9 research outputs found
Tailoring phase slip events through magnetic doping in superconductor-ferromagnet composite films
The interplay between superconductivity (SC) and ferromagnetism (FM) when
embedded together has attracted unprecedented research interest due to very
rare coexistence of these two phenomena. The focus has been mainly put into the
proximity induced effects like, coexistence of magnetism and superconductivity,
higher critical current, triplet superconductivity etc. However, very little
attention has been paid experimentally to the role of magnetic constituent on
triggering phase slip processes in the composite films (CFs). We demonstrate
that less than 1 at. % of magnetic contribution in the CFs can initiate phase
slip events efficiently. Due to advanced state-of-the-art fabrication
techniques, phase slip based studies have been concentrated mainly on
superconducting nanostructures. Here, we employ wide mesoscopic NbGd based CFs
to study the phase slip processes. Low temperature current-voltage
characteristics (IVCs) of CFs show stair-like features originated through phase
slip events and are absent in pure SC films. Depending on the bias current and
temperature, distinct regions, dominated by Abrikosov type vortex-antivortex
(v-av) pairs and phase slip events, are observed. The results presented here
open a new way to study the phase slip mechanism, its interaction with v-av
pairs in two dimensions and hence can be useful for future photonic and
metrological application
Ultrasensitive interplay between ferromagnetism and superconductivity in NbGd composite thin films
A model binary hybrid system composed of a randomly distributed rare-earth
ferromagnetic (Gd) part embedded in an s-wave superconducting (Nb) matrix is
being manufactured to study the interplay between competing superconducting and
ferromagnetic order parameters. The normal metallic to superconducting phase
transition appears to be very sensitive to the magnetic counterpart and the
modulation of the superconducing properties follow closely to the
Abrikosov-Gorkov (AG) theory of magnetic impurity induced pair breaking
mechanism. A critical concentration of Gd is obtained for the studied NbGd
based composite films (CFs) above which superconductivity disappears. Besides,
a magnetic ordering resembling the paramagnetic Meissner effect (PME) appears
in DC magnetization measurements at temperatures close to the superconducting
transition temperature. The positive magnetization related to the PME emerges
upon doping Nb with Gd. The temperature dependent resistance measurements
evolve in a similar fashion with the concentration of Gd as that with an
external magnetic field and in both the cases, the transition curves accompany
several intermediate features indicating the traces of magnetism originated
either from Gd or from the external field. Finally, the signatures of magnetism
appear evidently in the magnetization and transport measurements for the CFs
with very low (less than 1 at. %) doping of Gd
Low-frequency dielectric processes in deformed helix ferroelectric liquid crystals
A low-frequency dielectric relaxation mode in deformed helix ferroelectric liquid crystal (DHFLC) has been observed at the interface of strongly rubbed substrates and DHFLC material which may find applications in low power consumption FLC devices. The surface-induced dielectric relaxation process at the interface of DHFLC and substrate is called the partially unwound helical mode (p-UHM) due to the unwinding of the helical structure at this interface. After investigation of the material under various parameters such as temperature, variation of the amplitude of probing ac voltage and dc bias voltage, the relaxation frequency of p-UHM is found to be shifted towards Goldstone mode and merged with it. The relaxation frequency of Goldstone mode is found to decrease, whereas the relaxation frequency of p-UHM process increases with the increase in temperature of DHFLC. Finally, both the modes merge and the resultant relaxation frequency is found to be lower than Goldstone mode in SmC* phase. It seems that phason mode and partial helical unwinding mode are coupled together due to dipole moment that is resulting in a new relaxation frequency. p-UHM process is significant for low-power displays and non-displays applications like a part of sensor where weak electric signal is required to be realized without pre-amplification
Collective dielectric processes at the transition temperature of the Sm-C* and Sm-A* phase in a ferroelectric liquid crystal
An anomalous dielectric relaxation process, called the partially unwound helical mode (p-UHM), is a collective dielectric process apart from the well known Goldstone and soft mode process; it is studied in the smectic C* (Sm-C*) phase and at the transition temperature of the Sm-C*-Sm-A* phase in the ferroelectric liquid crystal (FLC) material. To avoid the surface effect, a thick cell of 40 mu m thickness was prepared with highly rubbed surfaces of the ITO substrates. It has been observed that the dielectric properties in Sm-C* and at the T-c temperature are dominated by the p-UHM process which is dependent on an applied oscillating field in the Sm-C* phase. The probing ac and dc bias field dependences of all these collective dielectric processes have been reported in the Sm-C* and Sm-A* phases of FLC materials
Dielectric relaxation process of a partially unwound helical structure in ferroelectric liquid crystals
The fluctuations of unwound helical structure have been observed in deformed helix ferroelectric liquid crystal (DHFLC) and conventional FLC sample cells. The helix is partially unwound by strong anchoring on the substrates. In such sample cells, the helical decarlization lines are not observed in the texture under crossed polarized microscope. The dielectric spectroscopy is employed to observe the behavior of dielectric relaxation processes in these sample cells. A dielectric relaxation process is observed at a lower frequency than the Goldstone mode processes in DHFLC and FLC, which we call partially unwound helical mode (p-UHM). However, the p-UHM process is not observed in the sample cell in which the helical lines appear. The application of various amplitudes of probing ac voltages on this mode has shown the higher frequency shift, i.e., the larger the amplitude of ac voltage, the higher is the relaxation frequency of p-UHM. At sufficient amplitude of applied probing ac voltage, the p-UHM merges with the Goldstone mode process and is difficult to detect. However, the Goldstone mode relaxation frequency is almost independent of the cell geometry and sample configuration. The electro-optical behavior of the p-UHM has also been confirmed by electro-optical technique. The dielectric relaxation of UHM at a frequency lower than the Goldstone mode is interpreted as the fluctuation of partially unwound helix
Ultrasensitive interplay between ferromagnetism and superconductivity in NbGd composite thin films
A model binary hybrid system composed of a randomly distributed rare-earth ferromagnetic (Gd) part embedded in an s-wave superconducting (Nb) matrix is being manufactured to study the interplay between competing superconducting and ferromagnetic order parameters. The normal metallic to superconducting phase transition appears to be very sensitive to the magnetic counterpart and the modulation of the superconducing properties follow closely to the Abrikosov-Gor'kov (AG) theory of magnetic impurity induced pair breaking mechanism. A critical concentration of Gd is obtained for the studied NbGd based composite films (CFs) above which superconductivity disappears. Besides, a magnetic ordering resembling the paramagnetic Meissner effect (PME) appears in DC magnetization measurements at temperatures close to the superconducting transition temperature. The positive magnetization related to the PME emerges upon doping Nb with Gd. The temperature dependent resistance measurements evolve in a similar fashion with the concentration of Gd as that with an external magnetic field and in both the cases, the transition curves accompany several intermediate features indicating the traces of magnetism originated either from Gd or from the external field. Finally, the signatures of magnetism appear evidently in the magnetization and transport measurements for the CFs with very low (<1 at.%) doping of Gd
Impact of twisted alignment on the smectic layer structure of ferroelectric liquid crystal
The twisted aligned cell of ferroelectric liquid crystal is assessed through electro-optical and dielectric spectroscopy and a comparison is made with antiparallel planar aligned cells of the same thickness around 8 mu m. The study has been carried in two types of twisted aligned samples, one is natural cooled sample in the heating chamber and another is slow cooled at the rate of 0.05 degrees C/min. The influential distinct results have been observed in natural cooled twisted cells. In natural cooled cells, the helicoidal structure at the surface and in the bulk of the cell is distinct and contributes separately to the response of the cell. On the other hand, at the same cooling condition in twisted cell, the smectic layers are in a twisted state resulting into a non-uniform helical structure, therefore, the partial helicoidal unwound structure at the surface and in the bulk of the cell are not observed contributing to the dielectric permittivity separately unlike in planar aligned cell. The twisted cell is found to induce the restoring force within the sample. However, the slow cooling cydes on the twisted cell changes to the strain free equilibrium state, whereas the behavior of the planar sample cell remains unchanged. The studies are significant for the display devices based on twisted alignment of FLC cells