Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session B48: General Magnetism I |
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Sponsoring Units: GMAG Room: Mile High Ballroom 1A |
Monday, March 3, 2014 11:15AM - 11:27AM |
B48.00001: Renormalization of spin-rotation coupling Mamoru Matsuo, Jun'ichi Ieda, Sadamichi Maekawa We show the enhancement of the spin-rotation coupling due to the interband mixing[1]. The Bloch wave functions in the presence of mechanical rotation are constructed with the generalized crystal momentum which includes a gauge potential originating from the rotation. Using the Kane model, the renormalized spin-rotation coupling is explicitly derived. As a result of the renormalization, the rotational Doppler shift in electron spin resonance, the mechanical torque on an electron spin, and the spin current generation due to elastic deformation[2] will be strongly enhanced. [1] M. Matsuo, J. Ieda and M. Maekawa, Phys. Rev. B87, 115301 (2013). [2] M. Matsuo, J. Ieda, K. Harii, E. Saitoh and M. Maekawa, Phys. Rev. B87, 180402(R) (2013). [Preview Abstract] |
Monday, March 3, 2014 11:27AM - 11:39AM |
B48.00002: Ab Initio $\alpha\rightarrow\epsilon$ Transition Barrier in Shocked Iron Michael P. Surh, Babak Sadigh An ab initio study is presented of the $\alpha\rightarrow\epsilon$-like transition in single crystal iron under uniaxial strain (Kalantar, et. al., Phys. Rev. Lett. 95 075502 (2005)). First-principles ground state DFT calculations for ordered-spin phases predict a magnetostructural transition from ferromagnetic (FM) to an antiferromagnetic (AFM) phase at a uniaxial strain similar to experiment. However, the calculated stress is higher than is inferred from the shock. DFT also predicts a significant energy barrier for the expected atomic shuffle transition from bcc to hcp. In contrast, the experimental kinetics are consistent with a barrier-free or small-barrier transformation path. It is possible that the neglect of thermal spin disorder in the DFT calculations explains these discrepancies. To study this, the spin and atomic order are artificially separated, assuming that the atomic motion is adiabatic on spin time-scales. A Heisenberg-like Hamiltonian is fit to DFT energies of different ordered magnetic phases, and magnetic free energies are calculated for fixed atomic coordinates by Monte Carlo methods. This model predicts a significantly smaller elastic constant than DFT for the FM ground state, and it reduces the transition energy barrier versus ground state values. [Preview Abstract] |
Monday, March 3, 2014 11:39AM - 11:51AM |
B48.00003: Time-reversal invariant U(1) spin liquids in three dimensions Chong Wang, Senthil Todadri We study possible quantum U(1) spin liquids in three dimensions with time-reversal symmetry. We find there are in total eight such states, distinguished by the properties of their emergent electric/magnetic charges. Various aspects of these states will be discussed, including their spin wave-functions and relevance to pyrochlore spin ices. [Preview Abstract] |
Monday, March 3, 2014 11:51AM - 12:03PM |
B48.00004: Magnetic Phase Diagram of the Classical Kitaev-Heisenberg (KH) Model Craig Price, Natalia Perkins In this work, we numerically study the low-temperature magnetic properties of the Kitaev-Heisenberg model using classical Monte-Carlo simulations. Due to the discreteness of the KH model caused by the Kitaev interaction while in zero magnetic field, the model is magnetically ordered at low temperatures for all non-zero values of the Kitaev interaction except at two special points. The ordered phase is stabilized entropically by an order-by-disorder mechanism where thermal fluctuations of classical spins select collinear magnetic states that point along a cubic direction. We computed the H-T phase diagrams of the KH model for different orientations of the magnetic field and estimated the saturation field and its directional dependence in each phase. The low-temperature magnetic phase diagram is significantly modified both by the presence of external magnetic fields and the field's orientation with respect to cubic axes. In the Kitaev limit, the external field continuously changes the classical ground-state manifold of the geometrically frustrated classical Kitaev, thus it stabilizes different magnetic states at different strengths of the magnetic field. Our results can be used to understand the physics of Li$_2$IrO$_3$ and Na$_2$IrO$_3$ in an applied magnetic field. [Preview Abstract] |
Monday, March 3, 2014 12:03PM - 12:15PM |
B48.00005: ABSTRACT WITHDRAWN |
Monday, March 3, 2014 12:15PM - 12:27PM |
B48.00006: Unusual physical behaviors of strongly correlated rare earth dialuminides Durga Paudyal, V.K. Pecharsky, K.A. Gschneidner, Jr. We present electronic, magnetic, and magnetostructural behaviors of rare earth dialuminides calculated by first principles. Total energy calculations show that CeAl$_{2}$ and EuAl$_{2}$ adopt antiferromagnetic ground states while dialuminides formed by other magnetic lanthanides have ferromagnetic ground states. The magnetic moment of CeAl$_{2}$ indicates that the 4f orbital moment of Ce in CeAl$_{2}$ is quenched. Eu in EuAl$_{2}$ and Yb in YbAl$_{2}$ are divalent. PrAl$_{2}$ exhibits a tetragonal distortion near ferromagnetic transition. HoAl$_{2}$ shows a first order magnetostructural transformation while DyAl$_{2}$ shows a second order transformation. The dialuminides formed by Nd, Tb, and Er are simple ferromagnet without additional anomalies in the ferromagnetic state. SmAl$_{2}$ orders ferromagnetically with less than 1 $\mu_{\mathrm{B}}$ indicating the cancellation of 4f spin moment by its orbital counterpart. Due to substantially high 4f crystal field splitting TmAl$_{2}$ shows 4f spin magnetic moment lower than expected. [Preview Abstract] |
Monday, March 3, 2014 12:27PM - 12:39PM |
B48.00007: Superconducting instability of a non-magnetic metallic band in an antiferromagnetic background Fernando Reboredo In superconducting cuprates there is experimental consensus that, for low doping, holes occupy a band primarily formed by the $p_x$ and $p_y$ oxygen orbitals in the CuO2 planes. However, it is very difficult to determine whether this band is formed by $\sigma$ or a $\pi$ bonds with the $d$ orbitals of copper. In electron doped cuprates, the location of the carriers less clear. Most ab-initio methods based in a mean field approach lack of the accuracy required to determine the location of the carriers introduced by doping due to errors in exchange, correlation and self-interaction. Nevertheless, these methods have been used to support models that consider only one Cu orbital and the $\sigma$ oxygen bonds. In this talk we consider what could happen if the carriers go elsewhere and discuss attempts to determine the location of these carriers with diffusion Monte Carlo. It is shown that if the holes occupy the $\pi$ bonds or the electrons remain centered at the cation outside the planes, a non-magnetic metallic band would form. In the presence of an antiferromagnetic background this band will be coupled to the planes by the exchange interaction in second order, developing a superconducting instability similar to the one described by BCS theory. [Preview Abstract] |
Monday, March 3, 2014 12:39PM - 12:51PM |
B48.00008: Ferromagnetism and stability of three-fermion clusters in two-dimensional lattices Pavel Kornilovitch A three-body spin-$\frac{1}{2}$ fermion problem with on-site repulsion and nearest-neighbor attraction is solved on a one-dimensional chain and on a two-dimensional square lattice by discretizing the Schroedinger equation in momentum space. Energies of bound complexes (trions) and their binding conditions are obtained for total spins S = 1/2 and S = 3/2. In the S = 1/2 sector in one dimension, a narrow but finite parameter region is identified where the ground state consists of a stable fermion pair and an unbound fermion [EPL, 103, 27005 (2013)]. In the S = 1/2 sector in two dimensions, a much wider region of pair stability is found. The stability is attributed to the formation of a centrifugal barrier for the third fermion. In the S = 3/2 sector in two dimensions, trions are found to form before triplet pairs indicating ``Borromean'' coupling. In the strong-attraction limit in two dimensions, the system transitions from an S = 1/2 ground state to a ferromagnetic S = 3/2 ground state in agreement with the Nagaoka theorem for a four-site plaquette. [Preview Abstract] |
Monday, March 3, 2014 12:51PM - 1:03PM |
B48.00009: Spin-spin interaction in the bulk of topological insulators Liang Chen, Jinhua Sun, Hai-Qing Lin We apply mean-field theory and Hirsch-Fye quantum Monte Carlo method to study the spin-spin interaction in the bulk of three-dimensional topological insulators. We find that the spin-spin interaction has three different components: the longitudinal, the transverse and the transverse Dzyaloshinskii-Moriya-like terms. If the chemical potential is located in the bulk gap of topological insulators, the spin-spin interaction decays exponentially due to the Bloembergen-Rowland interaction. And the longitudinal correlation is antiferromagnetic, the transverse correlations is ferromagnetic and the transverse Dzyaloshinskii-Moriya-like correlation is suppressed if the distance between magnetic impurities is sufficient large. When the chemical potential is in the conduction or valence band, the spin-spin interaction follows power law decay, and isotropic ferromagnetic interaction dominates in short separation limit. [Preview Abstract] |
Monday, March 3, 2014 1:03PM - 1:15PM |
B48.00010: MBE Growth of Si/MnGe Quantum Dot Superlattice with Curie Temperature beyond 400 K Tianxiao Nie, Xufeng Kou, Yabin Fan, Jianshi Tang, Shengwei Lee, Murong Lang, Chia-Pu Chu, Liang He, LiTe Chang, Kang L. Wang The realization and application of spintronic devices would be boosted dramatically if room-temperature ferromagnetism could be integrated into semiconductor nanostructures, especially when compatible with the mature silicon technology. Here, a Si/MnGe superlattice with quantum dots well aligned in the vertical direction was successfully grown by molecular beam epitaxy. Magnetic measurements found that the superlattice structure exhibited a Curie temperature beyond 400 K, which is attributed to the presence of Mn-doped quantum dot nanostructures. Such unique Si/MnGe superlattice sets a new stage for strengthening ferromagnetism due to the enhanced hole-mediation by quantum confinement, which has the potential to realize the room-temperature spin filed-effect transistor devices with lower power dissipation and low variability. [Preview Abstract] |
Monday, March 3, 2014 1:15PM - 1:27PM |
B48.00011: First-principles evidence of Mn moment canting in hole-doped Ba$_{1-2x}$K$_{2x}$Mn$_{2}$As$_{2}$ James Glasbrenner, Igor Mazin The compound BaFe$_{2}$As$_{2}$ is the proptotypical example of the 122 family of high-$T_{c}$ Fe-based superconductors that crystallize in the ThCr$_{2}$Si$_{2}$ structure. Isostructural compounds can be formed by replacing Fe with another transition metal; using Mn produces the material BaMn$_{2}$As$_{2}$. Despite its lack of superconductivity, the material is interesting in its own right. Recent experimental studies have shown that hole-doping the compound by substituting K for Ba leads to metallic behavior and a spontaneous, weak, in-plane magnetization, which was attributed to the holes fully polarizing independent of the Mn moments, producing half-metallic behavior. However the observed in-plane magnetization can also be understood as a small canting of the Mn moments. Using density functional theory, we demonstrate that a Mn moment canting occurs upon hole-doping the compound. We argue that this is due to the competition between the super- and double exchange interactions, which we support using a simple tight-binding model of the superexchange-double exchange interaction and the Andersen Force Theorem. Our calculations also rule out an in-plane polarization of As holes as an explanation for the in-plane magnetization. [1]J. K. Glasbrenner and I. I. Mazin, arXiv:1311.1537 [Preview Abstract] |
Monday, March 3, 2014 1:27PM - 1:39PM |
B48.00012: ABSTRACT WITHDRAWN |
Monday, March 3, 2014 1:39PM - 1:51PM |
B48.00013: Magnetic force microscopy of magnetic domains in UMn$_{2}$Ge$_{2}$ Morgann Berg, Alex de Lozanne, Ryan E. Baumbach, Jeehoon Kim, Eric D. Bauer, Joe D. Thompson, Filip Ronning UMn$_{2}$Ge$_{2}$, a distant cousin to the heavy-fermion compound URu$_{2}$Si$_{2}$, is a ternary intermetallic compound with a tetragonal crystal structure of type ThCr$_{2}$Si$_{2}$ and with space group I4/mmm. Local U and Mn moments in UMn$_{2}$Ge$_{2}$ order on their respective sublattices at temperatures near 100 and 380 K, respectively. Previous high-pressure x-ray diffraction and Kerr rotation angle measurements point to structural and magnetic phase transitions that reflect the competition between U and Mn spins at low temperatures. As U moments order with a reduction in temperature, they are predicted to align the Mn moments along the c-axis, altering the anisotropy of the material and the easy axis direction. A reduction of inter-atomic distances between the U and Mn atoms is also projected to induce hybridization between uranium 5f and manganese 3d states, leading to a delocalization of magnetic moments and reduction in magnetization. We use a variable temperature atomic force microscope in magnetic force microscopy (MFM) mode to obtain some initial images of magnetic domains in UMn$_{2}$Ge$_{2}$. Room temperature MFM images display branching magnetic domains with uniaxial anisotropy. [Preview Abstract] |
Monday, March 3, 2014 1:51PM - 2:03PM |
B48.00014: Non-hysteretic colossal magnetoelectric effect in a collinear antiferromagnet Yoon Seok Oh, Sergey Artyukhin, Jun Jie Yang, Vivien Zapf, Jae Wook Kim, David Vanderbilt, Sang-Wook Cheong Electric field control of magnetization has attracted lots of attention because of its potential applications for magnetoelectric devices such as memory, sensors and oscillators, as well as a fundamental interest. Recently, large magnetoelectric responses have been reported in various magnetoelectric systems. Most of the colossal magnetoelectric effects are in response to domain wall motion associated with the phase coexistence and metastability at the 1st order phase transition. This nature leads to hysteretic behavior of the magnetoelectric response. In applications for sensors and oscillators, the hysteresis plays a role of detrimental side-effect such as low precision, drift and asymmetric oscillation. In this talk, we demonstrate non-hysteretic colossal magnetoelectric effect in a collinear antiferromagnet and discuss colossal magnetoelectric response of magnetization as well as polarization associated with the continuous spin-flop transition. [Preview Abstract] |
Monday, March 3, 2014 2:03PM - 2:15PM |
B48.00015: Influence of pressure and chemical substitution on samarium-cobalt permanent magnets Scott McCall, Jason Jeffries, Jonathon Lee, Patrick Huang The magnetic properties of a material are generally sensitive to its crystal structure, particularly its interatomic spacing. This spacing can be adjusted through application of external pressure and by chemical substitution. Measurements on the magnetic and thermodynamic properties of samarium cobalt permanent magnets are reported as a function of applied pressure and chemical substitution on the cobalt site. The effects of these two tuning parameters will be compared and discussed. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
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