Ac Field Amplitude Research Articles

Magnetic properties of Sm-doped Bi-2223 superconductor studied by low field local Hall generator ac susceptibility

We studied the grain boundary properties of Sm doped Bi(Pb)SrCaCuO using the Hall generator ac susceptibility ( χ = χ′ + iχ″). Hall generator is a convenient tool to investigate the shielding effect of superconductors under extremely low magnetic fields. Using a Hall generator system, we have investigated diamagnetic shielding behavior of Bi 1.6Pb 0.4Sr 2Ca 2− x Sm x Cu 3O y samples with x = 0.0, 0.0005, 0.001, 0.005, 0.01 and 0.1. The susceptibility measurements were carried out for ac field amplitudes of 47, 94, 141, 188 and 235 A/m with the frequency of 20 Hz. The critical temperatures were estimated from the temperature dependence of the ac susceptibility curves. We have also employed X-ray diffraction, energy dispersive X-ray fluorescent and scanning electron microscopy techniques to investigate the effect of Sm doping.

Magnetic instabilities along the superconducting phase boundary of Nb∕Ni multilayers

We report vibrating reed and superconducting quantum interference device magnetometer data that exhibit prominent dips or oscillations of the superconducting (SC) onset temperature, ΔTC(H)≈0.01–0.7K, for a [Nb(23nm)∕Ni(5nm)]5 multilayer (ML) in dc magnetic fields applied nearly parallel to the ML plane. The vibrating reed data exhibit reproducible structures below TC that may reflect multiple SC transitions, but they are sensitive to ac field amplitude and dc field orientation. This striking behavior poses challenges for theoretical and experimental investigations of interfaces between SC and ferromagnetic layers that involve magnetic pair breaking effects, “pi phase shifts” of the SC order parameter, and exotic (“LOFF”) pairing states. Alternatively, the anomalies may mark dynamical instabilities within a confined, strongly anisotropic Abrikosov vortex lattice.

Ac susceptibility of bicrystal-like type-II superconducting films

The ac susceptibility of a type-II superconducting thin film divided into two halves by a narrow mid region with a smaller value of critical-current density is calculated by a model based on Bean’s critical-state model and energy minimization. Results are compared to measurements of ac susceptibility as a function of ac-field amplitude of artificial bicrystal-like films prepared by photolithography patterning a gridline of holes on epitaxial YBCO thin films. A qualitative agreement is found between calculated and experimental results.

Effect of the amplitude of the AC magnetic field on the vortex dynamics: A quantitative analysis in Nb and NbTi polycrystalline samples

The harmonics of the AC magnetic susceptibility as a function of the temperature have been measured on Nb and NbTi polycrystalline samples, at various amplitudes of the AC magnetic field, without a DC field. The data have been analysed in terms of Cole–Cole plots, i.e. the imaginary part as a function of the real part. A similar AC field dependence in the height of the maximum of the first harmonics Cole–Cole plots has been observed for both materials. The experimental results have been compared with numerical curves obtained by integrating the nonlinear diffusion equation for the magnetic field inside the sample with different flux creep models. It has been proved that the AC field amplitude dependence have to be included in the existing models in order to reproduce the behaviour of the experimental data. Finally, a quantitative agreement has been achieved by supposing different vortex dynamical regimes tuned by changing of the AC field amplitude.

The effect of ac magnetic fields on the lifting power of levitating superconductors

This study deals with the decrease in the levitation force under the action of an ac fieldup to the frequency at which oscillations of the superconducting suspension arelimited by inertia. The lifting force was measured as a function of the ac fieldamplitude and the exposure time. It was shown that the force quickly decreased atthe moment the ac field was applied and then continued diminishing, but at alower rate. A qualitative model was proposed, taking into account two effects ofthe ac field on the magnetization of the levitating superconductor: a completedestruction of the critical state in some section of the superconductor (to a depthλac) and the initiation of a faster magnetic relaxation in the region where the inductiongradient is preserved.

Low field AC-susceptibility study on γ -irradiated Bi1.2Pb0.33Sr1.54Ca2.06Cu3O10+δ superconductor

We report here, the effect of γ-irradiation on low field AC susceptibility as a function of temperature on the grown polycrystalline Bi1.2Pb0.33Sr1.54Ca2.06Cu3O10+δ sample. The sample was irradiated with γ-ray dose of 100 MR and 300 MR. The temperature dependent AC susceptibility measurements have been carried out with varying AC field amplitude H ac (0.5 to 9.0 Oe) at frequency 131.1 Hz on both un-irradiated and irradiated samples. AC susceptibility measurements as a function of temperature at AC field amplitude H ac = 2.0 Oe have also been carried out with varying frequency (31.1 Hz to 1131.1 Hz). The temperature dependence of AC susceptibility with varying amplitude has been analyzed using well defined Bean's critical state model. The critical current density (J c) is calculated as a function of both AC field amplitude (H ac) and temperature. An increase in J c with the increase of γ-dose has been found.

Investigation of Sm → Ca substitution in Bi(Pb)SrCaCuO high temperature superconductor by low field AC magnetic susceptibility

We have investigated the effect of Sm substitution in Bi(Pb)SrCaCuO system by performing AC susceptibility ( \(\chi = \chi ' + i\chi ''\)), XRD (X Ray Diffraction) and SEM (Scanning Electron Microscopy) measurements. The Sm → Ca substitution (Bi1.6Pb0.4Sr2Ca2−xSmxCu3Oy) was carried out by conventional solid-state reaction method. The susceptibility measurements were carried out at different values of the AC field amplitudes. The imaginary part of susceptibility is used to estimate the intergranular critical current density by means of the Bean’s model. The intergranular critical current density (Jc) of pure sample is found to be about 68 A/cm2 at 95 K. The intergranular Jc is seen to decrease with increasing Sm substitution. XRD pattern and SEM micrographs are given to provide information about Bi-2223 phase and grain size respectively.

Analysis of Complex Transverse Susceptibility Method for Determination of Volume and Anisotropy Field Distributions in Recording Media

This paper is dedicated to the analysis of determination of volume and anisotropy field distributions using the complex transverse susceptibility (TS). We consider in our study two-dimensional arrays of particles as magnetic patterned media. It is shown that the amplitude of excitatory ac field and the interactions between particles play an important role

Magnetic history dependence of the AC susceptibility of GdSr2RuCu2Oz

AbstractThe AC susceptibility of GdSr2RuCu2Oz samples has been measured as function of the temperature, at different AC field amplitudes (from 1 to 16 G) and frequencies (in the range [10‐103 Hz]), applied parallel to the major axis of the sample, and without any additional DC magnetic field. In particular we have analysed the temperature region above the Superconducting critical temperature Tc, and around the magnetic transition temperature Tm. Our attention has been focused on the differences between the curves measured after cooling the sample in zero AC field (Zero AC Field Cooling or ZAFC) and those measured after cooling in presence of a non zero AC field (AC Field Cooling or AFC). Clear differences between the ZAFC and AFC susceptibility curves appear in the temperature range between Tc and Tm, and they depend on the measuring field amplitude and frequency. Finally, indications of a spin glass behaviour in Ru‐1212 system observed from its AC magnetic response are reported (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Linear and Nonlinear Electric Susceptibility in the Quantum Domain State of SrTi18O3

The complex dielectric susceptibility of SrTi18O3 has been measured at frequencies 10−3 ≤ f ≤ 105 Hz and temperatures 5 ≤ T ≤ 30 K with ac field amplitudes 0.01 ≤ E 0 ≤ 10 kV/m in order to inspect different mechanisms of the polarization reversal. This system displays a very strong nonlinear effect in its quantum domain (“ferroelectric”) state as evidenced by the field dependence of the susceptibility. Depending on the amplitude of the probing field partial or almost complete polarization reversal can be achieved at moderate values of E 0 being available in standard dielectric spectrometers.

Ac magnetic susceptibility of the self-doped manganites La 0.9− xSr 0.1MnO 3 ( x = 0.02 and 0.03)

The real ( χ′) and imaginary ( χ″) components of the ac susceptibility of the self-doped manganites La 0.9− x Sr 0.1MnO 3 ( x = 0.02 and 0.03), have been studied as functions of temperature, ac field amplitude and frequency. Both χ′ and χ″ of the samples are dependent on the ac magnetic field parameters. The influence of magnetic field amplitude and frequency on the ac susceptibility increases by increasing La-vacancy. Increasing La-vacancy, the inhomogeneity of sample increases more, resulting in the formation of strong domain wall pinning centers. The observation of low temperature anomaly and amplitude and frequency dependence of ac susceptibility in the ferromagnetic region is determined mainly by the domain wall dynamics, rather than due to the glassy spin configuration or spin frustration. Activation energy, extracted from Arrhenius-like expression for the frequency and temperature in the experimental ranges could be presented with the following equation: U ( H , T ) = U 0 1 − T / T 0 H − 0.45 .

On the correlation between order parameter, superconducting volume fraction and critical current density in R: 123 superconductors

Resistivity and low field ac susceptibility measurements are made on R: 123 superconducting samples with different rare earth elements R. The order parameter dimensionality OPD is deduced from resistivity versus temperature plot using the Aslamazov and Larkin expression, while the analysis of the temperature dependence of ac susceptibility is done employing Beans’ critical state model and with the help of the Ravi expression. With increasing R, the critical temperatures T c are nearly kept constant (∼90 K), while the crossover temperatures T o are shifted to lower values. Moreover, the superconducting order parameter OPD is shifted toward 2D behavior. On the other hand, the values of superconducting volume fraction f g decrease with increasing ac field amplitude H m for all samples and it is higher in Er: 123 sample than in Nd: 123 sample. Although the values of critical current density J c at the peak temperature T m are nearly unchanged with increasing R, the values of J c ( T ) , at T < T m and T > T m , are found to be dependent on the chosen R. The correlation between the above calculated parameters against R is also mentioned.

Influence of the dc and ac field intensity on electric permittivities of (Na0.5Bi0.5)0.88Ba0.12TiO3 ceramics

The electric permittivity measurements under different ac or dc field amplitudes on lead-free (Na0.5Bi0.5)0.88Ba0.12TiO3 ceramics were performed. A significant increase or decrease in permittivities was observed with increasing ac or dc fields intensity, respectively. It was found that temperature T m decreases or increases with increasing ac or dc fields, respectively. When ac field amplitude increased, stronger frequency relaxation around T m and greater shift in T m was observed. This was in opposite to the effect of dc field intensity. The obtained results were discussed in terms of polar region behaviour in external electric fields.

Ac loss properties of YBCO superconducting tapes fabricated by IBAD-PLD technique

Temperature dependence of the ac loss in YBCO superconducting tapes fabricated by IBAD-PLD technique was investigated. The ac loss was measured with a saddle-shaped pickup coil by applying magnetic field perpendicular to the tape. Temperature dependence of Ic-B characteristics was estimated from the observed magnetization curves. The Ic-B curves normalized by the zero-field Ic at the respective temperature coincided with one master curve regardless of temperature. Ic-B characteristics of YBCO superconducting tapes are scaled with temperature. According, when the magnetization curves and the ac loss vs field amplitude curves are normalized by using the zero field Ic at the respective temperature, they coincided with one master curve for any temperature from 4.2 to 77 K. It is verified that the magnetization and the ac loss are scaled with temperature.

Linear and nonlinear AC susceptibility studies in La(Mn 1−xCu x)O 3

The linear and nonlinear AC susceptibility as a function of temperature were measured on LaMn 1− x Cu x O 3 compounds for x = 0.05 – 0.30 . Samples with x ⩾ 0.10 exhibit paramagnetic to ferromagnetic transitions followed by low temperature spin glass like transition. The linear susceptibility exhibits strong frequency dependence and is analyzed in terms of standard theoretical model for spin glass. The magnitude and peak temperature of nonlinear susceptibility vary with AC field amplitudes. They are analyzed in terms of critical behaviour in the vicinity of spin glass transition temperature and the critical exponent is found to be 3.2.

AC susceptibility and intergranular critical current density study in pure and Ag doped (La 1− xY x) 2Ba 2CaCu 5O z superconductors

The temperature and AC field amplitude variations of AC susceptibility have been measured on pure and 5 wt% Ag doped (La 1− x Y x ) 2Ba 2CaCu 5O z superconductors. The AC susceptibility as a function of field have been analyzed using Kim's critical state model. The temperature dependence of intergranular critical current density and the effective volume fractions of the grains have been estimated. The Ag doped samples show relatively large critical current density due to the improved intergranular coupling. The exponent of temperature variation of critical current density suggests that the weak links form superconductor–normal metal–superconductor (SNS) type of junctions for all the samples.

Effects of geometric anisotropy on higher harmonic response of hard type-II superconductors

Fundamental and higher harmonic responses of hard type-II materials are studied for a cylindrical geometry of any arbitrary cross-section subjected to an AC magnetic field B= B AC cos (ω t) along any general direction. The parallel and two perpendicular in-phase (χ′) and out-of-phase (χ”) AC susceptibility components are analytically calculated and their variations with respect to the change in the applied field orientations and AC field amplitude are studied. The effect of geometrical anisotropy on the fundamental and higher harmonic AC response of the sample is studied by varying aspect ratio of a rectangular cylinder for various values of the AC field amplitude.

Temperature scaling of ac loss in YBCO superconducting tapes fabricated by theIBAD-PLD technique

Temperature dependence of the ac loss in YBCO superconducting tapesfabricated by the IBAD-PLD technique was investigated. The ac loss wasmeasured with a saddle-shaped pickup coil by applying a magnetic fieldperpendicular to the wide surface. Temperature dependence of the critical current,Ic, versus themagnetic field, B, characteristics was estimated from the magnetization curves observed. By definingBb(T) as a specific valueof B at the breakingpoint of the Ic–B curve in logarithmic scale at the respective temperature,T,Ic for0≤B<Bb was nearly constantindependent of B, and Ic forB>Bb decreased inproportion to the (1−γ)th power of B, where γ is a pin parameter of the Irie–Yamafuji model and0<γ<1. In addition, the temperature dependencies ofBb and zero fieldIc were almostidentical and γ had no temperature dependence. We found that the normalizedIc–B curves by the zerofield Ic at the respectivetemperature, Ic0(T), coincide with one master curve regardless of temperature. This means that theIc–B characteristics of YBCO superconducting tapes are scaled with temperature. Consequentlyit was clarified that the magnetization and the ac loss are scaled with temperature. Themagnetization curves and the ac loss versus field amplitude curves, which are normalized by usingIc 0(T), coincided with one master curve for any temperature from 4.2 to 77 K. This fact is veryuseful in the design of YBCO superconducting systems because it is possible to estimatethe ac loss at any temperature only if we know the field amplitude dependence of the acloss at some temperature, e.g., 77 K, and the temperature dependence of zero fieldIc.

Effect of dc bias field superimposed with ac field amplitudes on the hysteresis loss in a sintered YBCO superconductor

We have investigated the magnetic behaviour of a sintered YBCO sample by ac susceptibility measurements in the presence of a static bias dc magnetic field. Calculations of the imaginary part of the ac susceptibility or hysteresis losses have been performed to account for the measured ac loss valley. Our calculations based on the critical state model with j c = α( T)/ B n reproduce the experimental data quite well. We also explored the effect of temperature exponent in the pinning strength parameter on the ac loss valley behaviour.

Micromagnetic Simulation of the imaginary part of the transverse susceptibility

A micromagnetic model based on magnetization vector dynamics described by the stochastic Landau-Lifshitz-Gilbert (SLLG) equation for the transverse susceptibility (TS) of particulate media is presented. The effect of the amplitude of excitatory ac field and the effect of thermal relaxation is taken into account.