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Melt-spinning technique can widen the range of Ga content in Eu8GaxGe46−x type-I clathrate. In this paper, it was used to obtain Eu8GaxGe46−x with nominal 16 ≥ x ≥ 10. Three samples with nominal x = 16, 14, and 12 are discussed in detail. Their actual Ga contents detected by EDS are 14.3, 13.4, and 11.5, which is a relatively wide range that has not been reported before. The decrease of Ga content results in the decrease of lattice parameter a. Moreover, a huge decline of the ferromagnetic transition temperature TC is observed. It is 34.7 K, 27.0 K, and 20.0 K for Eu8GaxGe46−x with nominal x =16, 14, and 12, respectively. However, the saturation magnetic moment μsat and effective magnetic moment μeff are not greatly affected by the change of Ga content. The decrease of TC is mainly attributed to the decrease of molecular field coefficient λ, which can be calculated by fitting the relation curve between exchange mean field Hexch and magnetization M. The fitted λ values are 0.25, 0.18, and 0.16 for samples with nominal x = 16, 14, and 12. Because the decrease of TC is beneficial to the increase of magnetic entropy change, the maximum value of magnetic entropy change (-ΔSMmax) around TC when ΔH = 3 T increases from 6.0 to 7.0 J/(kg K) as x decreases from 16 to 12.

Recently, as a novel technique, electronic double-layer transistors (EDLTs) with ionic liquids have shown strong potential for tuning the electronic states of correlated systems. EDLT induced local carrier doping can always lead to dramatic changes in physical properties when compared to parent materials, e.g. insulating-superconducting (SC) transition. Generally, the modification of gate voltage (VG) in EDLT devices produces a direct change on the doping level. Here, we report that the processing temperature (TG) also plays a dominant role in the electric field induced superconductivity in layered ZrNBr single crystals. When applying VG at T G ≥ 250 K, the induced SC state is irreversible in the material, which is confirmed in the zero resistance and diamagnetism after long-time relaxation at room temperature and/or by applying reverse voltage, whereas the solid/liquid interface induced reversible insulating-SC transition occurs at T G ≤ 235 K. These experimental facts support another electrochemical mechanism that electric field induced partial deintercalation of Br ions could cause permanent electron doping into the system. Our findings in this study will extend the potential of electric fields for tuning bulk electronic states in low-dimension systems.

The iron-based nontoxic chalcogenide superconductor Fe(Te,Se) has great potential for high magnetic field applications while it lacks a reliable method to produce bulk superconductor so far. Here we report a one-step synthesis method to grow high-quality Fe(Te,Se) single crystals free of interstitial iron atoms through minor Mn doping. Bulk superconductivity is revealed in the as-grown centimeter-sized crystals with the optimal doping level of 1% Fe atoms substituted by Mn, which is systematically demonstrated by sharp electrical resistivity and magnetic susceptibility transitions, and large specific heat jumps. Compared with the un-doped sample, the optimally doped one shows a significantly enhanced upper critical field, and a large self-field critical current density Jc of 4.5 × 105 A cm−2 at 2 K (calculated by the Bean model), which maintains large values under high fields. The absence of interstitial iron atoms is testified by the scanning tunneling microscopy, and the effect of Mn doping is discussed. Our results provide a practical method by minor Mn doping to directly synthesize high-performance Fe(Te,Se) bulks that allow for future high-field superconducting applications.

The Ruddlesden–Popper (R–P) bilayer nickelate, La 3 Ni 2 O 7 , was recently found to show signatures of high-temperature superconductivity (HTSC) at pressures above 14 GPa (ref.  1 ). Subsequent investigations achieved zero resistance in single-crystalline and polycrystalline samples under hydrostatic pressure conditions 2 – 4 . Yet, obvious diamagnetic signals, the other hallmark of superconductors, are still lacking owing to the filamentary nature with low superconducting volume fraction 2 , 4 , 5 . The presence of a new 1313 polymorph and competing R–P phases obscured proper identification of the phase for HTSC 6 – 9 . Thus, achieving bulk HTSC and identifying the phase at play are the most prominent tasks. Here we address these issues in the praseodymium (Pr)-doped La 2 PrNi 2 O 7 polycrystalline samples. We find that substitutions of Pr for La effectively inhibit the intergrowth of different R–P phases, resulting in a nearly pure bilayer structure. For La 2 PrNi 2 O 7 , pressure-induced orthorhombic to tetragonal structural transition takes place at P c  ≈ 11 GPa, above which HTSC emerges gradually on further compression. The superconducting transition temperatures at 18–20 GPa reach T c onset = 82.5 K and T c zero = 60 K , which are the highest values, to our knowledge, among known nickelate superconductors. Importantly, bulk HTSC was testified by detecting clear diamagnetic signals below about 75 K with appreciable superconducting shielding volume fractions at a pressure of above 15 GPa. Our results not only resolve the existing controversies but also provide directions for exploring bulk HTSC in the bilayer nickelates. Bulk high-temperature superconductivity observed in pressurized tetragonal La 2 PrNi 2 O 7 was testified by detecting clear diamagnetic signals below about 75 K with appreciable superconducting shielding volume fractions at a pressure of above 15 GPa.

Materials with exceptional magnetism and superconductivity usually conceive emergent physical phenomena. Here, we investigate the physical properties of the (Eu,La)FeAs2 system with double magnetic sublattices. The parent EuFeAs2 shows anisotropy-associated magnetic behaviors, such as Eu-related moment canting and exchange bias. Through La doping, the magnetic anisotropy is enhanced with ferromagnetism of Eu2+ realized in the overdoped region, and a special exchange bias of the superposed ferromagnetic/superconducting loop revealed in Eu0.8La0.2FeAs2. Meanwhile, the Fe-related antiferromagnetism shows unusual robustness against La doping. Theoretical calculation and 57Fe Mössbauer spectroscopy investigation reveal a doping-tunable dual itinerant/localized nature of the Fe-related antiferromagnetism. The coexistence of the Eu-related ferromagnetism, Fe-related robust antiferromagnetism, and superconductivity is further revealed in Eu0.8La0.2FeAs2, providing a platform for further exploration of potential applications and emergent physics. Finally, an electronic phase diagram is established for (Eu,La)FeAs2 with the whole superconducting dome adjacent to the Fe-related antiferromagnetic phase, which is of benefit for seeking underlying clues to high-temperature superconductivity.

A series of Co-doped EuFe 2− x Co x As 2 compounds were prepared in both of single crystalline and polycrystalline forms. The Co-doping effects on the crystal structure, electrical resistivity and magnetic susceptibility were systematically studied. Superconductivity was found in polycrystalline Co-doped samples from zero resistivity effects, with the highest onset superconducting transition temperature at 26 K in the optimum doped EuFe 1.84 Co 0.16 As 2 compound. While due to the stronger competition between the superconducting order and the Eu 2+ magnetic order, the zero resistivity effect is absent in the Co-doped single crystal samples.

The discovery of EuFeAs 2 , currently the only charge-neutral parent phase of the 112-type iron-pnictide system, provides a new platform for the study of elemental doping effects on magnetism and superconductivity (SC). In this study, a series of polycrystalline EuFe 1− y Co y As 2 and Eu 0.9 Pr 0.1 Fe 1− y Co y As 2 samples are synthesized through solid-state reaction, and the evolutions of SC and magnetism with Co doping in EuFeAs 2 and Eu 0.9 Pr 0.1 FeAs 2 are investigated by electrical transport and magnetic susceptibility measurements. For EuFe 1− y Co y As 2 , the Eu-related antiferromagnetic (AFM) transition around 40 K is barely affected by Co doping, while the Fe-related spin density wave (SDW) transition temperature drops rapidly. Meanwhile, SC is induced by a trace amount of Co doping, with a highest transition temperature T c ∼28 K found in EuFe 0.9 Co 0.1 As 2 . For the Eu 0.9 Pr 0.1 Fe 1− y Co y As 2 series, the magnetism and superconductivity show similar evolutions upon Co doping, and the highest T c is enhanced to 30.6 K with an optimum doping level y ∼ 0.07. Our results shed light on the competition between SC and SDW with Co doping in the 112-type EuFeAs 2 system.

The discovery of EuFe[As.sub.2], currently the only charge-neutral parent phase of the 112-type iron-pnictide system, provides a new platform for the study of elemental doping effects on magnetism and superconductivity (SC). In this study, a series of polycrystalline Eu[Fe.sub.1-y][Co.sub.y][As.sub.2] and [Eu.sub.0.9][Pr.sub.0.1][Fe.sub.1-y][Co.sub.y][As.sub.2] samples are synthesized through solid-state reaction, and the evolutions of SC and magnetism with Co doping in EuFe[As.sub.2] and [Eu.sub.0.9][Pr.sub.0.1]Fe[As.sub.2] are investigated by electrical transport and magnetic susceptibility measurements. For Eu[Fe.sub.1-y][Co.sub.y][As.sub.2], the Eu-related antiferromagnetic (AFM) transition around 40 K is barely affected by Co doping, while the Fe-related spin density wave (SDW) transition temperature drops rapidly. Meanwhile, SC is induced by a trace amount of Co doping, with a highest transition temperature [T.sub.c] ~ 28 K found in Eu[Fe.sub.0.9][Co.sub.0.1][As.sub.2]. For the [Eu.sub.0.9][Pr.sub.0.1][Fe.sub.1-y][Co.sub.y][As.sub.2] series, the magnetism and superconductivity show similar evolutions upon Co doping, and the highest [T.sub.c] is enhanced to 30.6 K with an optimum doping level y ~ 0.07. Our results shed light on the competition between SC and SDW with Co doping in the 112-type EuFe[As.sub.2] system. EuFe[As.sub.2], iron-based superconductors, superconductivity, magnetism PACS number(s): 74.70.-b, 74.70.Xa, 74.25.-q, 75.50.Ee