Journal of Superconductivity and Novel Magnetism最新文献

Structural, magnetic, and dielectric properties of (x)SrFe₁₂O₁₉-(1-(x))Ba_0.85Ca_0.15Ti_0.9Zr_0.1O₃ multiferroic composite prepared by sintering the composite mixture of sol-gel synthesized SrFe₁₂O₁₉ (SrF) and Ba_0.85Ca_0.15Ti_0.9Zr_0.1O₃ (BCTZ) are reported. Structural parameters (lattice parameter, bond length, and lattice strain) of parent phases in their pure and composite forms are correlated to indicate the lattice interaction between the two phases. The magnetic moment per gram of SrF (({M}_{SrF})) in the composite is higher than that in the SrF, related to the changes in the Fe-O-Fe bond angles. The room temperature dielectric response of the composites in the 100 Hz–10 MHz frequency range is modeled by the Cole–Cole relaxation and Jonscher power law equations to mark the different contributions (ferroelectric dipoles, charge carriers).

Impact of shot peening on SS347 tube has been investigated using MagStrics, a magnetostrictive sensing (MsS) device comprising of rapidly quenched ribbon as sensor element. Two tubes of SS347 have been considered in pre- and post-shot peened state. Annealed ribbon as sensor element showed enhanced MsS signal. Using the annealed ribbon as sensor element, the MsS signal amplitude in shot peened tube was found to be distinctly different from un-peened sample. This was associated to magnetic phase evolutions in the pipe internal surface due to shot peening. Such phenomena have been endorsed through SEM–EDX compositional analysis and correlated through simulations using COMSOL Multiphysics.

Nowadays, the concept of non-trivial topological protection and the nanoscale size of nanomagnetic particles constitute a major area of research. Due to topological protection stability, nanoscale size, and the requirement of low spin current density for motion, skyrmions have attracted great attention in next-generation spintronic devices as robust information carriers. We study the motion of an isolated magnetic skyrmion with induced interfacial Dzyaloshinskii-Moriya interaction (iDMI) instigated by spin waves and driven by spin current with variation in different parameters in a nanotrack of finite length using micromagnetic simulations. It is found that the magnetic skyrmion moves in the same direction as the direction of propagation of the spin waves. The skyrmion initially experiences an acceleration in its motion; thereafter, the velocity decreases exponentially. The motion of the magnetic skyrmion initiates as the momentum of the spin wave gets transferred to it. The motion of the magnetic skyrmion is found to be significantly dependent on the variation of parameters like frequency and amplitude of the incident spin waves, as well as the damping parameter and the strength of the applied spin-polarized current. The results obtained in this work could become useful to design skyrmion-based spintronic information-carrying and storage devices.

Conventional solid-state reaction method has been cautiously employed to prepare the Ba_0.75Sr_0.25Ti_1−xMn_xO₃ ceramic where Sr was firmly doped at the Ba site and Mn was doped with different densities at the Ti site. Since the performance of materials varies with frequency, electric field, and temperature, we have elucidated the various features of the synthesized samples for the sake of scientific benefit in the fields of microelectronics, telecommunications, and spintronics. Structural and morphological features of the ready samples were examined by X-ray diffraction and scanning electron microscopy (SEM). The crystal's tetragonal behavior was verified by XRD analysis, and with the increment of Mn content, the volume of the unit cell is little changed. It is clear from the SEM images that the grain size of the prepared samples increases with Mn doping. The dielectric properties of Ba_0.75Sr_0.25Ti_1−xMn_xO₃ were measured by dielectric constant and AC conductivity in a wide range of frequency from 1 kHz to 10 MHz. This result also explores that the dielectric constant rises with the concentration of Mn, most significantly for the 20% Mn substitution with Ti. We also found from the experimental result that the dielectric constant is high in the frequency range of 1–10 kHz. The magnetic permeability of the prepared sample increased with 10% and 20% of Mn replacement. Ferromagnetic features with a weak coercive field and the increased ferromagnetic order with rising Mn concentrations of the prepared samples were confirmed by VSM data analysis. The developed multiferroic materials can be employed in future spintronic devices like spin transistors, sensors, spin diodes, and memory devices.

In this paper, we report a systematic study on effect of film thickness and substrate temperature on structural and magnetic behaviour of Fe-Ga films with Cu buffer layer, deposited on Si and Si/SiO₂ substrates at room and high substrate temperatures. Grazing incidence X-ray diffraction studies reveal that all the films are crystalline with disordered alpha-Fe phase, which is BCC A2 phase. At 300 °C of substrate temperature, films deposited on Si/SiO₂ substrate found to nucleate L1₂ phase from matrix of A2 phase, which is not seen in Si based films. Irrespective of substrate material, Fe-Ga films found to exist in dual phases at 500 °C substrate temperature. Lattice strains of the films were calculated from X-ray diffraction patterns, using Williamson-Hall method. From X- ray reflectivity analysis of all the films, film density, thickness and roughness of Fe-Ga layer and buffer layer were obtained after fitting the reflectivity data. Presence of an oxide layer is also evident from reflectivity fitting analysis. From magnetization studies it is clear that, all the films exhibited strong in-plane anisotropy. Saturation magnetization of films was found to vary with change in film density and oxide layer thickness of films. Saturation magnetization of films deposited on Si substrates found to decrease with decrease in film density. Coercivity of films found to vary with change in crystallite size, interface roughness and lattice strain of films. Films deposited on Si substrates are sensitive to strain with change in film thickness and films deposited on Si/SiO₂ substrates are sensitive to strain with change in deposition temperature. Coercivity in films found to decrease with decrease in film roughness, increase in crystallite size and lowering the tensile lattice strain.

In this paper, we have investigated the magnetic and magnetocaloric characteristics of a La₂MnNiO₆ composite, in conjunction with La₂MnCoO₆. This composite consists of two phases of double perovskite materials. Employing the mean-field approximation, we successfully modeled how magnetization and the change in magnetic entropy vary with temperature under different magnetic fields in our samples. This phenomenological model helped us also plot the maximum magnetic entropy change (-ΔS_M)_max, full width at half-maximum δT_FWHM, and relative cooling power (RCP). Our analysis has revealed an optimal plateau-type magnetocaloric effect near room temperature, corresponding to a specific composition x between 0.2 and 0.5. Ultimately, this theoretical model lets us predict the magnetic and magnetocaloric behavior of composite materials, providing a foundation for future studies.

The perovskite La₂ZnMnO₆ was successfully synthesised using the conventional solid-state reaction. X-ray diffraction shows that the perovskite La₂ZnMnO₆ crystallizes in a monoclinic structure P2₁/n space group, where Zn and Mn atoms are regularly distributed. The Raman spectrum result reveals three peaks at 696 cm⁻¹, 655 cm⁻¹ and 505 cm⁻¹, corresponding to the A_g stretching mode, B_g anti-stretching, and bending vibrations modes of Ni/Co-O and Mn-O bonds in the structure. The experimental value of the band gap energy was calculated using Tauc’s formula and the result reveals a semiconducting behaviour. We investigated the structural, elastic, magnetic, and electronic properties using the spin-polarized density functional theory. The partial density of state indicates that the material exhibits a antiferromagnetic semiconducting behaviour. The antiferromagnetic ordering is explained by the super-exchange interaction between empty e_g orbitals of Mn⁴⁺( ({t}_{2 g}^{3})({e}_{g}^{0})). The obtained Neel temperature is T_N ∼ 28 K which is comparable with the experiment results. Elastic constants and their derivative parameters show a high mechanical stability of this material with a ductile nature. The investigation of the transport properties encompassed an analysis of the electrical conductivity, the figure of merit, the Seebeck coefficient, and thermal conductivity. The results show that electronic and thermal conductivities increase linearly with temperature. The computed values of the figure of merit are close to unity, suggesting that this material is a promising candidate for thermoelectric application.

It is shown that many anomalies observed in underdoped cuprates, including anomalous spectral weight transfer and a large pseudogap, appear to have a common nature due to both the cluster structure of the underdoped phase and the specific mechanism of superconducting pairing. The combined action of these factors leads to the fact that at a temperature T lying in a certain temperature range T_c < T < T*, the crystal contains small isolated clusters that can exist both in superconducting and normal states, randomly switching between them. In this case, below T_c with a very high probability, the cluster is in a superconducting state, and above T*, it is in a normal state, and the interval T_c < T < T* is the region of existence of the so-called pseudogap phase. The temperatures T_c and T* for YBa₂Cu₃O_6+δ were calculated depending on the doping level δ. The calculation results are in good agreement with the experiment without the use of fitting parameters. At a given T in the same temperature range, the time sequence of randomly arising superfluid density pulses from each cluster can be represented as a random process. The effective width Δω_eff of the spectrum of such a random process will be determined by a correlation time, i.e., the characteristic time between successive on/off superconductivity in two different clusters. This time, according to the estimate, is ~ 10⁻¹⁵ s, which corresponds to Δω_eff ~ 1 eV and explains the effect of spectral weight transfer to the high-frequency region. This approach also makes it possible to explain other anomalies observed in the vicinity of T_c: the reversibility of magnetization curves in a certain temperature range below T_c, the anomalous Nernst effect, and anomalous diamagnetism above T_c.