Journal of Superconductivity and Novel Magnetism最新文献

We present our findings on the room temperature (RT) soft ferromagnetism (FM) of the sol-gel-prepared Co-doped barium titanate (BaTiO₃) nanoparticles with two distinct Co concentrations (0.25 mol% and 0.5 mol%), that is appropriate for spintronic applications as evidenced by experimental observations. X-ray diffraction investigation revealed that the produced samples, which had diameters less than 100 nm, belonged to the pseudo-cubic phase of the BaTiO₃ structure and did not exhibit any signs of the Co cluster or any other Co oxides. UV-visible absorption spectra demonstrate that the optical response is red shifted and the bandgap energy is lowered when Co is incorporated into the BaTiO₃ lattice. The inclusion of cobalt ions may have brought about a change in size or an increase in surface defects, as evidenced by the PL spectra, which show that the intensity of emission peaks changes as the dopant concentration increases. In the 0.25 mol% Co-doped BaTiO₃ sample, the FM behavior is clearly visible along with the paramagnetic (PM) phase at RT. Significantly, it becomes apparent that as the doping concentration is raised to 0.5 mol%, the saturation magnetization is reduced, and a pure phase of soft FM is obtained. This soft FM feature witnessed in 0.5 mol% doped BaTiO₃ with low coercivity (96.8 Oe) and low saturation magnetization (9.7 × 10⁻³ emu/g) is likely due to oxygen vacancies and could set out as a promising magnetic material for possible spintronic applications.

Leggett mode is a collective excitation of the phase difference of superconducting condensates whose energy is determined by the strength of Josephson coupling between them. Since the Leggett mode does not perturb the symmetry of Cooper pairs, it should be sensitive to the spin symmetry of the condensate order parameters. Using the point-contact (Andreev) spectroscopy, we have revealed their presence in a three-gap superconducting state realized in MgB₂/La_0.67Sr_0.33MnO₃ nanocomposite. Two of them, Δ_π and Δ_σ-enh, are directly connected to intrinsic gaps in MgB₂, with a slight increase in the larger σ-gap probably due to a spin-triplet pairing contribution. The third spin-triplet gap Δ_tr is intrinsic to the La_0.67Sr_0.33MnO₃ compound while manifests itself only when it is proximitized to a superconductor. In such nanocomposite, the appearance of periodic Leggett peaks of two symmetry types is expected to be associated with the spin state of superconducting condensates. The idea of our experiments was to use two types of counter-electrodes, an ordinary normal metal and a spin-polarized conductor. In the first case, the Leggett mode associated with two spin-singlet gaps would be dominant while, due to spin selectivity, excitations of the relative phase for two triplet-spin order parameters are expected to prevail in the second case. In the work, we confirmed this assumption by discovering that the period of Leggett peaks in contacts of the nanocomposite with an Ag tip turned out to be twice as large as those for contacts with La_0.67Sr_0.33MnO₃ and La_0.67Ca_0.33MnO₃ counter-electrodes.

Density-functional theory (DFT) is utilized to study the crystal structure, geometry, and magnetic and electronic properties of the triple perovskites Ba₃MRu₂O₉ (M = Fe, Co, and Ni) in hexagonal phase with space group P6₃/mmc. Generalized gradient approximation plus Hubbard potential is found to be an effective potential for the treatment of these perovskites. Spin-orbit coupling with Hubbard U (GGA+SOC+U) is also applied to analyze its effect on the understudy compounds. The optimized crystal structures and geometries are consistent with the experimental reported results. The stability of these perovskites is described by cohesive and formation energies. The antiferromagnetic (AFM) nature of all these perovskites is confirmed by stable magnetic phase energies and magnetic susceptibility. The electronic band profiles in the AFM phase and electrical resistivities confirm that these perovskites are metallic in nature. Metallicity as well as magnetism in these compounds is due to d-state electrons of the M and Ru atoms. The metallic AFM nature reveals that these compounds are promising materials for magnetic cloaking, high-speed switching devices, and spintronic applications.

The path dependence of the magnetocaloric effect (MCE) in CoS(_{1.76})Se(_{0.24}) has been studied. A field-induced paramagnetic (PM)-ferromagnetic (FM) transition results in 4.6 J/kg-K peak value of isothermal entropy change ((Delta)S(_{th})) for 90 kOe field change. Above 10 K, the temperature dependence of (Delta)S(_{th}) calculated from the forward curve (0 kOe–90 kOe) and that calculated from the reverse curve (90 kOe–0 kOe) are found to be similar, whereas at lower temperature, contrasting behaviour is observed due to the kinetic arrest of first-order magnetic transition.

Multicomponent rare earth intermetallic compounds Tb_0.33Ho_0.33Er_0.33Ni and Dy_0.33Ho_0.33Er_0.33Ni crystallize in orthorhombic FeB-type structure (Space group Pnma, No. 62, oP8) and order ferromagnetically at 59 K and 40 K (T_C) respectively. Hydrides of these samples show a presence of ~ 10-nm size nanoparticles with unit cell volume expansion. Magnetization measurements reveal that hydrides Tb_0.33Ho_0.33Er_0.33NiH_1.9 and Dy_0.33Ho_0.33Er_0.33NiH_1.9 remain paramagnetic from 300 K down to 5 K. Magnetization value at 5 K in 70 kOe field is ~ 5.1 µ_B/f.u. and 5.5 µ_B/f.u., respectively, for Tb_0.33Ho_0.33Er_0.33NiH_1.9 and Dy_0.33Ho_0.33Er_0.33NiH_1.9 samples. Despite the lack of ferromagnetic order, hydrides exhibit large low-temperature magnetocaloric effect with maximum isothermal magnetic entropy change values of about − 11.6 Jkg⁻¹ K⁻¹ at 14 K and – 12.9 Jkg⁻¹ K⁻¹ at 8 K respectively for 50 kOe magnetic field change.

In the present work, La³⁺ ion substituted strontium Z-type hexaferrites (Sr_3-xLa_xCo₂Fe₂₄O₄₁ (x = 0, 0.05, 0.10, 0.15, 0.20, and 0.25)) have been synthesized using solid-state reaction method. The effect of substitution on its structural and magnetic properties was investigated. X-ray diffraction (XRD) pattern confirms the formation of single-phase Z-type hexaferrite. The XPS spectra provide the evidence for formation of Fe²⁺ in La-substituted SrZ hexaferrites. FESEM micrographs of as prepared samples showed a reduction in grain size with the increasing La substitution. The behavior of substitution at various crystallographic sites was analyzed by Raman spectroscopy. The increase in saturation magnetization (M_s) and coercivity (H_c) was observed with increasing La content from x = 0 to x = 0.25.

This study uses density functional theory calculations to study the impact of pressure on the structural, elastic, and thermodynamic properties of CaRh₂P₂ and BaRh₂P₂ compounds. The equilibrium structural parameters closely match the experimental values. CaRh₂P₂ shows a greater reduction in lattice parameter “a” under pressure, while BaRh₂P₂ shows the opposite trend. The single-crystal elastic constants calculated for both compounds meet the criteria for mechanical stability under varying pressures up to 18 GPa. The study extends to polycrystalline elastic properties, including bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, and related properties, under pressures up to 18 GPa. The Pugh ratio, Cauchy pressure, and Poisson’s ratio indicate the ductile behavior of the title compounds. BaRh₂P₂ exhibits superconducting characteristics, unlike CaRh₂P₂, confirmed by interlayer PP bond length calculations. Debye’s quasi-harmonic model explores the temperature dependencies of various properties, with results that align well with elastic constant data, thus validating the results.

Perovskites represent distinctive materials suitable for both transport and optoelectronic applications, harnessing renewable resources to produce energy. In this study, the perovskite Li₂SnI₆ has been explored, focusing on a comprehensive analysis of its physical properties under strain. The encompassed investigation of the structural, elastic, electronic, optical, and thermoelectric characteristics of the studied compound. Utilizing density functional theory (DFT) implemented in the Wien2k package, we employed the LSDA+mBJ approximation to determine the exchange-correlation potential. The elastic constants and related parameters have been reported such as bulk modulus, shear modulus, Young’s modulus, anisotropy factor, Poisson’s ratio, and internal strain parameter for Li₂SnI₆ in its cubic structure. The electronic part reveals the semiconductor behavior of the studied compound and a decrease in gap energy with increasing pressure, reaching E_g = 0.2 eV for P = 12 GPa. Additionally, the absorption of optical factors lies in the ultra-violet (UV) region, noted at P = 12 GPa, with an intensity of 230 × 10⁴ cm⁻¹, which makes this material suitable for photovoltaic devices. Furthermore, we delved into the electrical conductivity, Seebeck coefficient, and electronic part of thermal conductivity. The results indicated that the compound demonstrates p-type behavior, as evidenced by positive values for the Seebeck coefficient with the highest value of 240 µV/K observed for P = 4 GPa. The analysis of thermoelectric and optical properties suggests that the studied perovskite is well-suited for applications in renewable energy.

Angular-dependent magneto-optical Kerr effect (MOKE) and coplanar waveguide ferromagnetic resonance (CPW-FMR) measurements were performed to unravel the nature of anisotropy present in Ni(_{80})Fe(_{20}) (Py) thin film. The “in-plane” angular variation of coercive field ((H^{IP}_{c})) and resonance field ((H^{IP}_{r})) confirms the magnetic anisotropy is negligible, where the spins are confined to the plane of the Py film. The variation of resonance field in “out-of-plane” geometry, (H^{OP}_{r}), strongly indicates the presence of “out-of-plane” uniaxial anisotropy in the Py thin film. Also, the inverse spin Hall effect (ISHE) technique is employed to measure spin pumping-induced DC voltage, V(_{ISHE}), generated across the Py/Pt bilayer. The line shape analysis method has been utilized to distinguish ISHE and spin rectification contributions. The measured V(_{ISHE}) at low (4 GHz) and high (35 GHz) frequencies confirm the pure spin current injected through the Py-Pt interface due to spin pumping using CPW-FMR setup, which has a direct bearing on the realization of quantum metrology through the spin current quantity.

Heusler compounds stand as a versatile class of intermetallics with extraordinary electrical, magnetic, and thermoelectric properties that render them indispensable in various applications. This study delves deeply into the mechanical, dynamical, electronic, magnetic, and transport characteristics of Mn(_2)CoGe and Mn(_2)CoSb compounds. Both compounds display mechanical stability, ionic bonding, and a ductile nature. The positive phonon frequencies further affirm their dynamical stability. Moving to the electronic structure calculations, our assessments encompass magnetic moment, band structure, and density of states, highlighting the distinctive half-metallic characteristics inherent in these compounds. Transport coefficient calculations for both spin channels demonstrate the compounds’ relative constancy in terms of Seebeck coefficient and electrical conductivity despite temperature fluctuations. The observed spin polarisation and thermoelectric response underscore the promising suitability of these compounds for future applications in spintronics and thermoelectrics. While the achieved maximum thermoelectric figure of merit value of 0.2 holds potential for their thermoelectric capabilities, further experimental validations are imperative for a comprehensive evaluation.