at the fatigue crack area before the specimen fractured; instead the \(K_{max}\) increased exponentially with the increase of loading cycles, and an approximate linear relationship was found between \(K_{max}\) and crack length 2a. The cause for this phenomenon was also discussed.     

Multi-vortex State Induced by Proximity Effects in a Small Superconducting Square

The influence of the different negative values of the deGennes parameter \(b\) in the thermodynamic properties of a superconducting infinitely long prism of square cross section area \(S=9\xi ^{2}(0)\) in the presence of a magnetic field is investigated theoretically by solving numerically the nonlinear Ginzburg-Landau equations; \(\xi (0)\) is the coherent length at zero temperature. We obtain the vorticity, magnetic induction, Cooper pair density, magnetization and phase of the order parameter as functions of the external applied magnetic field and the \(b\) parameter. Our results show that a multi-vortex state appear in the sample choosing a convenient value of \(b<0\) parameter, even for such small system. Also, we study a superconducting parallelepiped of volume \(V=Sd\) by means of true \(3D\) numerical simulations; \(d\) is the height of the parallelepiped. We focused our analysis on the way which the magnetization curves approximate from \(d\) finite to the characteristic curve of \(d\rightarrow \infty \) . This is the case for which the magnetic field and the order parameter are invariant along \(z\) -direction. For a superconductor of size \(S=9\xi ^2(0)\) we find that the limit below which the system should be considered a real three-dimensional sample when is \(d=8\xi \) .     

Study of Dynamic Magnetism in Low Bandwidth Manganite Pr_{1-x}Ca_xMnO_3 (x = 0.3 - 0.5) by Ac Susceptibility Measurements

The complex ac susceptibility is studied in the low bandwidth manganite Pr $_{1-x}$ Ca $_x$ MnO $_3$ at doping range $x = 0.3 - 0.5$ with and without a superimposed background dc field. It is found that all the samples had a frustrated magnetic phase. The fraction of the frustrated magnetic phase in the samples diminished as the Ca concentration was increased. The suppression of the frustrated magnetic phase is explained by the formation of charge order (CO) phase around 250 K in the samples with $x =$ 0.4 and 0.5. This result indicates that formation of CO-antiferromagnetic states reduces the magnetic frustration in the system and the spin glass behaviour is mainly associated with the coexisting antiferromagnetic—ferromagnetic phase in low bandwidth manganites.     

The Magnetically-Tuned Transition-Edge Sensor

We present the first measurements on the proposed magnetically-tuned superconducting transition-edge sensor and compare the modified resistive transition with the theoretical prediction (Sadleir et al., IEEE Trans App Supercond 23:2101405, 2013). A TES’s resistive transition is customarily characterized in terms of the unitless device parameters \(\alpha \) and \(\beta \) corresponding to the resistive response to changes in temperature and current respectively. We present a new relationship between measured IV quantities (sensor current \(I\) and voltage \(V\) ) and the parameters \(\alpha \) and \(\beta \) and use these relations to confirm we have stably biased a TES with negative \(\beta \) parameter with magnetic tuning. Motivated by access to this new unexplored parameter space, we investigate the conditions for bias stability of a TES taking into account both self and externally applied magnetic fields.     

Evaluation of Power Heat Losses in Multidomain Iron Particles Under the Influence of AC Magnetic Field in RF Range

The magnetic properties and hyperthermia effect were studied in a magnetorheological fluid (MRF) containing iron particles of $1 \upmu \mathrm{m}\, \text{ to}\, 5 \,\upmu \mathrm{m}$ in diameter. The measurements showed that the magnetization in the saturation state reaches a value of 171 $\text{ A}\cdot \text{ m}^{2}\cdot \mathrm{kg}^{-1}$ with very small values of coercivity and remanence. They also showed the ferromagnetic behavior in the system together with a value of the magnetic susceptibility of 1.7. Theoretical and experimental results of the calorimetric effect investigation under a changeable magnetic field of high frequency ( $f = 504$ kHz) in an MRF will be presented in the article. The sample was subjected to an alternating magnetic field of different strengths ( $H = 0$ to 4 $\text{ kA}\cdot \text{ m}^{-1})$ . It results from a theoretical analysis that the heat power density (released in the MRF sample) referenced to the eddy current is proportional to the square of frequency, the magnetic field amplitude, and the iron grain diameter. Experimental results indicate that there are some reasons for the released heat energy such as: energy losses from magnetic hysteresis and eddy currents induced in the iron grains. If the magnetic field intensity amplitude grows, the participation of losses connected with magnetic hysteresis is increased. From the calorimetric measurements, the conclusion is as follows: for a magnetic field $H<1946\,\text{ A}\cdot \mathrm{m}^{-1}$ , the eddy current processes dominate in the heat generation mechanism, whereas hysteresis processes for the total release of thermal energy dominate for higher magnetic fields. Both mechanisms take equal parts in heating the tested sample at a magnetic field intensity amplitude $H= 1946\,\text{ A}\cdot \mathrm{m}^{-1}$ . The specific absorption rate referenced to the mass unit of the MRF sample at the amplitude of the magnetic field strength 4 $\text{ kA}\cdot \mathrm{m}^{-1}$ equals 24.94 $\text{ W} \cdot \mathrm{kg}^{-1}$ at a frequency $f$ = 504 kHz.     

Electronic Structure and Thermodynamic Properties of the Cubic Antiperovskite Compound InNCe_{3} via First-Principles Calculations

Elastic, thermodynamic, electronic, and magnetic properties in the cubic antiperovskite InNCe $_{3}$ 3 compound are derived from the full-potential linear muffin-tin orbital method. From the computed elastic constants, theoretical values of Young’s modulus, the shear modulus, Poisson’s ratio, Lamé’s coefficients, sound velocities, and the Debye temperature are evaluated. Analysis of the ratio between the bulk modulus and the shear modulus shows that InNCe $_{3}$ 3 is brittle in nature. The variations of elastic constants with pressure indicate that this compound possesses higher mechanical stability in the pressure range from 0 to 40 GPa. The electronic and magnetic properties of this compound are calculated by adding the Coulomb interaction $U$ U to improve the results.     

Influence of Magnetic Field and LO Phonon Effects on the Spin Polarization State Energy of Strong-Coupling Bipolaron in a Quantum Dot

On the basis of Lee–Low–Pines unitary transformation, the influence of magnetic field and LO phonon effects on the energy of spin polarization states of strong-coupling bipolarons in a quantum dot (QD) is studied by using the variational method of Pekar type. The variations of the ground state energy $E_0$ and the first excited state the energy $E_1$ of bipolarons in a two-dimensional QD with the confinement strength of QDs $\omega _0$ , dielectric constant ratio $\eta $ , electron–phonon coupling strength $\alpha $ and cyclotron resonance frequency of the magnetic field $\omega _{c}$ are derived when the influence of the spin and external magnetic field is taken into account. The results show that both energies of the ground and first excited states ( $E_0$ and $E_1)$ consist of four parts: the single-particle energy of electrons $E_\mathrm{e}$ , Coulomb interaction energy between two electrons $E_\mathrm{c}$ , interaction energy between the electron spin and magnetic field $E_\mathrm{S}$ and interaction energy between the electron and phonon $E_{\mathrm{e-ph}}$ ; the energy level of the first excited state $E_1$ splits into two lines as $E_1^{(1+1)}$ and $E_1^{(1-1)}$ due to the interaction between the single-particle “orbital” motion and magnetic field, and each energy level of the ground and first excited states splits into three “fine structures” caused by the interaction between the electron spin and magnetic field; the value of $E_{\mathrm{e-ph}}$ is always less than zero and its absolute value increases with increasing $\omega _0$ , $\alpha $ and $\omega _c$ ; the effect of the interaction between the electron and phonon is favorable to forming the binding bipolaron, but the existence of the confinement potential and Coulomb repulsive energy between electrons goes against that; the bipolaron with energy $E_1^{(1-1)}$ is easier and more stable in the binding state than that with $E_1^{(1+1)}$ .     

Microkelvin Thermometry with Bose–Einstein Condensates of Magnons and Applications to Studies of the AB Interface in Superfluid ^3He

Coherent precession of trapped Bose–Einstein condensates of magnons is a sensitive probe for magnetic relaxation processes in superfluid $^3$ He-B down to the lowest achievable temperatures. We use the dependence of the relaxation rate on the density of thermal quasiparticles to implement thermometry in $^3$ He-B at temperatures below $300\,\upmu $ K. Unlike popular vibrating wire or quartz tuning fork based thermometers, magnon condensates allow for contactless temperature measurement and make possible an independent in situ determination of the residual zero-temperature relaxation provided by the radiation damping. We use this magnon-condensate-based thermometry to study the thermal impedance of the interface between A and B phases of superfluid $^3$ He. The magnon condensate is also a sensitive probe of the orbital order-parameter texture. This has allowed us to observe for the first time the non-thermal signature of the annihilation of two AB interfaces.     

Magnetocaloric Effect in Half-Metallic Double Perovskite Sr_{0.4}Ba_{1.6-x}Sr_{x}FeMoO_{6}

The magnetocaloric effect in half-metallic double perovskite Sr $_{0.4}$ Ba $_{1.6-x}$ Sr $_{x}$ FeMoO $_{6}$ (x = 0, 0.2, 0.4, 0.6) was investigated. It is shown that Sr $_{0.4}$ Ba $_{1.6-x}$ Sr $_{x}$ FeMoO $_{6}$ exhibits a magnetic entropy change of 0.078 J $\,\cdot \, $ kg $^{-1}\,\cdot \, $ K $^{-1}$ upon 0.2 T magnetic field variation. Through these results, polycrystalline samples of Sr $_{0.4}$ Ba $_{1.6-x}$ Sr $_{x}$ FeMoO $_{6 }$ have some potential applications for magnetic refrigerants over a wide-temperature range, including room temperature.     

Containerless Measurements of Density and Viscosity for a Cu_{48}Zr_{52} Liquid

The densities of solid and liquid Cu \(_{48}\) Zr \(_{52}\) and the viscosity of the liquid were measured in a containerless electrostatic levitation system using optical techniques. The measured density of the liquid at the liquidus temperature (1223 K) is (7.02 \(\pm \) 0.01) g \(\cdot \) cm \(^{-3}\) and the density of the solid extrapolated to that temperature is (7.15 \(\pm \) 0.01) g \(\cdot \) cm \(^{-3}\) . The thermal expansion coefficients measured at 1223 K are (6.4 \(\pm \) 0.1) \(\,\times \,10^{-5}\) K \(^{-1}\) in the liquid phase and (3.5 \(\pm \) 0.3) \(\,\times \,10^{-5}\) K \(^{-1}\) in the solid phase. The viscosity of the liquid, measured with the oscillating drop technique, is of the form \(A\exp \left[ \left( {{E}_{0}}+{{E}_{1}}\left( 1/T-1/{{T}_{0}} \right) \right) \times \left( 1/T-1/{{T}_{0}} \right) \right] \) , where \({{T}_{0}}=1223\) K, \(A= (0.0254 \pm 0.0004)\) Pa \(\cdot \) s, \({{E}_{0}}\) =  (8.43 \(\pm \) 0.26) \(\,\times \,10^3\) K and \({{E}_{1}}\) =  (1.7 \(\pm \) 0.2) \(\,\times 10^7\) K \(^{2}\) .     

Stimulated acoustic emissions from coupled strings

We consider traveling transverse waves on two identical uniform taut strings that are elastically coupled through springs that gradually decrease their stiffness over a region of finite length. The wave system can be decomposed into two modes: an in-phase mode ( $+$ ) that is transparent to the coupling springs, and an out-of-phase mode ( $-$ ) that engages the coupling springs and can resonate at a particular location depending on the excitation frequency. The system exhibits linear mode conversion whereby an incoming ( $+$ ) wave is reflected back from the resonance location both as a propagating ( $+$ ) wave and an evanescent ( $-$ ) wave, while both types emerge as propagating forward through the resonance location. We match a local transition layer expansion to the WKB expansion to obtain estimates of the reflection and transmission coefficients. The reflected waves may be an analog for stimulated emissions from the ear.     

Damping properties of epoxy-based composite embedded with sol–gel-derived Pb(Zr 0.53 Ti 0.47 )O 3 thin film with different thicknesses

Pb(Zr $_{\mathbf{0\boldsymbol{\cdot}53}}$ Ti $_{\mathbf{0\boldsymbol{\cdot}47}})$ O ₃ (PZT) thin films were prepared on Pt/Ti/SiO ₂ /Si substrate by sol?Cgel method. The effect of film thickness on microstructure, ferroelectric and dielectric properties was investigated. The single-phase PZT films were obtained with different thicknesses. PZT films with a thickness of 190?C440?nm had better dielectric and ferroelectric properties. The epoxy/PZT film/epoxy sandwiched composites were prepared. The thickness of PZT films influenced their damping properties of the composites, and the epoxy-based composites embedded with 310?nm-thick PZT films had the largest damping loss factor of 0 $\boldsymbol{\cdot} $ 915.     

Interaction of Helium Rydberg State Atoms with Superfluid Helium

The pair potentials between ground state helium and Rydberg He $^*(2s,2p,3s)$ atoms are calculated by the full configuration interaction electronic structure method for both the electronic singlet and the triplet manifolds. The obtained pair potentials are validated against existing experimental molecular and atomic data. Most states show remarkable energy barriers at long distances ( $R > 5$ Å), which can effectively stabilize He $^*$ against the formation of He $_2^*$ at low nuclear kinetic energies. Bosonic density functional theory calculations, based on the calculated pair potential data, indicate that the triplet ground state He $^*$ reside in spherical bubbles in superfluid helium with a barycenter radius of 6.1 Å at the liquid saturated vapor pressure. The pressure dependency of the relative He $^*$ $2s$ $^3S$ $\rightarrow $ $2p$ $^3P$ absorption line blue shift in the liquid was obtained through both the statistical line broadening theory as well as the dynamic adiabatic following method. The pronounced difference between the results from the static and dynamic models is attributed to the dynamic Jahn–Teller effect that takes places in the electronically excited state within the dephasing time of 150 fs. Transient non-thermalized liquid surroundings near He $^*$ may contribute to an artificial reduction in the absorption line blue shift by up to 30 cm $^{-1}$ .     

Crystal growth and magnetic property of YFeO 3 crystal

YFeO $_{\boldsymbol 3}$ and other rare earth substituted crystals with distorted orthorhombic pervoskite-like structure (space group, Pbnm) have attracted much attention due to their remarkable magnetic properties of primary significance for technological applications. In the present work, the floating zone growth of YFeO $_{\boldsymbol 3}$ crystals has been systematically investigated and high quality YFeO $_{\boldsymbol 3}$ crystal was obtained by optimized process. The magnetic properties of YFeO $_{\boldsymbol 3}$ crystal were investigated, and it indicated the high magneto-optical property in YFeO $_{\boldsymbol 3}$ crystals with specific orientation due to its anisotropy. YFeO $_{\boldsymbol 3}$ crystals display superior performance in the application magneto-optical current sensors and fast latching optical switches.     

Thermodynamics of the Spin-1/2 Two-Leg Ladder Compound (C_5H_{12}N)_2CuBr_4

The thermodynamic behavior of the spin \(S=1/2\) antiferromagnetic two-leg ladder compound (C \(_5\) H \(_{12}\) N) \(_{2}\) CuBr \(_{4}\) in a uniform magnetic field is studied using numerical and analytical approaches. The entropy \(S(H,T)\) and specific heat \(C(H,T)\) are calculated. The specific heat shows various behaviors in different regions of the magnetic field. The field dependence of the specific heat is almost symmetric about the average of quantum critical fields in complete agreement with experimental results. In addition, it is found that during an adiabatic demagnetization process, temperature drops in the vicinity of the field induced zero-temperature quantum phase transitions.     

Quartz Tuning Forks as Cryogenic Vacuum Gauges

We report measurements of the mechanical \(Q\) of a 32.7 kHz quartz tuning fork as a function of pressure for helium and argon at T  \(=\)  300 K and for helium in the temperature range 7.0–0.7 K. In the low pressure ballistic regime, the damping due to the surrounding gas is inversely proportional to \(P\) , while for higher pressures, a hydrodynamic treatment accounts for most of the variation of \(Q\) with \(P\) . We have combined the ballistic and hydrodynamic models together with calculations of the thermal transpiration correction to correlate the tuning fork \(Q\) at low temperature with the pressure measured with a room temperature pressure gauge. The fork was found to be useful as an in situ pressure gauge for pressures above \(\sim \) 0.1 mTorr. A dissipation peak and frequency drop associated with the superfluid transition in the adsorbed helium film is also observed for \(T<1.4\)  K.     

The Improved Superconducting Properties in the Ex-situ Sintered MgB_{2} Bulks with Mg Addition

The ex-situ method to prepare MgB \(_{2}\) superconductors is favorable in terms of bulk density compared to the in-situ method. Since the packing factor of ex-situ MgB \(_{2}\) is higher than that of in-situ MgB \(_{2}\) , a better \(J_{c}\) , even higher than that of in-situ, is naturally expected if strong grain connectivity is achieved. In the present work, ex-situ MgB \(_{2 }\) polycrystalline bulks with Mg addition were prepared by sintering. Combined with phase composition analysis, microstructure observation and superconducting properties measurement, it is found that Mg addition can obviously reduce MgO impurities, accelerate the self-sintering of MgB \(_{2}\) and even promote the formation of sintering necks between MgB \(_{2}\) grains. Consequently, the sintering density and grain connectivity is enhanced, and the \(J_{c}\) is improved across the whole magnetic field in the ex-situ MgB \(_{2}\) sample with Mg addition. Mg addition is a promising and effective way to further enhance \(J_{c}\) of ex-situ MgB \(_{2}\) superconductors.