Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session A57: Disordered Magnetic Materials |
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Sponsoring Units: GMAG Chair: Yuanpeng Zhang, Oak Ridge National Lab Room: Room 303 |
Monday, March 6, 2023 8:00AM - 8:12AM |
A57.00001: Evolution of structural and magnetic properties of Li4Cu1−xNixTeO6 (x = 0, 0.1, 0.2, 0.5, and 1) Ashiwini Balodhi, Brianna Billingsley, Tai Kong, Min Gyu Kim Li4CuTeO6 is a candidate material for quantum spin liquid (QSL) where the QSL state occurs primarily due to unavoidable anti-site disorder between Li+ and Cu2+ ions on triangular spin networks [1, 2]. We searched for nearby magnetic states and related compounds to elucidate the magnetic properties of Li4MTeO6 (M = Cu, Ni) system. Here, we present a comprehensive study of the structure and magnetic susceptibility of polycrystalline Li4Cu1-xNixTeO6 (x ≈ 0, 0.1, 0.2, 0.5, and 1) samples. We compare our results with previous studies on Li4CuTeO6 (S=1/2) [1, 2] and Li4NiTeO6 (S=1) [3] compounds. The structure analysis reveals that full incorporation of Ni (x =1) at the Cu site leads to a contraction in unit cell volume by around 1% and confirms the stabilization of Li4NiTeO6 on a honeycomb spin network of Ni2+ ions. Magnetic susceptibility measurements do not show any indication of onset magnetic order down to 2 K in any sample. The magnetic susceptibility follows the Curie-Weiss law at high temperatures for all samples, with a drastic decrease in Weiss temperature θcw from -145 K to -6.15 K for x = 0 and 1, respectively. Our observations support the exotic quantum nature of the magnetic ground states in this series of compounds, Li4Cu1-xNixTeO6. |
Monday, March 6, 2023 8:12AM - 8:24AM |
A57.00002: Disorder-Induced Fermi Arcs in Charge Density Wave Systems Hui Yang Recently, the five-layered Ba2Ca4Cu5 O10 (F,O)2 with lightly doped inner planes was studied in |
Monday, March 6, 2023 8:24AM - 8:36AM |
A57.00003: Spin Hall effect of vorticity Alexey A Kovalev, Edward Schwartz, Hamed Vakili, Moaz Ali Using mapping between topological defects in an easy-plane magnet and electrical charges, we study interplay between vorticity and spin currents. We demonstrate that the flow of vorticity is accompanied by the transverse spin current generation -- an effect which can be termed as the spin Hall effect of vorticity. We study this effect across the BKT transition and establish the role of dissipation and spin non-conservation in the crossover from spin superfluidity to diffusive spin transport. We show how the spin and vorticity currents can be modulated by changes in density of free topological defects, e.g., by using the Dzyaloshinskii-Moriya interactions or by tuning the in-plane magnet across the BKT transition by changing the exchange interaction, magnetic anisotropy, or temperature. Our results pave the way for low power computing devices relying on vorticity and spin flows. |
Monday, March 6, 2023 8:36AM - 8:48AM |
A57.00004: Theoretical and Experimental Investigation of CoMoFeAl and Related Compounds Gavin M Baker, Jax G Wysong, Shah Valloppilly, Paul M Shand, Pavel Lukashev, Parashu R Kharel Heusler compounds exhibiting high spin polarization at the Fermi level have attracted much attention with potential application in spintronic devices because of their tunable magnetic and electronic properties, and high Curie temperature much above room temperature. We have carried out joint theoretical and experimental investigations of such three Heusler compounds CoMoFeAl, CoMo0.5Fe1.5Al, and Co1.5Mo0.5FeAl. Our first-principle calculations show that all three compounds show either ferro- or ferrimagnetic order with CoMoFeAl, CoMo0.5Fe1.5Al exhibiting high spin polarization of almost 80%. The investigated samples were prepared using arc melting and high vacuum annealing. All the samples show cubic crystal structures with disorder. The parent compound CoMoFeAl shows ferromagnetic order with moderate saturation magnetization of 11.8 emu/g, and a Curie temperature of 480 K. The other two compounds, namely, Co1.5Mo0.5FeAl and CoMo0.5Fe1.5Al, show ferrimagnetic order with slightly high saturation magnetizations of 62 emu/g and 54 emu/g, respectively, and substantially higher Curie temperatures close to 1000 K. These results indicate that the investigated compounds may have magnetic and spintronic applications where moderate magnetization and high Curie temperatures are desired. |
Monday, March 6, 2023 8:48AM - 9:00AM |
A57.00005: First-principles investigation of high-entropy magnetic recording media dinesh bista Recent progresses in multi-element alloys with high configurational entropy offer an exciting new arena to realize novel types of high anisotropy materials.1 In this work, we combine transition metal elements to design optimized high entropy alloys (HEAs) with high magnetic anisotropy energy (MAE) and moderate Curie temperature (Tc) towards applications in magnetic recording media.
We have used the “Questaal” package, owing to its incorporation of Coherent Potential Approximation (CPA), to study an equiatomic [FeCoCuMnNi]0.5Pt0.5 system, a L10-phase. The crystal has a stable ordered phase of body-centered tetragonal (BCT) lattice formed by five transition-metal elements randomly occupying the corner sites, while a Pt atom resides at the center. MAE of the equiatomic phase is found to be 1.28 meV per unit cell using LSDA functional. We have further explored the trend of MAE by varying the amount of five transition metal elements with certain constraints such that 50% of L10-phase system consist of [FeCoCuMnNi] while the central Pt-atom remains the same. Similarly, we have investigated the Curie temperature (Tc) when quantity of individual atoms in [FeCoCuMnNi] is changed under certain constraints. GGA and LDA+U functionals are also tested to corroborate the results with experiments. The extremely large parameter space emanated from constrained combination of 5 transition elements makes it logical to use some machine learning algorithm to detect any specific trend in MAE, Tc, and both. Our results show a promising approach toward achieving optimized HEA material with large MAE and moderate Tc, suitable for magnetic recording media applications.
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Monday, March 6, 2023 9:00AM - 9:12AM |
A57.00006: Probing local structure, intercalant disorder, and magnetism in FexNbSe2 Matthew Erodici, Daniel K Bediako, Thuc T Mai, Angela R Hight Walker Magnetically intercalated transition metal dichalcogenides (TMDs) represent a promising class of emergent quantum materials for ultralow-power applications based on the manipulation of electron spin. In particular, iron-intercalated niobium-based dichalcogenides (i.e. FexNbS2 and FexNbSe2) pose as exciting materials platforms for antiferromagnetic spintronics, yet insight into how the intercalant distribution varies across compositions remains unclear. Here, we investigate the interplay between composition, local structure, and the onset of intercalant superlattice formation in FexNbSe2 (x ≤ 0.25) using energy-dispersive X-ray spectroscopy, confocal Raman spectroscopy and x-ray diffraction. We observe the emergence of new Raman-active phonon modes with increasing iron intercalation and, in particular, prominent ultralow-frequency modes as x approaches 0.25, attributed to iron superlattice formation. Moreover, we probe the symmetries and temperature-dependent behavior of these new modes via polarization- and temperature-dependent Raman measurements and find an anomalous temperature response for one of the associated superlattice modes. Furthermore, we track the evolution of the Néel transition across iron concentrations and find a maximum TN ~ 130K as x approaches 0.25, signaling the importance of long-range intercalant superstructure on the robustness of magnetic ordering. |
Monday, March 6, 2023 9:12AM - 9:24AM |
A57.00007: Isolated Susceptibility and its applicability to state populations in LiY1-xHoxF4. Sean R Giblin, David Billington, Steve T Bramwell, Clara Cafolla-Ward The (quasi-static) isolated susceptibility is a fundamental component of any susceptibility measurement but can generally be neglected. Yet when cleanly measured, it would be a quantity of great interest as it is essentially a `spectroscopic' probe of quantum states and their populations, but one that is inaccessible to standard techniques like neutron scattering. We have realised that driving at 104 - 106 Hz is sufficient to reveal the isolated susceptibility in many systems. If the states are known (e.g. through knowledge of the spin hamiltonian) then populations can be measured, giving a direct characterisation of far-from equilibrium behaviour, while if populations are near to equilibrium, then quantum states can be visualised. In the latter case, the isolated susceptibility has the most structure when spin states are superposed: hence the probe can be used to quantify superposed states and to measure their state concurrence. Here we demonstrate the applicability of this model to LiY1-xHoxF4., demonstrate that in the dilute we are in the isolated regime and discuss the implications of this observation to experimental interpretations of the low temperature behaviour. |
Monday, March 6, 2023 9:24AM - 9:36AM |
A57.00008: Disorder-induced ferrimagnetism in MnxCoGe films Brett MacNeil, Theodore L Monchesky, David Kalliecharan, Jason McCoombs, Marc Cormier, Laurent Molino We report on the observation of ferrimagnetism in Ni2In-type MnxCoGe films grown by magnetron sputtering for 0.8 ≤ x ≤ 2.5. The ferrimagnetic behavior is observed in contrast to the ferromagnetism reported for bulk Ni2In-type MnCoGe, which we attribute to the presence of defects. In the Mn-deficient samples, these defects arise from atomic disorder, whereas for the Mn-rich samples, the excess Mn is driven onto the Co or Ge sites. For lower values of x, the concentration of antisite defects increases and leads to a compensation point in the temperature-dependent magnetization (N or V-type ferrimagnetic behavior). Density-functional theory calculations explain the origin of the ferrimagnetism through antiferromagnetic coupling between Mn antisite defects and the Mn on the Mn-sites. Mean-field modeling supports the analysis and provides an estimate of the evolution of effective exchange parameters with Mn concentration. |
Monday, March 6, 2023 9:36AM - 9:48AM |
A57.00009: Magnetic-field symmetry breaking in spin glasses Ilaria Paga Time-reversal symmetry is spontaneously broken in spin glasses below their glass temperature. Under such conditions, the standard assumption about the equivalence of the most standard protocols (i.e. no big difference between switching the field on or off, as it is sometimes said) is not really justified. In fact, we show here that the spin-glass coherence length behaves differently in the zero-field-cooled (ZFC, magnetic field is turned on) and thermoremanent-magnetization (TRM, magnetic field is turned off) protocols. This conclusion is reached through experiments, carried out on two CuMn single-crystal samples, and through massive simulations on the Janus~II dedicated supercomputer. In agreement with the predictions of a simple dynamical model that assumes that the ultrametric tree of states survives the switching-on of the magnetic field, we conclude that (all parameters being kept equal) the spin-glass coherence length is larger in the ZFC protocol. This has implications for the extended principle of superposition, which, while holding at H = 0, breaks down for finite magnetic fields. Preliminary simulation results support this observation. |
Monday, March 6, 2023 9:48AM - 10:00AM |
A57.00010: Magnetic properties of diluted hexaferrites Logan B Sowadski, Sean Anderson, Cameron J Lerch, Julia E Medvedeva, Thomas Vojta Recent experimental observations of the magnetic properties of the diluted hexagonal ferrite PbFe12-xGaxO19, have remained a puzzle. Specifically, the dependence on the Ga concentration of the magnetic phase boundary and the saturation magnetization disagree with theoretical predictions. These earlier theories assume a uniform distribution of the Ga ions over all lattice sites. However, ab-initio density-functional calculations suggest a strong preference among the Ga ions towards the 12k sublattice, the most populous of the five Fe sublattices. Motivated by these calculations, we perform large-scale Monte Carlo simulations for a Heisenberg model with non-uniform vacancy distribution. With appropriately chosen Ga concentration in each sublattice, the simulation results are in excellent agreement with both the magnetic phase boundary and the saturation magnetization observed in recent experiments on the ferrite. This suggests the non-uniformity of the distribution of Ga impurities to be the main reason for the unusual magnetic properties held by PbFe12-xGaxO19. We also perform calculations for the individual sublattice magnetizations and their behavior as the system approaches the magnetic phase boundary at different Ga concentrations and different temperatures. |
Monday, March 6, 2023 10:00AM - 10:12AM |
A57.00011: Exploring a Magnetic Phase Transition in Amorphous FeGe Using X-ray Scattering. Ryan Tumbleson, Emily M Hollingworth, ARNAB SINGH, Ahmad Us Saleheen, Margaret R McCarter, David Raftrey, Sophie A Morley, Stephen D Kevan, Peter Fischer, Frances Hellman, Sujoy Roy The rich phase diagram of crystalline B20 FeGe, which hosts skyrmions, spin helices, and conical helices, arises due to the competition between the Heisenberg exchange interaction, which favors collinear spins, and the Dzyaloshinskii-Moriya interaction (DMI), which favors an angle between adjacent spins. Broken inversion symmetry in the crystalline structure is typically considered to be the origin of DMI. Amorphous FeGe has no well-defined crystalline lattice but still exhibits DMI and hosts magnetic spin textures. In this talk, I present results from resonant X-ray scattering studies on a magnetic phase transition in amorphous FeGe between an ordered stripe phase and a disordered paramagnetic phase. |
Monday, March 6, 2023 10:12AM - 10:24AM |
A57.00012: Strong Evidence that the Paramagnetic-Spin Glass Transition in a Magnetic Field is a Crossover Gregory G Kenning An understanding of the nature of the paramagnetic to spin glass phase transition has been lacking due to and interplay between time, temperature and magnetic-field, and the lack of a directly observable correlation length scale. In this paper we present TRM data that ties the characteristic time scales (associated with the growth of spin glass correlations) with the temperature, as the spin glass transition temperature is approached from below T<0.97 Tg. As a function of temperature in a fixed magnetic field, we have found a crossover timescale tco. For tco spin glass correlations are observed to grow whereas for t>tco, correlations can grow to the length scale associated with the tco timescale, but no larger. We have analyzed the structure of the crossover line for magnetic fields ranging from 9.6 G to 96 G. The magnetic field suppresses the growth of correlations. The data strongly suggests that in a magnetic field the spin glass phase transition is a dynamic crossover, while in zero field there is likely a phase transition. The Droplet Model (Phys. Rev. B 38, 373) qualitatively predicts this behavior. |
Monday, March 6, 2023 10:24AM - 10:36AM |
A57.00013: Extracting free-energy landscape of AgMn spin glass thin films with 1/f resistance fluctuations Kan-Ting Tsai, E. Dan Dahlberg, Raymond Orbach The temperature dependent 1/f noise in AgMn (12 at.%) thin films with multiple thicknesses (15, 20, 40, 60, 80, 100nm) is reported. The noise measurement provides the unique ability to probe the fundamental dynamics of a spin glass in zero field below the glass temperature. There is a significant increase in the magnitude of the noise in the spin glass state. Analysis of the temperature dependent exponent provides information on the energy barrier distribution and height which are related to the spin glass correlation length. We compare our results with those made previously on CuMn (13.5 at.%) thin films of similar thicknesses1 and observe a similar trend of the increase of the barrier height with respect to thickness, but with relatively lower values for AgMn as compared to CuMn. |
Monday, March 6, 2023 10:36AM - 10:48AM |
A57.00014: Magnetic field symmetry breaking in spin glasses Raymond L Orbach Time reversible symmetry is spontaneously broken in spin glasses below their transition temperature, Tg. Under such conditions, the standard assumption about the equivalence of switching the magnetic field on or off is not justified. We show that the growth of the spin glass coherence length [ξ(t,tw;H), where tw is the aging time] behaves differently between the zero-field-cooled (ZFC, magnetic field turned on) and the thermoremanent magnetization (TRM, magnetic field turned off) protocols.This is shown through experiments, carried out on two CuMn single crystals, and through massive simulations on the Janus II dedicated supercomputer. In agreement with the predictions of a simple dynamical model that assumes that an ultrametric tree of states survives the switching on of a magnetic field, we conclude that (all parameters being kept equal) ξ(t.tw;H) grows more slowly with time for a TRM protocol as compared to a ZFC protocol. This conclusion depends on the nature of the free energy barriers governing the time dependence of the protocols. If they increase linearly with diminishing overlap between the occupied states and the initial t = 0 state (increase of the Hamming distance), the two protocols yield identical time dependences for ξ(t,tw;H). If, however, they increase faster than linearly with diminishing overlap, then ξZFC(t,tw;H) > ξTRM(t,tw;H) for H > 0. This result has serious implications for the extended principle of superposition, MZFC(t,tw;H) + MTRM(t,tw;H) = MFC(t+tw;H), in the presence of a finite magnetic field. Here, MFC(t+tw;H) is the field cooled magnetization. In particular, it holds only at |
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