28 research outputs found

    A hidden constant in the anomalous Hall effect of a high-purity magnet MnSi

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    Measurements of the Hall conductivity in MnSi can provide incisive tests of theories of the anomalous Hall (AH) effect, because both the mean-free-path and magnetoresistance (MR) are unusually large for a ferromagnet. The large MR provides an accurate way to separate the AH conductivity σxyA\sigma_{xy}^A from the ordinary Hall conductivity σxyN\sigma_{xy}^N. Below the Curie temperature TCT_C, σxyA\sigma_{xy}^A is linearly proportional to M M (magnetization) with a proportionality constant SHS_H that is independent of both TT and HH. In particular, SHS_H remains a constant while σxyN\sigma_{xy}^N changes by a factor of 100 between 5 K and TCT_C. We discuss implications of the hidden constancy in SHS_H.Comment: 5 pages, 4 figures. Minor change

    Complex Antiferromagnetic Order in the Metallic Triangular Lattice Compound SmAuAl4_4Ge2_2

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    The compounds LnLnAuAl4_4Ge2_2 (LnLn == lanthanide) form in a structure that features two-dimensional triangular lattices of LnLn ions that are stacked along the crystalline cc axis. Together with crystal electric field effects, magnetic anisotropy, and electron-mediated spin exchange interactions, this sets the stage for the emergence of strongly correlated spin and electron phenomena. Here we investigate SmAuAl4_4Ge2_2, which exhibits weak paramagnetism that strongly deviates from conventional Curie-Weiss behavior. Complex antiferromagnetic ordering emerges at TN1T_{\rm{N1}} == 13.2 K and TN2T_{\rm{N2}} == 7.4 K, where heat capacity measurements show that these transitions are first and second order, respectively. These measurements also reveal that the Sommerfeld coefficient is not enhanced compared to the nonmagnetic analog YAuAl4_4Ge2_2, consistent with the charge carrier quasiparticles exhibiting typical Fermi liquid behavior. The temperature-dependent electrical resistivity follows standard metallic behavior, but linear magnetoresistance unexpectedly appears within the ordered state. We compare these results to other LnLnAuAl4_4Ge2_2 materials, which have already been established as localized ff-electron magnets that are hosts for interesting magnetic and electronic phases. From this, SmAuAl4_4Ge2_2 emerges as a complex quantum spin metal, inviting further investigations into its properties and the broader family of related materials.Comment: 9 pages, 6 figure

    Field-Induced Magnetic States in the Metallic Rare-Earth Layered Triangular Antiferromagnet TbAuAl4_4Ge2_2

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    Magnetic frustration in metallic rare earth lanthanides (LnLn) with 4f4f-electrons is crucial for producing interesting magnetic phases with high magnetic anisotropy where intertwined charge and spin degrees of freedom lead to novel phenomena. Here we report on the magnetic, thermodynamic, and electrical transport properties of TbAuAl4_4Ge2_2. Tb ions form 2-dimensional triangular lattice layers which stack along the crystalline cc-axis. The magnetic phase diagram reveals multiple nearly degenerate ordered states upon applying field along the magnetically easy abab-plane before saturation. The magnetoresistance in this configuration exhibits intricate field dependence that closely follows that of the magnetization while the specific heat reveals a region of highly enhanced entropy, suggesting the possibility of a non-trivial spin textured phase. For fields applied along the cc-axis (hard axis), we find linear magnetoresistance over a wide range of fields. We compare the magnetic properties and magnetoresistance with an isostructral GdAuAl4_4Ge2_2 single crystals. These results identify TbAuAl4_4Ge2_2 as an environment for complex quantum spin states and pave the way for further investigations of the broader LnLnAuAl4_4Ge2_2 family of materials.Comment: 8 pages, 5 figure

    Non-saturating large magnetoresistance in semimetals

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    The rapidly expanding class of quantum materials known as {\emph{topological semimetals}} (TSM) display unique transport properties, including a striking dependence of resistivity on applied magnetic field, that are of great interest for both scientific and technological reasons. However, experimental signatures that can identify or discern the dominant mechanism and connect to available theories are scarce. Here we present the magnetic susceptibility (χ\chi), the tangent of the Hall angle (tanθH\tan\theta_H) along with magnetoresistance in four different non-magnetic semimetals with high mobilities, NbP, TaP, NbSb2_2 and TaSb2_2, all of which exhibit non-saturating large MR. We find that the distinctly different temperature dependences, χ(T)\chi(T) and the values of tanθH\tan\theta_H in phosphides and antimonates serve as empirical criteria to sort the MR from different origins: NbP and TaP being uncompensated semimetals with linear dispersion, in which the non-saturating magnetoresistance arises due to guiding center motion, while NbSb2_2 and TaSb2_2 being {\it compensated} semimetals, with a magnetoresistance emerging from nearly perfect charge compensation of two quadratic bands. Our results illustrate how a combination of magnetotransport and susceptibility measurements may be used to categorize the increasingly ubiquitous non-saturating large magnetoresistance in TSMs.Comment: Accepted for publication at Proc. Natl. Acad. Sci., minor revisions, 6 figure

    Generic magnetic field dependence of thermal conductivity in magnetic insulators via hybridization of acoustic phonons and spin-flip excitations

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    Magnetic insulators provide excellent playgrounds to realize a range of exciting spin models, some of which predict exotic spin ground states, and thermal transport properties have been taking center stage in probing the spin excitations. Despite the fact that acoustic phonons make the major contribution to heat conduction in a crystalline system, their interplay with magnetic excitations is often viewed as peripheral to the physics of interest, for instance as an inconvenient source of scattering or decoherence. Here, we present a comprehensive study on the longitudinal magneto-thermal transport in a paramagnetic effective spin-1/2 magnetic insulator CsYbSe2_2. We introduce a minimal model requiring only Zeeman splitting and magnetoelastic coupling, and use it to argue that hybridized excitations -- formed from acoustic phonons and localized spin-flip-excitations across the Zeeman gap of the crystal electric field ground doublet -- are responsible for a striking non-monotonic field dependence of longitudinal thermal conductivity. Beyond highlighting a starring role for phonons, our results raise the prospect of universal magneto-thermal transport phenomena in magnetic insulators that originate from simple features shared across many systems.Comment: 8 pages, 4 figure
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