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In this paper, we propose an energy harvester that overcomes the bottleneck problem under ultralow-frequency rotational motion. The harvester consists of bistable dual piezoelectric energy harvesters (BD-PEH) with the magnetic plucking mechanism. The driving magnet is introduced to provide the magnetic plucking to BD-PEH. Therefore, the BD-PEH can operate at high-frequency vibrations across the potential well under ultralow-frequency rotation, which enhances energy harvesting efficiency. A numerical model of the harvester is developed, and the model results are in agreement with the experimental results. The effect of the depth of the potential well on the performance of the harvester is analyzed. The deeper the potential well, the higher the energy output, but it will reduce the bandwidth of the harvester. The experimental results show that the highest average power output is 0.81 mW at 1.2 Hz. In conclusion, the energy harvester proposed in this paper can generate enough energy to drive low-power electronic devices under ultralow-frequency rotational motion. [ABSTRACT FROM AUTHOR]

We report the observation of in-plane anisotropic magnetoresistance (AMR) and planar Hall effect in our recently discovered kagome antiferromagnetic off-stoichiometric single crystal of Mn3Ga. We found that the in-plane AMR is dominated by a sixfold symmetry at low temperature due to the kagome lattice magnetocrystalline anisotropy. However, an unusual fourfold symmetry is also revealed by the angular-dependent AMR measurements, which originates from the little distortion of the crystal accompanying the slight ferromagnetic transition. Moreover, we also found a clear planar Hall effect signal in off-stoichiometric single crystal of Mn3Ga, which may be related to the chiral anomaly, one of the signatures of the magnetic Weyl fermions. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) van der Waals magnetic materials that host skyrmions are promising candidates for the next-generation memory devices. Here, we have predicted a class of 2D chromium-based monolayer ferromagnetic semiconducting materials with a Curie temperature (Tc) exceeding 320 K. We systematically studied their ferromagnetism and quantum transport properties by employing a combination of density functional calculations, Monte Carlo simulations, atomic spin dynamics simulations, and non-equilibrium Green function methods. These materials display topological magnetic spin texture, i.e., magnetic skyrmions, resulting from the competitions between magnetic anisotropy and Dzyaloshinskii–Moriya interaction (DMI). Furthermore, we observed the generation and annihilation of Néel skyrmion lattice and asymmetric bimeron lattice in the magnetic field, which can be controlled by an external magnetic field. By tuning the detailed spin configurations and skyrmion density, we can effectively manipulate the signs and magnitudes of the topological Hall conductance. Our results demonstrate the tunable topology and magnetism of the discovered 2D vdW CrXY3 materials, paving the way for skyrmion-based spintronic devices. [ABSTRACT FROM AUTHOR]

Exciton dynamics in a GaAsSb/GaAs quantum well (QW) heterostructure were investigated via both steady state and transient photoluminescence. The measurements at 10 K demonstrated the coexistence of localized excitons (LEs) and free excitons (FEs), while a blue-shift resulting from increased excitation intensity indicated their spatially indirect transition (IT) characteristics due to the type-II band alignment. With increasing temperature from 10 K, the LEs and FEs redistribute, with the LEs becoming less intense at relatively higher temperature. With increasing temperature to above 80 K, electrons in GaAs are able to overcome the small band offset to enter inside GaAsSb and recombine with holes; thus, a spatially direct transition (DT) appeared. Hence, we are able to reveal complex carrier recombination dynamics for the GaAsSb/GaAs QW heterostructure, in which the "S" shape behavior is generated not only by the carrier localization but also by the transformation from IT to DT with elevated temperature. [ABSTRACT FROM AUTHOR]

Magnetoresistance (MR) and Hall resistivity of TbCo2 and DyCo2 with a Co Kagome lattice were investigated. Apart from giant negative magnetoresistance (MR) at TC, plateau-like MR and a topological Hall effect (THE) are observed at a low magnetic field for each compound below respective TC. The plateau-like MR is attributed to a compensation of negative MR with a ferromagnetically ordered structure of Tb atoms by positive MR with a noncoplanar spin structure of the Co Kagome lattice. The THE is attributed to the noncoplanar spin structure of the Co Kagome lattice only. The MR and the Hall resistivity of each compound are reduced dramatically and undergo a reversal of its sign during cooling. The reversal phenomenon at the low temperature can be related to the freezing of spins of Co atoms. The transport in DyCo2 is more sensitive to magnetic fields than that in TbCo2 which is consistent with a stronger 4f–3d interaction. Observations of these transport phenomena make RCo2 compounds promising for functional applications in spintronic devices. [ABSTRACT FROM AUTHOR]

Magnetoresistance (MR) and Hall resistivity of TbCo2 and DyCo2 with a Co Kagome lattice were investigated. Apart from giant negative magnetoresistance (MR) at TC, plateau-like MR and a topological Hall effect (THE) are observed at a low magnetic field for each compound below respective TC. The plateau-like MR is attributed to a compensation of negative MR with a ferromagnetically ordered structure of Tb atoms by positive MR with a noncoplanar spin structure of the Co Kagome lattice. The THE is attributed to the noncoplanar spin structure of the Co Kagome lattice only. The MR and the Hall resistivity of each compound are reduced dramatically and undergo a reversal of its sign during cooling. The reversal phenomenon at the low temperature can be related to the freezing of spins of Co atoms. The transport in DyCo2 is more sensitive to magnetic fields than that in TbCo2 which is consistent with a stronger 4f–3d interaction. Observations of these transport phenomena make RCo2 compounds promising for functional applications in spintronic devices. [ABSTRACT FROM AUTHOR]

We present a comprehensive study of angular-dependent magnetoresistance (MR) in the layered chiral helimagnet Cr1/3NbS2 (CNS), which realizes a magnetic soliton lattice. It was found that, at temperatures below Curie temperature, CNS showed a negative magnetoresistance related to the emergence of a chiral soliton lattice state when a magnetic field was applied parallel to the ab-plane (H ‖ ab-plane). When the magnetic field was applied parallel to the c-axis (H ‖ c-axis), however, the negative MR disappeared and a positive MR appeared around zero field at low temperatures. Detailed analysis and modeling indicate that the positive MR is due to the weak anti-localization effect arising from the strong spin–orbit coupling of CNS. [ABSTRACT FROM AUTHOR]

The structure, magnetism, and topological transport properties of noncollinear antiferromagnetic hexagonal Mn3Ga magnets have been investigated. Structural analyses reveal that as the temperature decreases, hexagonal Mn3Ga shows a Jahn–Teller-like distortion at T = 120 K. The distortion results in the anisotropy decreasing with decreasing temperature. Positive magnetoresistance is observed, and humps occur at low magnetic fields, which can be understood by breaking the ordered antiferromagnetic configuration by an external field and the spin-dependent scattering mechanism, respectively. In addition, a large topological Hall effect is observed in Mn3Ga, which originates from the noncollinear triangular magnetic configuration with slight distortion. The results are discussed in the context of coupling with noncollinear spin canting, lattice distortion, and topological transport. [ABSTRACT FROM AUTHOR]

We report on the observation of a large topological Hall effect (THE) over a wide temperature region in a geometrically frustrated Fe3Sn2 magnet with a kagome-bilayer structure. We found that the magnitude of the THE resistivity increases with temperature and reaches −0.875 μΩ cm at 380 K. Moreover, the critical magnetic fields with the change of THE are consistent with the magnetic structure transformation, which indicates that the real-space fictitious magnetic field is proportional to the formation of magnetic skyrmions in Fe3Sn2. The results strongly suggest that the large THE originates from the topological magnetic spin textures and may open up further research opportunities in exploring emergent phenomena in kagome materials. [ABSTRACT FROM AUTHOR]

We report on the observation of a large topological Hall effect (THE) over a wide temperature region in a geometrically frustrated Fe3Sn2 magnet with a kagome-bilayer structure. We found that the magnitude of the THE resistivity increases with temperature and reaches −0.875 μΩ cm at 380 K. Moreover, the critical magnetic fields with the change of THE are consistent with the magnetic structure transformation, which indicates that the real-space fictitious magnetic field is proportional to the formation of magnetic skyrmions in Fe3Sn2. The results strongly suggest that the large THE originates from the topological magnetic spin textures and may open up further research opportunities in exploring emergent phenomena in kagome materials. [ABSTRACT FROM AUTHOR]