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Synthesis, magnetic, and theoretical studies of a new family of mononuclear lanthanide complexes exhibiting the very rare cubic coordination geometry.
To identify the genesis of the differing magnetic behaviors for the ferro- (FO) and metamagnetic (MM) polymorphs of [FeCp* 2 ][TCNQ] the low temperature structures of each polymorph were determined from high-resolution synchrotron powder diffraction data.
We report the synthesis, crystal structures, photophysical and magnetic properties of 11 novel lanthanide complexes with the asymmetrically functionalized trispyrazolylborate ligand 4-nitrotrispyrazolylborate, 4-NO 2 Tp–: [Ln(4-NO 2 Tp) 3 ] (Ln = La–Dy, except Pm). In-depth photophysical characterization of the ligands via luminescence, reflectance and absorption spectroscopic techniques, decay lifetimes, quantum yields supported by time-dependent density functional theory (TD-DFT) and natural bond order (NBO) analysis reveal that n-NO 2 Tp– ligands are dominated by intra-ligand charge transfer (ILCT) transitions and that second-sphere interactions are critical to the stabilization of the T 1 state of n-NO 2 Tp– ligands and hence their ability to sensitize Ln 3+ emission. The luminescence properties of the complexes indicate that 4-NO 2 Tp– is a poor sensitizer of Ln 3+ emission, unlike 3-NO 2 Tp–. Moreover, [Nd(4-NO 2 Tp) 3 ] (crystallized as a hexane solvate) displays single-molecule magnet (SMM) properties, with longer relaxation times and larger barrier than the non-functionalized [NdTp 3 ], attributed to the addition of the NO 2 -group and subsequent rigidification of the molecular structure.
Bimodal particles of NdFeB and SmFeB yielded high-density bonded magnets. The energy product of 20 MGOe with 81 vol% magnet loading was demonstrated.
In the self-magnetic-pinch diode, the electron beam, produced through explosive field emission, focuses on the anode surface due to its own magnetic field. This process results in dense plasma formation on the anode surface, consisting primarily of hydrocarbons. Direct measurements of the beam’s current profile are necessary in order to understand the pinch dynamics and to determine x-ray source sizes, which should be minimized in radiographic applications. In this paper, the analysis of the C IV doublet (580.1 and 581.2 nm) line shapes will be discussed. The technique yields estimates of the electron density and electron temperature profiles, and the method can be highly beneficial in providing the current density distribution in such diodes.
The 2 + 1 SU(3) Polyakov linear sigma model (PLSM) is used to investigate the respective influence of a finite volume and a magnetic field on the quark-hadron phase boundary in the plane of baryon chemical potential (μ B ) vs. temperature (T) of the QCD phase diagram. The calculated results indicate sizable shifts of the quark-hadron phase boundary to lower values of (μ B and T) for increasing magnetic field strength, and an opposite shift to higher values of (μ B and T) for decreasing system volume. Such shifts could have important implications for extraction of the thermodynamic properties of the QCD phase diagram from heavy ion data.
In fixed-boundary axisymmetric equilibrium calculations the plasma shape is assigned from input. In several circumstances, the plasma shape may not be known a priori, or one may desire to also compute the magnetic field in the volume surrounding the plasma through the calculation of a free-boundary equilibrium. This requires either the coil currents or the magnetic poloidal flux on a curve in the vacuum region to be assigned as input for the free-boundary equilibrium calculation. The FREE-FIX code presented in this article is a general tool for calculating coil currents being given a fixed-boundary calculation. Finally, a new formulation is presented, which considerably reduces the computational cost of the calculation. FREE-FIX performs well for different geometries and experiments.
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The debate concerning whether the insulating phases of vanadium dioxide (VO 2 ) can be described by band theory or whether it requires a theory of strong electron correlations remains unresolved even after decades of research. Energy-band calculations using hybrid exchange functionals or including self-energy corrections account for the insulating or metallic nature of different phases but have not yet successfully accounted for the observed magnetic orderings. Strongly correlated theories have had limited quantitative success. Here we illustrate that by using hard pseudopotentials and an optimized hybrid exchange functional, the energy gaps and magnetic orderings of both monoclinic VO 2 phases and the metallic nature of the high-temperature rutile phase are consistent with available experimental data, obviating an explicit role for strong correlations. We also identify a potential candidate for the newly found metallic monoclinic phase.
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The strong interplay of fundamental order parameters in complex oxides is known to give rise to exotic physical phenomena. The 4$d$ transition-metal oxide SrRh O 3 has generated much interest, but advances have been hindered by difficulties in preparing single-crystalline phases. Here we epitaxially stabilize high-quality single-crystalline SrRh O 3 films and investigate their structural, electronic, and magnetic properties. Lastly, we determine that their properties significantly differ from the paramagnetic metallic ground state that governs bulk samples and are strongly related to rotations of Rh O 6 octahedra.
Here, we present a thorough study of doping dependent magnetic hysteresis and relaxation characteristics in single crystals of (Ba 1-x K x ) Fe 2 As 2 (0.18 ≤ x ≤ 1). The critical current density J c reaches maximum in the underdoped sample x = 0.26 and then decreases in the optimally doped and overdoped samples. Meanwhile, the magnetic relaxation rate S rapidly increases and the flux creep activation barrier U 0 sharply decreases in the overdoped sample x = 0.70. These results suggest that vortex pinning is very strong in the underdoped regime, but it is greatly reduced in the optimally doped and overdoped regime. Transmission electron microscope (TEM) measurements reveal the existence of dislocations and inclusions in all three studied samples x = 0.38, 0.46, and 0.65. An investigation of the paramagnetic Meissner effect (PME) suggests that spatial variations in T c become small in the samples x = 0.43 and 0.46, slightly above the optimal doping levels. Our results support that two types of pinning sources dominate the (Ba 1-x K x ) Fe 2 As 2 crystals: (i) strong δl pinning, which results from the fluctuations in the mean free path l and δT c pinning from the spatial variations in T c in the underdoped regime, and (ii) weak δT c pinning in the optimally doped and overdoped regime.
In this work, first-principles calculations based on density functional theory are used to describe the ideal magnetization reversal through polarization switching in BaCuF 4 which, according to our results, could be accomplished close to room temperature. Furthermore, we show that this ideal coupling is driven by a single soft mode that combines both polarization, and octahedral rotation. The later being directly coupled to the weak ferromagnetism of BaCuF 4 . This, added to its strong Jahn-Teller distortion and its orbital ordering, makes this material a very appealing prototype for crystals in the A B X 4 family for multifunctional applications. The described mechanism behaves ideally as it couples the ferroelectric and the magnetic properties naturally and it has not been reported previously.
Optical excitation of stripe-ordered La 2–x Ba x CuO 4 has been shown to transiently enhance superconducting tunneling between the CuO 2 planes. This effect was revealed by a blueshift, or by the appearance of a Josephson plasma resonance in the terahertz-frequency optical properties. Here, we show that this photoinduced state can be strengthened by the application of high external magnetic fields oriented along the c axis. For a 7 T field, we observe up to a tenfold enhancement in the transient interlayer phase correlation length, accompanied by a twofold increase in the relaxation time of the photoinduced state. These observations are highly surprising, since static magnetic fields suppress interlayer Josephson tunneling and stabilize stripe order at equilibrium. We interpret our data as an indication that optically enhanced interlayer coupling in La 2–x Ba x CuO 4 does not originate from a simple optical melting of stripes, as previously hypothesized. Furthermore, we speculate that the photoinduced state may emerge from activated tunneling between optically excited stripes in adjacent planes.
Electron-beams with a sinusoidal energy modulation have the potential to emit sub-femtosecond x-ray pulses in a free-electron laser. The energy modulation can be generated by overlapping a powerful infrared laser with an electron-beam in a magnetic wiggler. Here we report on a new infrared source for this modulation, coherent radiation from the electron-beam itself. In this self-modulation process, the current spike on the tail of the electron-beam radiates coherently at the resonant wavelength of the wiggler, producing a six-period carrier-envelope-phase (CEP) stable infrared field with gigawatt power. This field creates a few MeV, phase-stable modulation in the electron-beam core. The modulated electron-beam is immediately useful for generating sub-femtosecond x-ray pulses at any machine repetition rate, and the CEP-stable infrared field may find application as an experimental pump or timing diagnostic.
Polycrystalline and single-crystal samples of the insulating Shastry-Sutherland compound Er 2 Be 2 SiO 7 were synthesized via a solid-state reaction and the floating zone method, respectively. The crystal structure, Er single-ion anisotropy, zero-field magnetic ground state, and magnetic phase diagrams along high-symmetry crystallographic directions were investigated with bulk measurement techniques, x-ray and neutron diffraction, and neutron spectroscopy. Here, we establish that Er 2 Be 2 SiO 7 crystallizes in a tetragonal space group with planes of orthogonal Er dimers and a strong preference for the Er moments to lie in the local plane perpendicular to each dimer bond. We also find that this system has a noncollinear ordered ground state in zero field with a transition temperature of 0.841 K consisting of antiferromagnetic dimers and in-plane moments. Finally, we mapped out the H-T phase diagrams for Er 2 Be 2 SiO 7 along the directions H ∥ [001], [100], and [110]. While an increasing in-plane field simply induces a phase transition to a field-polarized phase, we identify three metamagnetic transitions in the H ∥ [001] case. Single-crystal neutron diffraction results reveal that the H ∥ [001] phase diagram can be explained predominantly by the expected field-induced behavior of classical, anisotropic moments, although the microscopic origin of one phase requires further investigation.
This work presents the detailed design of an outer rotor motor and integrated drive for passenger electric vehicles. The motor uses non-heavy rare earth permanent magnets and operates at a top speed of 20,000rpm. In-slot ceramic heat exchangers are utilized for the cooling of the windings. The external rotor configuration of the motor leaves a significant amount of space in the stator bore, which is leveraged for the integration of the power electronics. A high speed external rotor motor creates a number of mechanical, thermal and assembly challenges and this work presents detailed thermal, mechanical and rotordynamics analysis.
This paper provides a loss breakdown of the NovaMAX® 215 frame, 1800 rpm motor at 5 kW. Mechanical losses, copper loss, and various types of electromagnetic losses are identified through experiment and simulation. The motor is able to achieve a very high efficiency, up to 96% at some operating points. A comparison with another highly efficient permanent magnet motor illustrates the benefits of the dual rotor axial flux topology, the use of grain oriented electrical steel, and the conical air gap and rotor flux focusing topology together with ferrite magnets. Additionally, a motor with a variable air gap was tested at different air gaps, and its losses are shown. At low speed and high torque, the losses are minimized with relatively small air gaps. However, at higher speeds and lower torques, the optimal air gaps are larger.