Bulletin of the American Physical Society
2021 Annual Meeting of the APS Four Corners Section
Volume 66, Number 11
Friday–Saturday, October 8–9, 2021; Virtual; Mountain Daylight Time
Session K03: Electronic and Magnetic Phases and Their Properties |
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Chair: Minhyea Lee, University of Colorado Boulder |
Saturday, October 9, 2021 1:00PM - 1:24PM |
K03.00001: Designing high-performance superconductors with nanoparticle inclusions: comparisons to strong pinning theory Invited Speaker: Serena Eley The current carrying capacity $J_{\mathrm{c}}$ of type-II superconductors is severely limited by dissipation from the motion of vortices, magnetic flux lines that appear inside these materials upon exposure to sufficiently high magnetic fields. Incorporating nanoparticle inclusions into superconducting films is a well-established route for boosting $J_{\mathrm{c}}$ because defects can trap vortices. However, these inclusions reduce the overall superconducting volume and can strain the interlaying superconducting matrix, which can detrimentally reduce the critical temperature $T_{\mathrm{c}}$. Consequently, an optimal balance must be achieved between the nanoparticle density $n_{\mathrm{p}}$ and size $d$. Determining this balance requires garnering a better understanding of vortex-nanoparticle interactions, described by strong pinning theory. Here, we map the dependence of the critical current on nanoparticle size and density in (Y$_{\mathrm{0.77}}$Gd$_{\mathrm{0.23}})$Ba$_{\mathrm{2}}$Cu$_{\mathrm{3}}$O$_{\mathrm{7-\delta }}$ films in magnetic fields up to 35 T, and compare the trends to recent results from time-dependent Ginzburg-Landau simulations. We identify consistencies between the field-dependent critical current $J_{\mathrm{c}}(B)$ and expectations from strong pinning theory. Specifically, we find that that $J_{\mathrm{c}}\sim B^{\mathrm{-\alpha }}$, where $\alpha $ decreases from 0.66 to 0.2 with increasing density of nanoparticles and increases roughly linearly with nanoparticle size d/$\xi $ (normalized to the coherence length). At high fields, the critical current decays faster ($\sim B^{\mathrm{-1}})$ suggestive that each nanoparticle has captured a vortex. Lastly, we reveal that the dependence of the rate of thermally activated vortex motion (creep rate, $S)$ on nanoparticle size and density roughly mirrors that of $\alpha $, and compare our results to low $T$ nonlinearities in $S(T)$ that are predicted by strong pinning theory. [Preview Abstract] |
Saturday, October 9, 2021 1:24PM - 1:36PM |
K03.00002: Colossal magnetoresistance via avoiding fully polarized magnetization in the ferrimagnetic insulator Mn$_{3}$Si$_{2}$Te$_{6}$ Yifei Ni, Hengdi Zhao, Yu Zhang, Bing Hu, Itamar Kimchi, Gang Cao Colossal magnetoresistance is of great fundamental and technological significance and exists mostly in the manganites and a few other materials. Here we report colossal magnetoresistance that is starkly different from that in all other materials. The stoichiometric Mn$_{3}$Si$_{2}$Te$_{6}$ is an insulator featuring a ferrimagnetic transition at 78 K. The resistivity drops by seven orders of magnitude with an applied magnetic field above 9 T, leading to an insulator-metal transition at up to 130 K. However, the colossal magnetoresistance occurs only when the magnetic field is applied along the magnetic hard axis and is surprisingly absent when the magnetic field is applied along the magnetic easy axis where magnetization is fully saturated. The anisotropy field separating the easy and hard axes is 13 T, unexpected for the Mn ions with nominally negligible orbital momentum and spin-orbit interactions. Double exchange and Jahn-Teller distortions that drive the hole-doped manganites do not exist in Mn$_{3}$Si$_{2}$Te$_{6}$. The phenomena fit no existing models, suggesting a unique, intriguing type of electrical transport. [Preview Abstract] |
Saturday, October 9, 2021 1:36PM - 1:48PM |
K03.00003: Understanding the Short-Range Magnetic Correlations in MnTe Through Magnetic Pair Distribution Function Analysis Jacob Christensen, Benjamin Frandsen, Parker Hamilton, Raju Baral The antiferromagnetic semiconductor MnTe has attracted attention as both a high-performance thermoelectric and a candidate material for spintronics. The magnetic properties of MnTe play a crucial role in these applications. MnTe has a hexagonal layered structure in which magnetic Mn2$+$ spins order ferromagnetically within the plane and antiferromagnetically between planes below T$_{\mathrm{N}}=$ 307 K. Above T$_{\mathrm{N}}$, robust short-range magnetic correlations survive to high temperature. These correlations are a significant contributor to the high thermoelectric figure of merit zT in MnTe through a mechanism known as paramagnon drag. We present comprehensive atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering data collected from pure and doped MnTe powders, together with three-dimensional magnetic PDF data obtained from a single crystal of MnTe. These complementary data sets allow us to track the evolution of magnetic correlations from the long-range ordered state at low temperature to the short-range ordered state at high temperature. We present real-space magnetic models that reproduce the mPDF patterns with quantitative accuracy and discuss these results in the context of existing work on MnTe. [Preview Abstract] |
Saturday, October 9, 2021 1:48PM - 2:00PM |
K03.00004: Understanding the Magnetic Dynamics of MnTe using Muon Spin Relaxation Emma Zappala, Christiana Zaugg, Ben Frandsen MnTe is an antiferromagnetic semiconductor with potential technological applications as a high-performance thermoelectric material and a platform for spintronics. Its magnetic properties are crucial for both these applications. To understand the magnetic structure and dynamics better, we studied MnTe with muon spin relaxation ($\mu $SR), a technique that is highly sensitive to magnetic properties. We collected $\mu $SR data for a variety of temperatures through its magnetic transition of 307 K and fit mathematical functions to the resulting data, finding the appearance of two different short term oscillation frequencies that dampen as the material cools to around 100 K and reappear as it cools past 50 K. [Preview Abstract] |
Saturday, October 9, 2021 2:00PM - 2:12PM |
K03.00005: Thermoelectricity of the Compensated Semimetal NbSb${}_2$ Ian Leahy, Peter Siegfried, Andrew Treglia, Minhyea Lee With growing interest in the magnetothermoelectric properties of semimetals, it becomes pertinent to develop and analyze methods for classifying and modeling thermoelectric responses. We study the temperature and magnetic field dependence of the Seebeck and Nernst coefficients in the compensated semimetal NbSb${}_2$. At low temperatures and high fields we find that the Seebeck coefficient increases quadratically and the Nernst coefficient increases linearly as a function of field without signs of saturation up to 14T. We present a new analysis of thermoelectricity in highly compensated semimetals which shows that the nonsaturating magnetothermoelectric effects are related to the degree of compensation in the material. [Preview Abstract] |
Saturday, October 9, 2021 2:12PM - 2:24PM |
K03.00006: Fabrication of Thin Film Copper Selenate by PLD and Solid State Reaction David King, Jinke Tang, John Ackerman Cu$_{2}$OSeO$_{3}$ is a ferrimagnetic insulator with broken inversion symmetry. It is also a cubic helimagnet that hosts a magnetic skyrmion lattice, which makes it a potential material for spintronic applications. Previous research on Cu$_{2}$OSeO$_{3}$ has used single crystals and even investigations of thin layers of Cu$_{2}$OSeO$_{3}$ were done by milling down bulk single crystals. The skyrmion lattice phase is typically more stable in thin films than in the bulk. Additionally, thin films are more suitable for device applications. We have successfully fabricated actual thin film Cu$_{2}$OSeO$_{3}$. Here, we present results of using pulsed laser deposition (PLD) and subsequent solid state reactions to fabricate thin films of Cu$_{2}$OSeO$_{3}$. Data showing the film's crystallography and magnetic properties are presented. [Preview Abstract] |
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