Films In Magnetic Field Research Articles

Peak effect at microwave frequencies in swift heavy ion irradiated YBa2Cu3O7-δ thin films

The vortex dynamics at microwave frequencies in YBa2Cu3O7-δ (YBCO) films have been studied. We observe a peak in the microwave (4.88 and 9.55 GHz) surface resistance in some films in magnetic fields up to 0.8 T. This is associated with the ‘peak-effect’ phenomenon and reflects the order-disorder transformation of the flux line lattice near the transition temperature. Introduction of artificial pinning centers like columnar defects created as a result of irradiation with 200 MeV Ag ion (at a fluence of 4×1010 ions/cm2) leads to the suppression of the peak in films previously exhibiting ‘peak effect’.

Peak effect in surface resistance at microwave frequencies in Dy-123 thin films

A pronounced peak in the microwave (at frequency 9.55 GHz) surface resistance, R s vs. T plot (where T is the temperature) has been observed in epitaxial DyBa2Cu3O7−y superconducting thin films in magnetic fields (parallel to c-axis) in the range 2 to 8 kOe, and temperatures close to the superconducting transition temperature T c(H). Our data suggest that the nature of peaks observed in the two films is different, thereby indicating different defect structures in the films.

Anisotropic superconductivity in epitaxial MgB 2 films

We measure the in-plane electrical resistivity of epitaxial MgB 2 thin films in magnetic fields to 60 T and estimate the superconducting upper critical field H p c(0)≈24±3 T for field oriented along the c-axis, and H ρ ab(0)≈30±2 T in the plane of the film. We find the zero-temperature coherence lengths ξ c(0)≈30 A ̊ and ξ ab(0)≈37 A ̊ to be shorter than the calculated electronic mean free path l≈100±50 A ̊ , which places our films in the clean limit. These large upper critical fields make MgB 2 a strong candidate for technological applications.

Peak effect in laser ablated DyBa2Cu3O7−δ films at microwave frequencies at subcritical currents

In this article we report the observation of a peak in the microwave surface resistance (at frequencies ∼10 GHz) of laser ablated DyBa2Cu3O7−δ films in magnetic field ranging from 2 to 9 kOe (∥c) close to the superconducting transition temperature [Tc(H)]. The exact nature of the peak is sample dependent but it follows a general behavior. The peak shifts to lower temperature when the magnetic field is increased. It has strong frequency dependence and the peak is pronounced at frequencies close to the depinning frequency of the flux line lattice. From the observed temperature and field dependence we argue that this peak is associated with the order–disorder transition of the flux line lattice close to Tc(H).

Peak effect in a superconductingDyBa2Cu3O7−δfilm at microwave frequencies

We report the observation of a peak in the microwave (9.55 GHz) surface resistance in an epitaxial DyBa2Cu3O7-y superconducting film in magnetic fields (parallel to the c axis) ranging between 0.2 to 0.9 Tesla. Such a peak is absent in the measurements done in zero-field. The temperature and field dependence of the peak suggests that this peak could be associated with the peak effect phenomenon reflecting the order-disorder transformation in the flux-line lattice. A strong dependence of this peak effect at frequencies close to the depinning frequency of the flux line lattice is observed.

Dynamic range of materials for the magneto-optic imaging of magnetic fields

The range of rearrangement of the natural domain structure of epitaxial garnet ferrite films in magnetic fields produced by conventional recording magnetic media was calculated using numerical methods. Maximum and minimum periods of the recording medium signalograms that could be imaged using the fillm domain rearrangement were obtained as functions of the recording medium and film parameters.

Longitudinal and transverse magnetizations in micron-thick Y-Ba-Cu-O films in nearly parallel magnetic fields

We have studied the magnetization in c-axis oriented-micron-thick Y-Ba-Cu-O (YBCO) films in magnetic fields oriented nearly parallel to the ab plane. The orientation dependence of the magnetic moment is dominated by shape anisotropy effects and this moment is contributed by its component along the c-axis for most of the cases. However, when the applied field is oriented very close to the ab plane, it is found to have a hysteretic component contributed by in-plane magnetization due to flux penetration along the ab plane. We measured longitudinal (along the field), and transverse (orthogonal to the field) moments to elicit in-plane magnetic response. At high fields, the penetrating flux in the ab plane decreases the critical current density in the ab plane, which results in the reduction of c-axis magnetic moment.

Hysteresis losses in thick YBCO films: a linear componential analysis of magnetization in nearly parallel magnetic fields

We investigated the magnetization ( M) hysteresis loops of micron-thick, c-axis-oriented YBCO films in magnetic fields applied nearly parallel to the film surface, θ⩽7 °, where θ is an angle between magnetic field and the film surface. It is expected from the film geometry with a large aspect ratio (width/thickness) that M is dominated by the perpendicular magnetization ( M c) due to the shielding current flowing in the ab plane. However, we have first demonstrated that there is considerable contribution from the magnetization along the ab plane ( M ab ) when a medium field (≈0.1 T) is applied very close to the film surface ( θ⩽0.4–2.0 °, depending on temperature). We investigated the temperature and field dependence of hysteretic magnetization to outline the behavior of the hysteresis loss in an inclined field in practically interesting conditions.

Peak effect at microwave frequencies in swift heavy ion irradiated YBa2Cu3O7-δthin films - investigation of vortex dynamics

ABSTRACTThe vortex dynamics at microwave frequencies in YBa2Cu3O7-δ(YBCO) films has been studied. We observe a peak in the microwave surface resistance Rs vs. T (temperature) plots at 4.88 GHz in some films in magnetic fields (upto 0.8 T) whereas a few films do not show a pronounced peak in their surface resistance. This is associated with the ‘peak-effect’ phenomenon and reflects the order-disorder transformation of the flux-line lattice near the transition temperature. Introduction of artificial pinning centers like columnar defects as a result of irradiation with 200 MeV Ag ion leads to the suppression of the peak in films exhibiting the ‘peak-effect’. Interestingly, a peak is seen to develop in those films that initially did not show a peak in the surface resistance before irradiation. These results and the dynamics of the vortices at microwave frequencies for the unirradiated and irradiated films will be discussed.

Effect of silver doping on the transport properties of epitaxial YBa 2Cu 3O 7−x thin films

Epitaxial YBa 2Cu 3O 7 (YBCO) thin films doped with 5–20 wt % Ag have been grown “ in situ” at high oxygen pressure by a dc sputtering technique on (001) SrTiO 3 substrates. Critical current densities, J c, were measured in 5 wt % Ag-doped YBCO films in magnetic fields up to 6 T, and were found to be greater than the values obtained for undoped samples. Current-voltage (I–V) characteristics were used to investigate the vortex phase transition, in magnetic field of 6 T applied parallel to the c-axis. The ϱ-j curves scale according to the 3D vortex-glass (VG) model with values of the critical exponents similar to those found for undoped YBCO samples (ν=1.4 and z=4.87).

Double sign reversal of the vortex Hall effect inYBa2Cu3O7−δthin films in the strong pinning limit of low magnetic fields

Measurements of the Hall effect and the resistivity in twinned YBa2Cu3O7-delta thin films in magnetic fields B oriented parallel to the crystallographic c-axis and to the twin boundaries reveal a double sign reversal of the Hall coefficient for B below 1 T. In high transport current densities, or with B tilted off the twin boundaries by 5 degrees, the second sign reversal vanishes. The power-law scaling of the Hall conductivity to the longitudinal conductivity in the mixed state is strongly modified in the regime of the second sign reversal. Our observations are interpreted as strong, disorder-type dependent vortex pinning and confirm that the Hall conductivity in high temperature superconductors is not independent of pinning.

Microwave resistivity at 48GHz in high-Tc superconductor films in magneticfields

We consider the field dependence of the microwave resistivity inhigh-Tc superconductors. We present field-dependent microwaveresistivity measurements at 48 GHz on thin YBa2Cu3O7-δ and Bi2Sr2CaCu2O8+x films. The field dependence of the microwaveresistivity cannot be satisfactorily described in terms of a singlemodel for the flux motion when both materials are considered. Weintroduce and discuss a simple model that incorporates the effect ofthe enhanced field-induced quasiparticle increase in asuperconductor with lines of nodes in the gap, together with viscousflux motion. A good description of the data is obtained, for YBa2Cu3O7-δ as well as for Bi2Sr2CaCu2O8+x.

Magnetic-field oscillations of the critical current and the pinning force in PbTe/PbS semiconductor superlattices and YBa2Cu3O7–δ films

The magnetic-field dependences of the critical current I c and the pinning force F p in single-crystal semiconductor PbTe/PbS superlattices on KCl and YBa2Cu3O7–δ films in magnetic fields oriented perpendicular to the plane of the samples or parallel to the current were investigated. Oscillations of I c and F p were observed for superlattices with a parallel orientation of the magnetic field and with two directions of the field for the YBa2Cu3O7–δ film. A model was proposed for the vortex structures which correspond to extrema of the pinning force in superlattices. It was shown that the single points (extrema and points of inflection) of the field dependences of F p for superlattices and a YBa2Cu3O7–δ film appear for critical values of the magnetic field equal to H cr = (p/q)H 0, where p and q are integers, H 0 = 838.37 Oe, and H 0 = ch/π eR 0 2 is determined by the length R 0 = 88.607 nm, somewhat less than the reciprocal of the Rydberg constant R ∞ = me 4/πħ3 c (R ∞ −1 = 91.127 nm). It was inferred on the basis of published data that the temperature and magnetic-field dependences of the properties of superlattices and HTSC materials follow general laws.

Studies of mesoscopic lattices forming with magnetic fluid

The high-quality magnetic fluid composition is capable of forming two-dimensional lattices of concentrated magnetic particle columns in a thin film in magnetic fields. The extraordinary lattices, a kind of novel mesoscopic system, have been explored with optical microscopy, digital imaging, and computer–video technique in this study. The two-dimensional lattices present hexagonal phase with exotic topological defects due to the structure distortion under excitations. The ordering of the 2D lattices are classified with positional and bond-orientational correlation functions. Some dynamical observations of topological defects are also made in this study.

パルスレーザー堆積法を用いて磁場下で作製した透明導電膜

The pulsed laser deposition (PLD) method has furnished useful means to fabricate films with noble and highly efficient properties. However, when the equipment with an excimer laser of intricate and expensive features is used to fabricate the films, it will bring about the raising of cost. Therefore, we paid attention to the PLD method by Nd : YAG laser with simple and inexpensive features and performed to prepare films in magnetic fields using Nd : YAG laser (fundamental 1064 nm and SHG 532 nm), in which it was aimed to suppress the generation of droplet and to shorten the preparation time. From these results, it was confirmed that by preparing in the magnetic field, it was able to fabricate the films with properties of low resistivity and high transparency. Moreover, from XRD measurements and SEM observation, the reforming of surface morphology due to improvement in crystallinity, was found. These effects were remarkable in the films prepared using the wavelength of 532 nm.

Crossover from a three-dimensional to purely two-dimensional vortex-glass transition in deoxygenatedYBa2Cu3O7−δthin films

Current-voltage $(I\ensuremath{-}V)$ characteristics were used to investigate the response of the vortex-glass (VG) phase transition in high-quality epitaxial ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ films in magnetic fields up to 7 T. We show that varying the oxygen content, the scaling analysis reveals a crossover from three-dimensional (3D) to a pure 2D VG transition with ${T}_{g}=0.$ At small oxygen deficiencies $(7\ensuremath{-}\ensuremath{\delta}=6.75),$ the $\ensuremath{\rho}\ensuremath{-}j$ curves scale according to the 3D VG model, which cannot be distinguished from a Bose-glass model from a scaling analysis with the magnetic field applied parallel to the c axis. At a lower oxygen content $(7\ensuremath{-}\ensuremath{\delta}=6.48),$ the VG phase transition behaves analogous to the highly anisotropic ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8}$ samples, showing a quasi-2D VG transition. For further deoxygenated samples $(7\ensuremath{-}\ensuremath{\delta}=6.4),$ the result is consistent with a pure 2D vortex-glass model similar to that observed in the even more anisotropic ${\mathrm{Tl}}_{2}{\mathrm{Ba}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8}$ thin films. The estimated value of the anisotropy in high-quality oxygen-depleted samples is comparable to that of the highly anisotropic superconductors.

Vortex motion noise inYBa2Cu3Oxfilms before and after heavy-ion irradiation

We have studied vortex motion noise in epitaxial YBa{sub 2}Cu{sub 3}O{sub x} films in magnetic fields before and after introducing columnar defects into the film by heavy-ion irradiation. Vortex motion exhibited a noise peak, which occurred at a field-dependent temperature. We found an {ital increased} noise peak magnitude after irradiation, and interpreted it as an increased bundle size, probably due to an increased {ital length} of vortex segments due to the interaction with pinned vortices in columnar defects. The magnetic field and the current dependence of the noise provided additional insights into the effects of columnar defects. After irradiation, the noise peak was almost independent of magnetic field, {ital B}, when it is less than about half of the matching field B{sub {phi}} but dropped by a factor of 3 for B{approximately}2B{sub {phi}}. On the other hand, for B{lt}0.5B{sub {phi}}, the bundle size was strongly current dependent at small current in the irradiated sample, but such a current dependence disappeared at higher currents or fields and was absent in the unirradiated sample. {copyright} {ital 1999} {ital The American Physical Society}

Magnetic field and current density dependence of the mixed-state Hall effect in Bi 2Sr 2CaCu 2O x

We report on measurements of the mixed-state Hall effect in Bi 2Sr 2CaCu 2O x thin films in magnetic fields ranging from B=60 mT to B=1 T and current densities j up to 3 MA cm −2. To reduce the problem of sample heating, we employed a pulsed current technique and developed a new heating correction procedure. We observe a double sign reversal of the Hall resistivity ρ yx in the mixed state, resulting in two peaks which both depend on B and j. The position of the sign changes only varies with B, but is found to be independent of j. The Hall conductivity σ xy turns positive again in the superconducting regime and dramatically increases towards lower temperatures and current densities, as the pinning is reduced by intense currents.

Far-infrared properties of superconducting YBa 2Cu 3O 7- δ films in high magnetic fields

We report the far-infrared properties of superconducting ab plane-oriented YBa 2Cu 3O 7- δ films in magnetic fields of up to 27 T. The applications of magnetic field (with H perpendicular to the ab plane and with unpolarized light) at low temperature produces no discernible field dependence. This observation differs from other previous far-infrared measurements in this temperature range. Only at fields and temperatures where the dc resistance is not zero – on account of dissipative flux motion – is a field-induced effect observed.

Transport Phenomena in the Mixed and Normal State of (Bi1.6Pb0.4)Sr2Ca2(Cu1-xFex)3Oy Epitaxial Thin Films

We had performed a study on magnetoresistivity, Seebeck, Nernst and Hall effects in the mixed and normal state for Bi2223 thin films in magnetic fields between 0 and 5 T and in the temperature range 5–300 K. The critical temperatures, the Hall concentration, the Nernst and Seebeck coefficients depend strongly on the iron content in the samples. From our experimental data in the mixed state and fluctuation regime, the upper critical field slope (dBc2/dT )=-2:55 T/K was obtained, corresponding to ab-plane coherence length ξab=14 Å. The experimental data are in agreement with the predictions of the time-dependent Ginsburg–Landau theory.