Journal of Superconductivity and Novel Magnetism最新文献

(^{77})Se NMR measurements confirm that in Fe(Se,Te) a change in the type of nematic transition is observed near its complete suppression. We present the studies of structural phase transitions in FeSe(_{0.675})Te(_{0.3})S(_{0.025}) crystals. The data obtained indicate a significant change in the behavior of many characteristics during the transition in this composition compared to the case of the unsubstituted FeSe. Similar to Fe(Se,Te) with a close tellurium content, the resistivity at low temperatures for the studied FeSe(_{0.675})Te(_{0.3})S(_{0.025}) is proportional to the square of the temperature, while for pure FeSe below the structural transition it depends almost linearly on temperature. (^{77})Se NMR proves that these changes are associated with changes in the type of ordering. The NMR data showed a noticeable line broadening below the structural transition and an anomaly in the temperature dependence of the relaxation rate, which was not observed in FeSe. Our results confirm existence of the nematicity change point (NCP) in Fe(Se,Te) at a low Te content and make the phase diagram of quasi-binary Fe(Se,Te) compounds generally consistent with the phase diagram of FeSe under pressure. Thus, in terms of chemical pressure, the effect of isovalent substitution in the series of Fe(Te,Se,S) compounds on the type of ordering can be caused by the anisotropic part of the deformation.

The study of exchange bias in various types of systems received great attention due to widespread applications in numerous magnetoelectronic devices and, in particular, understanding and controlling exchange bias in single layer films becomes crucial in advancing the spintronics field. With this connection, we here present a study on the origin of the exchange bias in the Fe₃O₄ (t nm) films with a polycrystalline structure fabricated via magnetron reactive sputtering directly onto a Si(100) substrate at ambient conditions and its correlation with thickness of the films and cooling fields. Structural and morphological studies reveal single phase polycrystalline Fe₃O₄ films and the average roughness increases with increasing thickness of the films. Magnetic properties show typical ferromagnetic behavior in Fe₃O₄ film, but interestingly, a considerable exchange bias (EB) of 550 Oe is noticed in 30 nm thick Fe₃O₄ film at 10 K when subjected to field cool. In addition, Fe₃O₄ (30 nm) film exhibits a spontaneous exchange bias without any external applied field. These observations can be understood from the magnetic exchange coupling at the interfaces between the ferromagnetic Fe₃O₄ and antiferromagnetic FeO, and the existence of a FeO can be validated from the magnetic anomalies in thermomagnetization data. Furthermore, the magnetic anomalies fade out at higher film thicknesses due to reduced (increased) volume of FeO (Fe₃O₄), causing suppression in the EB effect. The variation of EB with cooling field and film thickness demonstrates the tunability of EB in single layer Fe₃O₄ film and its suitability for possible applications in spintronics.

Bi‒Sr‒Ca‒Cu‒O polycrystalline high-temperature superconductors with the 2–2-2–3 structure have been comprehensively studied, their properties have been described, and features of the small magnetic hysteresis in the investigated materials have been established. The small magnetic hysteresis is shown to be caused by the penetration of a magnetic flux into a superconductor and its capture in the region of boundaries between HTS crystallites and by Meissner currents flowing through these boundaries. It has been found that, at a certain magnetic prehistory, the small hysteresis collapses, i.e. its footprints disappear. This has been attributed to the interaction between two superconducting subsystems in the investigated polycrystalline HTS, specifically, the effect of the magnetic moments of HTS crystallites on the effective field in the regions of intercrystalline boundaries. The shape of the small magnetic hysteresis loop has been described within the critical state model.

Recent theoretically predicted strong anisotropic spin Hall effect (SHE) or inverse SHE (ISHE) in chiral antiferromagnetic compounds Mn₃X (X = Ge, Sn, Ga, Ir, Rh, and Pt) could potentially expand the horizons of the antiferromagnet spintronics; however, it has not been experimentally observed yet. For achieving this goal, we have first successfully fabricated high-quality Kagome phase Mn₃Sn films with smooth surface by a combination of room-temperature magnetron sputtering and high-temperate annealing. These Mn₃Sn films were proved to be epitaxially grown on MgO (110) single crystal substrate with a seldom reported (({1}{text{0}}stackrel{text{-}}{1}{text{0}})) orientation that could serve as a good platform for the studies of the crystalline orientation-related anisotropic phenomenon. Then, by employing spin pumping-induced inverse spin Hall effect (SP-ISHE) voltage measurements, we have experimentally proved the existence of crystalline orientation-related anisotropic ISHE with an amplitude of more than 35% in our Mn₃Sn films.

This study analyzes the variations within LaCrO₃ induced by diamagnetic gallium (Ga) substitution at the chromium (Cr) sites, exploring the consequential changes in both structural configuration and magnetic attributes. Through structural characterization employing X-ray diffraction (XRD) and scanning electron microscopy (SEM), the modified lattice parameters and crystalline structure resulting from Ga incorporation are revealed, shedding light on the structural and phase modifications within the material. The magnetic property investigations unveil the impact on the weak ferromagnetism intrinsic to LaCrO₃ and in Ga substituted samples. Additionally, this research scrutinizes the consequential shifts in entropy resulting from Ga substitution, offering insights into the material’s thermodynamic properties. The findings elucidate the intricate relationship between structural modifications and magnetic properties within perovskite oxides, providing valuable insights into the multifunctional effects of Ga substitution on LaCrO₃.

Fe-Si-B-Cu-Nb nanocrystalline alloys have been commercially applied at power electronics. However, few research works are focused on improving high-frequency magnetic properties in the alloys. In this paper, the effect of additional magnetic field annealing temperature on high frequency soft magnetic properties of Si-rich FeSiBCuNb nanocrystalline ribbon was investigated. The as-quenched FeSiBCuNb amorphous alloys were crystallized annealing at 550 °C × 60 min for precipitating nanocrystalline α-Fe(Si) phase. Then the crystallized annealed alloy cores carried out additional transverse magnetic field annealing, and the induced uniaxial anisotropy K_u gradually increases from 9.4 to 21.6 J/m³ with increasing the annealing temperatures from 360 to 520 °C. By comparison with the non-magnetic field annealing sample, the μ_e of nanocrystalline cores with extra field annealing reduces at about the range of 1–30 kHz but gets significant improvement at 50–200 kHz, the Q improves and P_s decrease at all frequencies of 1 ~ 200 kHz. After the magnetic field is annealed at 480 °C, the core achieves optimal high-frequency properties of μ_e = 37.9 k (f = 100 kHz), Q = 0.87, and P_s = 30.94 W/kg. The improvement of high-frequency properties in cores upon transverse magnetic field annealing can be attributed to the fact that the magnetic domains appear in a rectangular band arrangement and are perpendicular to the longitudinal direction of the ribbon. When the magnetic cores operate in a dynamic magnetization field, the periodic magnetization is mainly characterized by domain rotation.

Magnetostrictive bimorphs consisting of positive and negative magnetostrictive materials such as FeGa and Ni respectively were made in the form of (a) multilayers containing Si/Ni/FeGa and (b) stacking consisting of Ni/Si/FeGa by sputtering technique on Si substrates. While the thickness of the FeGa film was maintained at 200 nm for all the films, Ni films were grown with two different thicknesses, viz., 100 and 200 nm. Magnetostrictive response of these bimorphs was compared with FeGa unimorph deposited on Si. Structural studies indicated FCC and BCC structure for Ni and FeGa films respectively. Magnetization studies showed a decrease in saturation magnetization with increase in Ni content owing to the lower magnetization of Ni when compared to FeGa. Considerable enhancement in tip deflection has been observed in the bimorph structure when compared with pure FeGa film.

This article reports the successful synthesis of single crystalline two-dimensional thin flakes of NbSe₂. The XRD (X-ray diffraction) pattern of the grown crystal ensured its crystallization in a single phase with a hexagonal structure. The EDAX (energy dispersive X-ray analysis) endorsed the stoichiometry of the as-grown sample. To study the vibrational modes, the Raman spectra were recorded, which exhibited the expected four Raman active modes. The resistance vs temperature measurement showed a well-established superconducting transition (T_c) at 7.3 K. The ZFC (zero-field cooled) and FC (field cooled) magnetization curves, as well as the isothermal M−H (magnetization vs field) measurements, have been performed for both in-plane and out-of-plane H directions. Distinct anisotropy is observed in both magnetization and magneto-transport measurements with field direction, leading to different critical fields (H_c). Out-of-plane magneto-transport data hints towards the existence of a filamentary state. The density functional theory (DFT) has been used to study the band structure of NbSe₂. Although the bulk band structure confirmed metallic behavior, the same of mono-layers of NbSe₂ within the GGA+U framework showed a band gap of 1.17 eV. The article addresses the anisotropy in the electronic and magneto-transport of 2D superconductor NbSe₂.

Minimization or tailoring of magnetic anisotropies in the order of magneto-crystal, magneto-elastic and external field-induced anisotropies are effective way of improving soft-magnetism in nanocrystalline alloys. The recently developed Fe-rich nanocrystalline alloys have been found to exhibit positive magnetostriction behaviour and magnetic coercivity twice that of FINEMET alloys, after optimal annealing. This makes uniaxial tensile-stress annealing a promising method to improve the soft-magnetism of these alloys. In that direction, the present study investigates the influence of tensile stress annealing on structure, soft-magnetic, magnetostriction and core-loss properties of Fe-rich Fe₈₃Si₂B₉P₄Nb₁Cu₁ nanocrystalline ribbons. The samples were uniformly annealed at 480 °C for 4 min with varying uniaxial tensile stress ranging from 0 to 180 MPa. The XRD results showed that all annealed ribbons had a uniform nanocrystalline microstructure consisting of a BCC α-Fe(Si) phase with an average grain size of less than 20 nm, irrespective of the applied stress. However, the magnetic properties were highly sensitive to the magnitude of the tensile stress during nanocrystallization annealing. The optimal tensile stress ranging from 90-140 MPa resulted in the best combination of soft-magnetic properties (11–12 A/m) and high squareness ratio (0.8-0.9). These ribbons also depicted longitudinal anisotropy (K_u ≤ 0). On the other hand, tensile stress above 165 MPa resulted in the deterioration of magnetic properties (> 24 A/m) and transverse anisotropy behaviour (K_u > 0). The transformation of tensile stress-induced anisotropy from longitudinal to transverse was characterized by the reduction of the magnetostriction constant and change in the magnetization process. The core-loss plots (50-1000 Hz) showed a reduction for optimal stress-annealed (90-140 MPa) ribbons and a drastic increase for 165-180 MPa ribbons. The study highlights the beneficial role of controlled tensile stress annealing in improving the soft-magnetism of Fe-rich nanocrystalline alloys with positive magnetostriction.

Barium hexaferrite (BaFe₁₂O₁₉) and Ni–Zn ferrite (Ni_0.6Zn_0.4Fe₂O₄) powders were synthesized using the microwave hydrothermal method. Composite samples with varying ratios {x(Ni_0.6Zn_0.4Fe₂O₄) + (1 − x) (BaFe₁₂O₁₉)} (where x ranged from 0 to 1.0) were prepared through mechanical mixing. The pure and composite samples were subjected to a 4-h heat treatment at 800 °C. The structural characteristics of the pure samples were analyzed using X-ray diffraction (XRD), revealing the hexagonal structure of BaFe₁₂O₁₉ and the spinel structure of Ni_0.6Zn_0.4Fe₂O₄. Morphological properties were investigated using field emission scanning electron microscopy (FESEM). The results confirmed a hexagonal morphology for BaFe₁₂O₁₉, a spherical morphology for Ni_0.6Zn_0.4Fe₂O₄, and a mixed morphology for the composites, with grain sizes ranging from 50 to 200 nm. The optical properties were explored through UV–Vis absorption studies, and the optical energy gap values were determined using the Tauc plots. The magnetic behavior of the samples was studied by analyzing magnetic hysteresis loops. Pure samples exhibited a smooth hysteresis behavior, while composite samples displayed a step-like pattern. A possible relation between the magnetic interaction between the two different materials in the composites was investigated.