More Like this

1. Large anomalous Hall effect and negative magnetoresistance in half-topological semimetals

   https://doi.org/10.1038/s42005-023-01469-6  

   Zhu, Yanglin; Huang, Cheng-Yi; Wang, Yu; Graf, David; Lin, Hsin; Lee, Seng Huat; Singleton, John; Min, Lujin; Palmstrom, Johanna C.; Bansil, Arun; et al (December 2023, Communications Physics)

   Proposed mechanisms for large intrinsic anomalous Hall effect (AHE) in magnetic topological semimetals include diverging Berry curvatures of Weyl nodes, anticrossing nodal rings or points of non-trivial bands. Here we demonstrate that a half-topological semimetal (HTS) state near a topological critical point can provide an alternative mechanism for a large AHE via systematic studies on an antiferromagnetic (AFM) half-Heusler compound TbPdBi. We not only observe a large AHE with tanΘ^H≈ 2 in its field-driven ferromagnetic (FM) phase, but also find a distinct Hall resistivity peak in its canted AFM phase. Moreover, we observe a large negative magnetoresistance with a value of ~98%. Our in-depth theoretical modelling indicates that these exotic transport properties originate from the HTS state which exhibits Berry curvature cancellation between the trivial spin-up and nontrivial spin-down bands. Our study offers alternative strategies for improved materials design for spintronics and other applications. 

   more » « less
2. Tuning magnetic confinement of spin-triplet superconductivity

   https://doi.org/10.1038/s41535-020-00270-w  

   Lin, Wen-Chen; Campbell, Daniel J.; Ran, Sheng; Liu, I-Lin; Kim, Hyunsoo; Nevidomskyy, Andriy H.; Graf, David; Butch, Nicholas P.; Paglione, Johnpierre (December 2020, npj Quantum Materials)

   null (Ed.)

   Abstract Electrical magnetoresistance and tunnel diode oscillator measurements were performed under external magnetic fields up to 41 T applied along the crystallographic b axis (hard axis) of UTe 2 as a function of temperature and applied pressures up to 18.8 kbar. In this work, we track the field-induced first-order transition between superconducting and magnetic field-polarized phases as a function of applied pressure, showing suppression of the transition with increasing pressure until the demise of superconductivity near 16 kbar and the appearance of a pressure-induced ferromagnetic-like ground state that is distinct from the field-polarized phase and stable at zero field. Together with evidence for the evolution of a second superconducting phase and its upper critical field with pressure, we examine the confinement of superconductivity by two orthogonal magnetic phases and the implications for understanding the boundaries of triplet superconductivity. 

   more » « less
3. Electronic phase separation and magnetic-field-induced phenomena in molecular multiferroic (ND4)2FeCl5⋅D2O

   https://doi.org/https://doi.org/10.1103/PhysRevB.98.054407  

   W. Tian, H. B. (January 2018, Physical review. B, Condensed matter)

   Electronic phase separation has been increasingly recognized as an important phenomenon in understanding many of the intriguing properties displayed in transition metal oxides. It is believed to produce fascinating functional properties in otherwise chemically homogenous electronic systems, e.g., colossal magnetoresistance manganites and high-Tc cuprates. While many well-known electronically phase-separated systems are oxides, it has been argued that the same phenomenon should occur in other electronic systems with strong competing interactions. Here we report the observation of electronic phase separation in molecular (ND4)2FeCl5⋅D2O, a type-II multiferroic. We show that two magnetic phases, one of which is commensurate and the other of which is incommensurate, coexist in this material. Their evolution under applied magnetic field produces emergent properties. In particular, our measurements reveal a field-induced exotic state linked to a direct transition from a paraelectric/paramagnetic phase to a ferroelectric/antiferromagnetic phase, a collective phenomenon that hasn't been seen in other magnetic multiferroics. 

   more » « less
4. Giant and negative magnetoresistances in conical magnets in the nonequilibrium Boltzmann equation approach

   https://doi.org/10.1088/1361-648X/ad80f1  

   Rivlis, Raz; Zadorozhnyi, Andrei; Dahnovsky, Yuri (October 2024, Journal of Physics: Condensed Matter)

   Abstract We study magnetotransport in conical helimagnet crystals using the nonequilibriun Boltzmann equation approach. Spin dependent magnetoresistance exhibits dramatic properties for high and low electron concentrations at different temperatures. For spin up electrons we find negative magnetoresistance despite only considering a single carrier type. For spin down electrons we observe giant magnetoresistance due to depletion of spin down electrons with an applied magnetic field. For spin up carriers, the magnetoresistance is negative, due to the increase in charge carriers with a magnetic field. In addition, we investigate the spin dependent Hall effect. If a magnetic field reaches some critical value for spin down electrons, giant Hall resistance occurs, i.e. Hall current vanishes. This effect is explained by the absence of spin down carriers. For spin up carriers, the Hall constant dramatically decreases with field, due to the increase in spin up electron density. Because of the giant spin dependent magnetoresistance and Hall resistivity, conical helimagnets could be useful in spin switching devices. 

   more » « less
5. Successive Phase Transitions and Multiferroicity in Deformed Triangular-Lattice Antiferromagnets Ca ₃ MNb ₂ O ₉ (M=Co, Ni) with Spatial Anisotropy

   https://doi.org/10.1149/2162-8777/ac7254  

   Huang, Q.; Lee, M.; Choi, E. S.; Ma, J.; Dela Cruz, C.; Zhou, H. D. (June 2022, ECS Journal of Solid State Science and Technology)

   We constructed the magnetic field-temperature phase diagrams of new quasi-two-dimensional isosceles triangular lattice antiferromagnets (TLAF) Ca 3 MNb 2 O 9 (M=Co, Ni) from dc and ac magnetic susceptibilities, specific heat, dielectric constant, and electric polarization measurements on single crystalline samples. Ca 3 CoNb 2 O 9 with effective spin-1/2 Co 2+ ions undergoes a two-step antiferromagnetic phase transition at T N1 = 1.3 K and T N2 = 1.5 K and enters a stripe ordered state at zero magnetic field. With increasing field, successive magnetic phase transitions, reminiscent of the up-up-down ( uud ) and the oblique phases, are observed. The dielectric constant of Ca 3 CoNb 2 O 9 shows anomalies related to the magnetic phase transitions, but clear evidence of ferroelectricity is absent. Meanwhile, Ca 3 NiNb 2 O 9 with spin-1 Ni 2+ ions also shows a two-step antiferromagnetic transition at T N1 = 3.8 K and T N2 = 4.2 K at zero field. For Ca 3 NiNb 2 O 9 , the electric polarization in the magnetic ordered phases was clearly observed from the pyroelectric current measurements, which indicates its coexistence of magnetic ordering and ferroelectricity. 

   more » « less