Weyl semimetals are crystalline solids that host emergent relativistic Weyl fermions and have characteristic surface Fermi-arcs in their electronic structure. Weyl semimetals with broken time reversal symmetry are difficult to identify unambiguously. In this work, using angle-resolved photoemission spectroscopy, we visualized the electronic structure of the ferromagnetic crystal Co3Sn2S2 and discovered its characteristic surface Fermi-arcs and linear bulk band dispersions across the Weyl points. These results establish Co3Sn2S2 as a magnetic Weyl semimetal that may serve as a platform for realizing phenomena such as chiral magnetic effects, unusually large anomalous Hall effect and quantum anomalous Hall effect.

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We report experimental observation of large anomalous Hall effect exhibited in non-collinear triangular antiferromagnet D019-type Mn3Ga with coplanar spin structure at temperatures higher than 100 K. The value of anomalous Hall resistivity increases with increasing temperature, which reaches 1.25 μΩ · cm at a low field of ~300 Oe at room temperature. The corresponding room-temperature anomalous Hall conductivity is about 17 (Ω · cm)−1. Most interestingly, as temperature falls below 100 K, a temperature-independent topological-like Hall effect was observed. The maximum peak value of topological Hall resistivity is about 0.255 μΩ · cm. The appearance of the topological Hall effect is attributed to the change of spin texture as a result of weak structural distortion from hexagonal to orthorhombic symmetry in Mn3Ga. Present study suggests that Mn3Ga shows promising possibility to be antiferromagnetic spintronics or topological Hall effect-based data storage devices.

We have studied the stress-induced martensitic transformation behaviors and the associated elastocaloric effect (eCE) for non-textured polycrystalline all-d-metal Heusler alloys of Ni50Mn32Ti18 and Ni35Co15Mn35Ti15 by a combination of Digital Image Correlation (DIC) and Infrared (IR) thermography techniques. A large but irreversible adiabatic temperature change (ΔTad) of 10.7 K at a strain level of 3.9% is observed for Ni50Mn32Ti18, whereas Ni35Co15Mn35Ti15 exhibits a reversible eCE with ΔTad = 9.0 K at a strain level of 4.6%. At lower strain levels (<2.4%), both specimens exhibit full superelasticity without residual strain. While in a higher strain range (>3.2%), Ni50Mn32Ti18 is plastically deformed with small strain variation in space from the DIC map. In contrast, Ni35Co15Mn35Ti15 can be deformed superelastically accompanied by large strain variation in space, which can be ascribed predominately to the crystalline orientation dependence of both the transformation strain and the Young's modulus from different orientated grains under mechanical loading. The improved reversibility of eCE for Ni35Co15Mn35Ti15 is supposed to be associated with the enhancement of d-d hybridization by the introduction of the element Co.

Site preference of doped Mn ions in CoCr2−xMnxO4 (x = 0–2) series has been derived separately from structure and magnetic measurement. It shows that parts of the doped Mn ions occupy the A (Co) sites when x < 0.5. And then, it takes the two B (Cr) sites in turn before and after x = 1.3. This site preference behavior results in a role conversion of the magnetic contributors and, thus, leads to the composition dependent magnetic compensation. Temperature induced compensation and negative magnetization have also been found in several samples, which is attributed to the large energy barrier between the ferromagnetic and antiferromagnetic spin arrangement. A structure transition from cubic to tetragonal symmetry has been detected.

We propose new topological insulators in hexagonal wurtzite-type binary compounds based on the first principles calculations. It is found that two compounds AgI and AuI are three-dimensional topological insulators with a naturally opened band-gap at Fermi level. From band inversion mechanism point view, this new family of topological insulators is similar with HgTe, which has s (Γ 6 ) -p (Γ 8 ) band inversion. Our results strongly support that the spin-orbit coupling is not an essential factor to the band inversion mechanism; on the contrary, it is mainly responsible to the formation of a global band gap for the studied topological insulators. We further theoretically explore the feasibility of tuning the topological order of the studied compounds with two types of strains. The results show that the uniaxial strain can contribute extremely drastic impacts to the band inversion behavior, which provide an effective approach to induce topological phase transition.

By using first-principles calculations, we have systematically investigated the phase stability, magnetism and electron-filling behavior of vanadium-based inverse Heusler compounds. Our calculation results indicate that, due to the complex hybridization of the d orbitals for the vanadium atom, the electronic structures of the vanadium-based inverse Heusler compounds show two opened gaps (one locates in the spin-up channel and the other in the spin-down channel) near the Fermi level, originating from different bonding states. Based on the unique electronic structures, we proposed a generalized electron-filling rule, which can qualitatively explain the unusual change of the molecular spin magnetic moment as a function of the total number of valence electrons observed in the vanadium-based inverse Heusler compounds. Moreover, most of the vanadium-based inverse Heusler compounds have a negative formation energy, which indicates that they are promising to be synthesized experimentally.