Magnetic excitations and magnetic structure of EuRbFe4As4 were investigated by inelastic neutron scattering (INS), neutron diffraction, and random phase approximation (RPA) calculations. Below the superconducting transition temperature Tc = 36.5 K, the INS spectra exhibit the neutron spin resonances at Qres = 1.27(2)Å −1 and 1.79(3)Å −1 . They correspond to the Q = (0.5, 0.5, 1) and (0.5, 0.5, 3) nesting wave vectors, showing three dimensional nature of the band structure. The characteristic energy of the neutron spin resonance is Eres = 17.7(3) meV corresponding to 5.7(1)kBTc. Observation of the neutron spin resonance mode and our RPA calculations in conjunction with the recent optical conductivity measurements are indicative of the s± superconducting pairing symmetry in EuRbFe4As4. In addition to the neutron spin resonance mode, upon decreasing temperature below the magnetic transition temperature TN = 15 K, the spin wave excitation originating in the long-range magnetic order of the Eu sublattice was observed in the low-energy inelastic channel. Single-crystal neutron diffraction measurements demonstrate that the magnetic propagation vector of the Eu sublattice is k = (0, 0, 0.25), representing the three-dimensional antiferromagnetic order. Linear spin wave calculations assuming the obtained magnetic structure with the intra-and interplane nearest neighbor exchange couplings of J1/kB = −1.31 K and Jc/kB = 0.08 K can reproduce quantitatively the observed spin wave excitation. Our results show that superconductivity and longrange magnetic order of Eu coexist in EuRbFe4As4 whereas the coupling between them is rather weak.
The possibility of producing polymer-bonded magnets with the aid of additive processes, such as 3D printing, opens up a multitude of new areas of application. Almost any structures and prototypes can be produced costeffectively in small quantities. Extending the 3D printing process allows the manufacturing of anisotropic magnetic structures by aligning the magnetic easy axis of ferromagnetic particles inside a paste-like compound material along an external magnetic field. This is achieved by two different approaches: First, the magnetic field for aligning the particles is provided by a permanent magnet. Secondly, the 3D printing process itselfs generates an anisotropic behavior of the structures. An inexpensive and customizable end-user fused filament fabrication 3D printer is used to print the magnetic samples. The magnetical properties of different magnetic anisotropic Sr ferrite and SmFeN materials are investigated and discussed.
A sharp peak was observed in the doping dependence of the critical current density, J
c, in potassium doped Ba122 single crystals. This behavior is in contrast to the doping dependence of the transition temperature, T
c, which varies much more smoothly around its maximum. We performed fast neutron irradiation on the crystals in order to find out whether the J
c peak results from intrinsic properties or the particular defect landscape. Fast neutrons are known to introduce defects up to a size of a few nanometers, which have proven to be more efficient for flux pinning than the crystallographic defects in the pristine crystals. We find that the peak in J
c shifts to higher doping levels after the irradiation, broadens, and roughly follows the shape of the T
c curve. Moreover, a power law between J
c and T
c is observed in the irradiated crystals, which can be explained by relations between fundamental parameters and T
c observed previously in iron-based superconductors. This power law does not hold for the pristine crystals which indicates that the doping dependence of J
c results from an enhanced pinning efficiency in the under-doped area of the phase diagram.
The vertebrate inner ear contains vestibular receptors with dense crystals of calcium carbonate, the otoconia. The production and maintenance of otoconia is a delicate process, the perturbation of which can lead to severe vestibular dysfunction in humans. The details of these processes are not well understood. Here, we report the discovery of a new otoconial mass in the lagena of adult pigeons that was present in more than 70% of birds. Based on histological, tomographic and elemental analyses, we conclude that the structure likely represents an ectopically-formed otoconial assembly. Given its frequent natural occurrence, we suggest that the pigeon lagena is a valuable model system for investigating misregulated otoconial formation..
Magnetic superconductors are specific materials exhibiting two antagonistic phenomena, superconductivity and magnetism, whose mutual interaction induces various emergent phenomena, such as the reentrant superconducting transition associated with the suppression of superconductivity around the magnetic transition temperature (Tm), highlighting the impact of magnetism on superconductivity. In this study, we report the experimental observation of the ferromagnetic order induced by superconducting vortices in the high-critical-temperature (high-Tc) magnetic superconductor EuRbFe4As4. Although the ground state of the Eu2+ moments in EuRbFe4As4 is helimagnetism below Tm, neutron diffraction and magnetization experiments show a ferromagnetic hysteresis of the Eu2+ spin alignment. We demonstrate that the direction of the Eu2+ moments is dominated by the distribution of pinned vortices based on the critical state model. Moreover, we demonstrate the manipulation of spin texture by controlling the direction of superconducting vortices, which can help realize spin manipulation devices using magnetic superconductors.
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