Search

Extended layered oxyhalide compounds, Sr2NiO3X (X = F, Cl), with the square pyramidal coordination around the trivalent nickel ions in the low spin state (S = 1/2), are successfully synthesized by a high-pressure and high-temperature reaction. Both these compounds crystallize in the n = 1 Ruddlesden-Popper type structure, but the difference of halogen anions incorporated dictate the anion-site ordering patterns and the magnetic ground states. Sr2NiO3F adopts the tetragonal cell in the space group I4/mmm (a = b = 3.79125(2) Å and c = 13.13754(9) Å), with O/F anions being disordered at the apical sites, while the crystal structure of Sr2NiO3Cl is described in the tetragonal space group P4/nmm (a = b = 3.85566(1) Å and c = 14.43240(6) Å) with O/Cl anions being fully ordered at the apical sites. Additionally, Sr2NiO3Cl undergoes a long-range antiferromagnetic order below TN = 33 K, while the fluorine counterpart does not exhibit a long-range ordering but spin glass transition at TSG = 11 K. In light of the positive Weiss temperatures for both X = F and Cl, the unpaired electron likely occupies a d(xy) orbital. Namely, the superexchange interaction mediated by d(xy)-OpΠ-d(xy) in the NiO2 basal plane is antiferromagnetic, while the direct exchange interaction between d(xy)-d(xy) along the diagonal directions is ferromagnetic. The origin of spin glass behavior observed in X = F is probably due to randomness of the direct d(xy)-d(xy) bonds caused by off-centering nickel ions and O/F site disordering. [ABSTRACT FROM AUTHOR]

The crystal structure of the cubic double-perovskite Sr2Cr0.84Ni0.09Os1.07O6, grown at high pressure, was solved using intensity data measured at 113 K. The Os site was modelled with a partial Ni occupancy, and the Cr site was modelled with both Os and Ni partial occupancy. The refined structure shows that this cubic form is stable at 113 K. [ABSTRACT FROM AUTHOR]

A high-pressure-synthesized double perovskite Sr2YOsO6 was investigated by synchrotron X-ray diffraction and measurements of its magnetic susceptibility, specific heat capacity, complex impedance, and complex dielectric constant. It crystallized into a monoclinic double perovskite structure (P21/n) with complete ordering of the Y and Os atoms. Its magnetic behaviors, including the antiferromagnetic transition temperature (~52 K), Curie-Weiss effective moment [3.48(5) μB/Os], and Weiss temperature [-350.1(7) K], were close to the respective values of Sr2YOsO6 previously synthesized without an applied pressure of 6 GPa. Transport property measurements revealed that the lower limit of the activation energy was 192(1) meV and the charge gap remained open regardless of the presence of magnetic order, conflicting with the electron delocalization predicted by theoretical calculations. Further consideration, including theoretical and experimental investigations of the roles of spin-orbit coupling and U of the 5d electrons of Os 5d-t2g³, may assist in understanding the general magnetic and insulating behaviors of quasi-half-filled 5d-t2g 3oxides in the perovskite category toward the use of 5d double perovskite for magnetic applications. [ABSTRACT FROM AUTHOR]

The (1 − x)BiFeO3−xLaFeO3system has been investigated and characterized by room-temperature and high-temperature laboratory and synchrotron powder X-ray diffraction, electron diffraction, high-resolution transmission electron microscopy, differential scanning calorimetry, and magnetization measurements. At room temperature, the ferroelectric R3cphase is observed for 0.0 ≤ x≤ 0.10. The PbZrO3-related √2ap× 2√2ap× 4apsuperstructure (where apis the parameter of the cubic perovskite subcell) is observed for Bi0.82La0.18FeO3, while an incommensurately modulated phase is formed for 0.19 ≤ x≤ 0.30 with the √2ap× 2ap× √2apbasic unit cell. The GdFeO3-type phase with space group Pnma(√2ap× 2ap× √2ap) is stable at 0.50 ≤ x≤ 1. Bi0.82La0.18FeO3has no detectable homogeneity range (space group Pnam, a= 5.6004(1) Å, b= 11.2493(3) Å, c= 15.6179(3) Å). The incommensurately modulated Bi0.75La0.25FeO3structure was solved from synchrotron X-ray powder diffraction data (Imma(00γ)s00 superspace group, a= 5.5956(1) Å, b= 7.8171(1) Å, c= 5.62055(8) Å, q= 0.4855(4)c*, RP= 0.023, RwP= 0.033). In this structure, cooperative displacements of the Bi and O atoms occur, which order within the (AO) (where A = Bi, La) layers, resulting in an antipolar structure. Local fluctuations of the intralayer antipolar ordering are compensated by an interaction with the neighboring (AO) layers. A coupling of the antipolar displacements with the cooperative tilting distortion of the perovskite octahedral framework is proposed as the origin of the incommensurability. All the phases transform to the GdFeO3-type structure at high temperatures. Bi0.82La0.18FeO3shows an intermediate PbZrO3-type phase with √2ap× 2√2ap× 2ap(space group Pbam; a= 5.6154(2) Å, b= 11.2710(4) Å, and c= 7.8248(2) Å at 570 K). The compounds in the compositional range of 0.18 ≤ x≤ 0.95 are canted antiferromagnets. [ABSTRACT FROM AUTHOR]

Substitution of Sb with Sn was achieved in ferrimagnetic antiperovskite Mn3SbN. The experimental results indicate that with an increase in Sn concentration, the magnetization continuously decreases and the crystal structure of Mn3Sb1-xSnxN changes from tetragonal to cubic phase at around x of 0.8. In the doping series, step-like anomaly in the isothermal magnetization was found and this behavior was highlighted at x = 0.4. The anomaly could be attributed to the magnetic frustration, resulting from competition between the multiple spin configurations in the antiperovskite lattice. Meantime, Hc of 18 kOe was observed at x=03, which is probably the highest among those of manganese antiperovskite materials reported so far. With increasing Sn content, the abrupt change of resistivity and the sharp peak of heat capacity in Mn3SbN were gradually weakened. The crystal structure refinements indicate the weakened change at the magnetic transition is close related to the change of c/a ratio variation from tetragonal to cubic with Sn content. The results derived from this study indicate that the behavior of Mn3Sb1-xSnxN could potentially enhance its scientific and technical applications, such as spin torque transfer and hard magnets. [ABSTRACT FROM AUTHOR]

We have successfully synthesized Sr2MnO3F, a new layered perovskite oxyfluoride with a n = 1 Ruddlesden-Popper-type structure using a high-pressure, high-temperature method. Structural refinements against synchrotron X-ray diffraction data collected from manganese oxyfluoride demonstrated that it crystallizes in a tetragonal cell with the space group I4/mmm, in which the Mn cation is located at the octahedral center position. This is in stark contrast to the related oxyhalides that have square-pyramidal coordination such as Sr2MO3X (M = Fe, Co, Ni; X = F, Cl) and Sr2MnO3Cl. There was no evidence of O/F site order, but close inspection of the anion environment centered at the Mn cation on the basis of bond-valence-sum calculation suggested preferential occupation of the apical sites by the F ion with one oxide ion in a random manner. Magnetic susceptibility and heat capacity measurements revealed an antiferromagnetic ordering at 133 K (=TN), which is much higher than that of the chloride analogue with corrugated MnO2 planes (TN = 80 K). [ABSTRACT FROM AUTHOR]

We investigated the upper critical fields of Ca10(Pt4As8)(Fe1.8Pt0.2As2)5 superconducting whiskers. The whiskers consist of several wire-like grains with diameter of around 200 nm, joined by grain boundaries whose misorientation angles are less than 5°. The upper critical fields along c-axis and in ab-plane were observed as 49 T at 12K and 50 T at 22K, respectively, which can be extrapolated to 81 and ~133 T at 0 K. The whisker demonstrated weak anisotropic factor and almost constant value of ~2 below 15 K. The impressive transport properties of the whisker may find applications in fields like superconducting micro- and meso-structure systems. [ABSTRACT FROM AUTHOR]

We investigated the upper critical fields of Ca10(Pt4As8)(Fe2-xPtxAs2)5 superconducting whiskers. The whiskers consist of several wire-like grains with diameter of around 200 nm, joined by grain boundaries whose misorientation angles are less than 5°. The upper critical fields along c-axis and in ab-plane were observed as 49 T at 12 K and 50 T at 22 K, respectively, which can be extrapolated to ~81 and ~133 T at 0 K. The whisker demonstrated weak anisotropic factor and almost constant value of ~2 below 15 K. The impressive transport properties of the whisker may find applications in fields like superconducting micro- and meso-structure systems. [ABSTRACT FROM AUTHOR]

Double-perovskite oxides Ca2MgOsO6 and Sr2MgOsO6 have been synthesized under high-pressure and high-temperature conditions (6 GPa and 1500 °C). Their crystal structures and magnetic properties were studied by a synchrotron X-ray diffraction experiment and by magnetic susceptibility, specific heat, isothermal magnetization, and electrical resistivity measurements. Ca2MgOsO6 and Sr2MgOsO6 crystallized in monoclinic (P21/n) and tetragonal (I4/m) double-perovskite structures, respectively; the degree of order of the Os and Mg arrangement was 96% or higher. Although Ca2MgOsO6 and Sr2MgOsO6 are isoelectric, a magnetic-glass transition was observed for Ca2MgOsO6 at 19 K, while Sr2MgOsO6 showed an antiferromagnetic transition at 110 K. The antiferromagnetic-transition temperature is the highest in the family. A first-principles density functional approach revealed that Ca2MgOsO6 and Sr2MgOsO6 are likely to be antiferromagnetic Mott insulators in which the band gaps open, with Coulomb correlations of ∼1.8-3.0 eV. These compounds offer a better opportunity for the clarification of the basis of 5d magnetic sublattices, with regard to the possible use of perovskite-related oxides in multifunctional devices. The double-perovskite oxides Ca2MgOsO6 and Sr2MgOsO6 are likely to be Mott insulators with a magnetic-glass (MG) transition at ~19 K and an antiferromagnetic (AFM) transition at ~110 K, respectively. This AFM transition temperature is the highest among double-perovskite oxides containing single magnetic sublattices. Thus, these compounds offer valuable opportunities for studying the magnetic nature of 5d perovskite-related oxides, with regard to their possible use in multifunctional devices. [ABSTRACT FROM AUTHOR]

We determined phase relations in MgCr2O4 at 12-28 GPa and 1000-1600°C using a multi-anvil apparatus. At 12-15 GPa, spinel-type MgCr2O4 (magnesiochromite) first decomposes into a mixture of new Mg2Cr2O5 phase + corundum-type Cr2O3 at 1100-1600°C, but it dissociates first into MgO periclase + corundum-type Cr2O3 at l000°C. At about 17-19 GPa, the mixture of Mg2Cr2O5 phase + corundum-type Cr2O3 transforms to a single MgCr2O4 phase. Structure refinements using synchrotron X-ray powder diffraction data indicated that the high-pressure MgCr2O4 phase has a CaTi2O4-type structure (Cmcm), and that the basic structure of the Mg2Cr2O5 phase is the same as that of recently found modified ludwigite-type Mg2Al2O5 and Fe2Cr2O5 (Pbam). The phase relations in this study may suggest that natural chromitites in the Luobusa ophiolite regarded as the deep-mantle origin were derived from the mantle shallower than the depths corresponding to pressure of 12-15 GPa because of absence of the assemblage of (Mg,Fe)2Cr2O5 + Cr2O3 in the chromitites. [ABSTRACT FROM AUTHOR]

The polycrystalline MO2's (HP-PdF2-type MO2, M = Rh, Os, Pt) with high-pressure PdF2 compounds were successfully synthesized under high-pressure conditions for the first time, to the best of our knowledge. The crystal structures and electromagnetic properties were studied. Previously unreported electronic properties of the polycrystalline HP-PdF2-type RuO2 and IrO2 were also studied. The refined structures clearly indicated that all compounds crystallized into the HP-PdF2-type structure, M4+O2-2, rather than the pyrite-type structure, Mn+(O2)n- (n < 4). The MO2 compounds (M = Ru, Rh, Os, Ir) exhibited metallic conduction, while PtO2 was highly insulating, probably because of the fully occupied t2g band. Neither superconductivity nor a magnetic transition was detected down to a temperature of 2 K, unlike the case of 3d transition metal chalcogenide pyrites. [ABSTRACT FROM AUTHOR]

Controlling the distribution of mixedanions around a metal centeris a long-standing subject in solid state chemistry. We successfullyobtained single crystals of an iron-based layered perovskite compound,Sr2FeO3F, by utilizing a high-pressure and high-temperaturetechnique. The phase prepared at 1300 °C and 3 GPa crystallizedin tetragonal space group P4/nmmwith O/F atoms at the apical sites being ordered. However, a temperatureof 1800 °C and a pressure of 6 GPa resulted in partial O/F sitedisordering. The degree of anion disordering, which was 5%, showedthat the anion-ordered arrangement was quite robust, in sharp contrastto that of Sr2BO3F (B = Co or Ni) with the fullydisordered state. 57Fe Mössbauer spectroscopy measurementsrevealed no large difference in Néel temperatures between thetwo phases, but the phase prepared under the latter condition exhibiteda quasi-continuous distribution of hyperfine fields caused by O/Fsite disordering. We discuss the mechanism of the anion order-to-disordertransition observed in related oxyfluoride perovskites. [ABSTRACT FROM AUTHOR]

A new compositional double perovskite oxide Ba2CuOsO6 was synthesized under high-pressure (6 GPa) and high-temperature (1500 °C) conditions. The polycrystalline Ba2CuOsO6 was characterized by synchrotron X-ray diffraction, thermogravimetric analysis, and magnetic susceptibility, isothermal magnetization, and specific heat measurements. The oxide crystallizes in a double-perovskite structure with an I4/m space group, in which Os(VI) and Cu(II) are ordered in the perovskite B-site. Ba2CuOsO6 is electrically insulating with an activation energy of 0.813(2) eV and shows antiferromagnetic-like characteristics at temperatures of ~55 K and ~70 K. The results of the first-principle calculation suggested that the spin-orbit interaction of Os(VI) plays a substantial role in the insulating state. The Jahn-Teller distortion of CuO6 octahedra influences the magnetic characteristics with regard to possible two-dimensional magnetic correlations. [ABSTRACT FROM AUTHOR]

We investigated the depairing current density of Ba0.5K0.5Fe1.95Co0.05As2 microbridges with width of 2μm and thickness of 150nm. The current vs. voltage characteristics of the microbridges show a Josephson-like behavior with the obvious hysteresis. The critical current density was observed as Jc=7.9MA/cm² at temperature 21K, which is consistent with the Ginzburg-Landau depairing limit. However, the depairing current density is less than that of impurity-free crystal, although the Co ions provide additional pinning centers within the superconducting Fe2As2 layers. The Co impurity also enhances the anisotropic factor of the critical current density by 1.3 (1T) or 1.7 (3T). [ABSTRACT FROM AUTHOR]

We investigated the normal-state resistivity ρxx(T) and the Hall effect in Zn- and Co-doped Ba0.5K0.5Fe2As2 single-crystalline microbridges. A crossover temperature T* was observed in the temperature dependency of the longitudinal resistivity ρxx(T), which separates ρxx(T) into temperature-linear and temperature-nonlinear regions. Above T*, the carriers in Ba0.5K0.5Fe2As2 and Co-doped Ba0.5K0.5Fe1.94Co0.06As2 demonstrate electronlike behavior and an anomalous nonlinear magnetic field dependence of the Hall voltage with a sign reversal. By contrast, the Zn-doped Ba0.5K0.5Fe1.94Zn0.06As2behaves like a hole type and the Hall coefficient is independent of the magnetic field. The field-induced sign reversal of the Hall coefficient of undoped and Co-doped samples depends on the field modification on the mobility and hole/electron concentration ratio. The T2-dependent Hall angle of a nonmagnetic Zn-doped crystal is observed as a nearly parallel shift from that of the impurity-free crystal in the low-temperature region, indicating that the Zn induces a weak change of the spinons excitations, while increasing the number of scattering centers. The Co works as a nonmagnetic impurity as well, while it provides both spinons excitations and impurity scattering. [ABSTRACT FROM AUTHOR]

Single crystals of YbOs2Al10 and LuOs2Al10 were grown for the first time using an aluminum self-flux method. The compounds crystallized into a cagelike structure in space group Cmcm, similar to the prototype compound YbFe2Al10. YbOs2All0 exhibited a mixed-valent nature, as determined by magnetic susceptibility measurements over a wide temperature range from 2 to 900 K, in which the inter-configuration--fluctuation model revealed a broad peak around 400 K. In contrast, LuOs2Al10 displayed Pauli-like paramagnetic behavior over the same temperature range. Both compounds were metallic in nature between 2 and 300 K. The electronic specific heat coefficient of 21.3(2) mJ mol-l K-2 for YbOs2Al10 was determined to be larger than that for LuOs2Al10 [8.9(1) mJ mol-1 K-2], reflecting the mixed-valent nature of the former. First-principles calculations predicted the presence of a mixed-valent state in YbOs2Al10, in agreement with the experimental observations. The novel compound YbOs2Al10 elucidates the evolution of the mixed-valent nature of the Yb-based ternary transition metal aluminides from the 3d to 5d elements. [ABSTRACT FROM AUTHOR]

5d and 3d hybrid solid-state oxide Ca2FeOsO6 crystallizes into an ordered double-perovskite structure with a space group of P21/n with high-pressures and temperatures. Ca2FeOsO6 presents a long-range ferrimagnetic transition at a temperature of 320 K (Tc) and is not a band insulator, but is electrically insulating like the recently discovered Sr2CrOsO6 (Tc 725 K). The electronic stat of Ca2FeOsO6 is adjacent to a half-metallic state as well as that of Sr2CrOsO6. In addition, the high-Tc ferrimagnetism was driven by lattice distortion, which was observed for the first time among double-perovskite oxides and represents complex interplays between spins and orbitals. Unlike conventional ferrite and garnet, the interplays likely play a pivotal role of the ferrimagnetism. A new class of 5d-3d hybrid ferrimagnetic insulators with high-Tc is established to develop practically and scientifically useful spintronic materials. [ABSTRACT FROM AUTHOR]

In continuation of the series of perovskite oxides that includes 3d4 cubic BaFeO3 and 4d4 cubic BaRuO3, 5d4 cubic BaOsO3 was synthesized by a solid-state reaction at a pressure of 17 GPa, and its crystal structure was investigated by synchrotron powder X-ray diffraction measurements. In addition, its magnetic susceptibility, electrical resistivity, and specific heat were measured over temperatures ranging from 2 to 400 K. The results establish a series of d4 cubic perovskite oxides, which can help in the mapping of the itinerant ferromagnetism that is free from any complication from local lattice distortions for transitions from the 3d orbital to the 5d orbital. Such a perovskite series has never been synthesized at any d configuration to date. Although cubic BaOsO3 did not exhibit long-range ferromagnetic order unlike cubic BaFeO3 and BaRuO3, enhanced feature of paramagnetism was detected with weak temperature dependence. Orthorhombic CaOsO3 and SrOsO3 show similar magnetic behaviors. CaOsO3 is not as conducting as SrOsO3 and BaOsO3, presumably due to impact of tilting of octahedra on the width of the t2g band. These results elucidate the evolution of the magnetism of perovskite oxides not only in the 5d system but also in group 8 of the periodic table. [ABSTRACT FROM AUTHOR]

Crystals of the newly synthesized compound Ca3LiOsO6 were grown by a flux method using LiCl and KCl, followed by single-crystal X-ray diffraction (XRD), low-temperature powder XRD, and measurements of ac and dc magnetic susceptibility and specific heat. The data indicate that Ca3LiOsO6 has a fully opened electronic gap with an antiferromagnetic ordered state, consistent with suggestions from the first-principles study. The observed magnetic transition temperature is 117 K, too high to be caused only by a direct spin-spin interaction. It appears that the original superexchange magnetic path Os-O-Os is absent; thus, the extended superexchange path (Os-O)-(O-Os) can be expected to be responsible for the 117 K magnetic order. If this is true, Ca3LiOsO6 would be highly valuable to study the nature of extended superexchange magnetic interactions in solids. [ABSTRACT FROM AUTHOR]

Abstract  High-pressure phase transitions of CaRhO3 perovskite were examined at pressures of 6–27 GPa and temperatures of 1,000–1,930°C, using a multi-anvil apparatus. The results indicate that CaRhO3 perovskite successively transforms to two new high-pressure phases with increasing pressure. Rietveld analysis of powder X-ray diffraction data indicated that, in the two new phases, the phase stable at higher pressure possesses the CaIrO3-type post-perovskite structure (space group Cmcm) with lattice parameters: a = 3.1013(1) Å, b = 9.8555(2) Å, c = 7.2643(1) Å, V m  = 33.43(1) cm3/mol. The Rietveld analysis also indicated that CaRhO3 perovskite has the GdFeO3-type structure (space group Pnma) with lattice parameters: a = 5.5631(1) Å, b = 7.6308(1) Å, c = 5.3267(1) Å, V m  = 34.04(1) cm3/mol. The third phase stable in the intermediate P, T conditions between perovskite and post-perovskite has monoclinic symmetry with the cell parameters: a = 12.490(3) Å, b = 3.1233(3) Å, c = 8.8630(7) Å, β = 103.96(1)°, V m  = 33.66(1) cm3/mol (Z = 6). Molar volume changes from perovskite to the intermediate phase and from the intermediate phase to post-perovskite are –1.1 and –0.7%, respectively. The equilibrium phase relations determined indicate that the boundary slopes are large positive values: 29 ± 2 MPa/K for the perovskite—intermediate phase transition and 62 ± 6 MPa/K for the intermediate phase—post-perovskite transition. The structural features of the CaRhO3 intermediate phase suggest that the phase has edge-sharing RhO6 octahedra and may have an intermediate structure between perovskite and post-perovskite. [ABSTRACT FROM AUTHOR]

Single crystals of EuMnSb2 were successfully grown and their structural and electronic properties were investigated systematically. The material crystallizes in an orthorhombic-layered structure (space group: Pnma, No. 62) comprising a periodic sequence of -MnSb/Eu/Sb/Eu/- layers (~1nm in thickness), and massless fermions are expected to emerge in the Sb layer, by analogy of the candidate Dirac materials EuMnBi2 and AMnPn2 (A=Ca or Sr or Ba, Pn=Sb or Bi). The magnetic and specific heat measurements of EuMnSb2 suggest an antiferromagnetic ordering of Eu moments near 20 K. A characteristic hump appears in the temperature-dependent electrical resistivity curve at ~25K. A spin-flop transition of Eu moments with an onset magnetic field of ~15kOe (at 2 K) was observed. Interestingly, EuMnSb2 shows a negative magnetoresistance (up to -95%) in contrast to the positive magnetoresistances observed for EuMnBi2 and AMnPn2 (A=Ca or Sr or Ba, Pn=Sb or Bi), providing a unique opportunity to study the correlation between electronic and magnetic properties in this class of materials. [ABSTRACT FROM AUTHOR]

The ferromagnetic semiconductor Ba2 NiOs O6 (Tmag ~ 100 K) was synthesized at 6 GPa and 1500 °C. It crystallizes into a double perovskite structure [Fm-3m; a = 8.0428 (1) Å], where the Ni2+ and Os6+ ions are perfectly ordered at the perovskite B site. We show that the spin-orbit coupling of Os6+ plays an essential role in opening the charge gap. The magnetic state was investigated by density functional theory calculations and powder neutron diffraction. The latter revealed a collinear ferromagnetic order in a > 21 kOe magnetic field at 5 K. The ferromagnetic gapped state is fundamentally different from that of known dilute magnetic semiconductors such as (Ga,Mn)As and (Cd,Mn)Te (Tmag < 180 K), the spin-gapless semiconductor Mn2 CoAl (Tmag ~ 720 K), and the ferromagnetic insulators EuO (Tmag ~ 70 K) and Bi3 Cr3 O11 (Tmag ~ 220 K). It is also qualitatively different from known ferrimagnetic insulators and semiconductors, which are characterized by an antiparallel spin arrangement. Our finding of the ferromagnetic semiconductivity of Ba2 NiOs O6 should increase interest in the platinum group oxides, because this alternative class of materials should be useful in the development of spintronic, quantum magnetic, and related devices. [ABSTRACT FROM AUTHOR]

We review the progress of nonmagnetic impurity doping studies on Fe-based superconductors. On the theoretical side, two highly promising candidates for the pairing symmetry order parameter, i.e. the multi-gap s++ and s± wave models, have been proposed but continuously debated. The debate arises because of the complex gap structure and exceptional magnetic and metallic behaviors of Fe-based superconductors, which may vary the influence of nonmagnetic defects in the chemical potential, impurity disorder, inter- and intra-band scattering strength, and electron localization. This creates difficulties in directly obtaining the most important information for understanding the symmetry order parameter. Experimentally, nonmagnetic impurity substitution studies have been widely carried out, which have provided very useful insights. We review herein the various nonmagnetic impurity doping experiments, including the controlled defects within the superconducting Fe2X2 planes through sample quality improvement, single impurity effects on the electronic state and local moment, the magnetic response of the Fe2X2 planes both on the macroscopic scale as the antiferromagnetic state and the local scale of moment, as well as the significant effect of modifying the transport properties. The experiments enable us to qualitatively analyze the nonmagnetic impurity effects on the superconducting state for many Fe-based superconductors. We also propose herein some strategies for nonmagnetic impurity doping study. As an important model for explaining the nonmagnetic impurity doping effects, the pair-breaking model is compared with various theoretical approaches via analysis of the pair-breaking rates of various Fe-superconductors. [ABSTRACT FROM AUTHOR]

Model calculations indicate that the magnetic skyrmion lattice (SkL) is represented by a superposition of three spin helices at an angle of 120° to each other, the so-called triple-Q state. Using Lorentz transmission electron microscopy, we investigated the relationship between the SkL and the helix in FeGe thin films. After the magnetic field is removed, the ordered skyrmions are trapped inside helimagnetic domain walls (HDWs) where the different helical Q vectors are encountered. In situ observation revealed an unexpected topological excitation under such a zero-field state: skyrmions are spontaneously formed at HDWs. [ABSTRACT FROM AUTHOR]