Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session L40: Magnetism and Domain Structures in Complex OxidesFocus
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Sponsoring Units: GMAG DMP Chair: Elke Arenholz, Lawrence Berkeley National Laboratory Room: BCEC 208 |
Wednesday, March 6, 2019 11:15AM - 11:51AM |
L40.00001: Titanate pyrochlores: Growth of stoichiometric crystals below their melting points Invited Speaker: Seyed Koohpayeh The pyrochlore rare earth titanates (RE2Ti2O7) have been intensively studied experimentally and theoretically over the past two decades. In the field of magnetism, this class of materials is considered to be ideal hosts for archetypal geometrical frustration, which consists of the quantum spin ice, classical spin ice, and spin liquid behaviors. The energy scales for such magnetic interactions are low; therefore, these systems are expected to be very sensitive to small perturbations of all kinds, including non-stoichiometry and structural defects. In this talk, we report the effects that synthesis and growth conditions can have on the stoichiometry, defect formation, and physical properties. We also describe the process to grow high-quality and stoichiometric pyrochlore titanate single crystals at temperatures below their melting points by changing their composition using the traveling solvent floating zone technique (TSFZ). |
Wednesday, March 6, 2019 11:51AM - 12:03PM |
L40.00002: Topological structural defects and exotic magnetic behaviors in hexagonal TbInO3 and GdInO3 Jae Wook Kim, Xueyuen Wang, Fei-Ting Huang, Yazhong Wang, Y Li, Sang-Wook Cheong, Xuan Luo, Eundeok Mun, Xiaxin Ding, Vivien Zapf Geometrical frustration may induce highly degenerate ground states, complex spin configurations, or exotic ground states. One extreme example is the spin liquid, where magnetic ordering is suppressed even at zero temperature by quantum fluctuations. Spin liquids may host novel properties such as spinon excitations, majorana edge states, etc. Here, we report intriguing examples of coexisting topological ferroelectric domains and exotic magnetism in hexagonal rare-earth (R) indates such as TbInO3 and GdInO3. Geometric ferroelectricity is realized in hexagonal RInO3 and we have unveiled Z6 vortex domains associated with geometric ferroelectricity in TbInO3 and GdInO3, as similar to what has been observed in hexagonal manganites. On the other hand, magnetic properties vary upon different R ions. For example, GdInO3 shows a phase transition at low temperatures below 2.5 K whereas no signature of phase transition is observed for TbInO3. We suggest that the topological defects and ferroelectric domain walls serve as an intrinsic playground for the edge states that may exist in frustrated magnets. |
Wednesday, March 6, 2019 12:03PM - 12:15PM |
L40.00003: Imaging antiferromagnetic antiphase domain boundaries using magnetic Bragg diffraction phase contrast Valery Kiryukhin, Min Gyu Kim, Bin Gao, Sang-Wook Cheong, Hu Miao, Claudio Mazzoli, Andi Barbour, Stuart B Wilkins, Ian Keith Robinson, Mark Dean Manipulating magnetic domains is essential for many technological applications. Recent breakthroughs in Antiferromagnetic Spintronics brought up novel concepts for electronic device development. Imaging antiferromagnetic domains is of key importance to this field. Unfortunately, some of the basic domain types, such as antiphase domains, cannot be imaged by conventional techniques. Herein, we present a new domain projection imaging technique based on the localization of domain boundaries by resonant magnetic diffraction of coherent x rays. Contrast arises from reduction of the scattered intensity at the domain boundaries due to destructive interference effects. We demonstrate this approach by imaging antiphase domains in a collinear antiferromagnet Fe2Mo3O8, and observe evidence of domain wall interaction with a structural defect. This technique does not involve any numerical algorithms. It is fast, sensitive, produces large-scale images in a single-exposure measurement, and is applicable to a variety of magnetic domain types. |
Wednesday, March 6, 2019 12:15PM - 12:27PM |
L40.00004: Imaging scale-invariant magnetic textures in a strongly correlated oxide Jiarui Li, Jonathan Pelliciari, Abraham Levitan, Claudio Mazzoli, Sara Catalano, Forrest Simmons, Jerzy T. Sadowski, Marta Gibert, Erica Carlson, Jean-Marc Triscone, Stuart B Wilkins, Riccardo Comin The electronic ground state of correlated electron systems, often manifests a granular texture across a broad range of length scales. Antiferromagnetic order is a common instability of these materials, however, its nanoscale spatial organization has not been systematically studied. In this talk, I will present our recent result using a resonant soft X-ray scattering nanoprobe to image the bulk magnetic landscape in NdNiO3 thin films. Our measurements provide direct evidence for a highly textured magnetic fabric, that further exhibits return memory effects across the Neel transition. The scale-free distribution of antiferromagnetic domains and its non-integral dimensionality, together reveal an unprecedented magnetic fractal geometry near criticality, which reflects the interplay between electronic correlations and an intrinsic local parameter. Our observations expose new essential details of the nanoscale anatomy of strongly correlated electronic systems. |
Wednesday, March 6, 2019 12:27PM - 12:39PM |
L40.00005: Capturing Dynamics of Incommensurate Antiferromagnetic Domains with Coherent Soft X-ray Scattering John Bowlan, Richard L Sandberg, Vivien Zapf, Xiaxin Ding, Shizeng Lin, Colby Walker, Benjamin A Pound, Nara Lee, Young Jai Choi, Andi Barbour, Wen Hu, Stuart B Wilkins, Claudio Mazzoli The observation of antiferromagnetic (AFM) domains and the dynamics of their interfaces remains an elusive problem. The physical origin and dynamics of AFM domains are different from ferromagnetic domains and are largely unexplored. In this work, we have studied the frustrated AFM, Lu2CoMnO6, with the brilliant, coherent, soft X-ray flux of the 23ID-1 beamline at NSLS-II [1]. Lu2CoMnO6 is a double perovskite with frustrated AFM order leading to incommensurate ordering and dynamic time scales ranging from seconds to days [2-4]. We have probed the AFM domain structure and dynamics of this material with X-ray photon correlation spectroscopy (XPCS). The motion of the domains is revealed by the motion of a speckle pattern in the scattered X-ray beam. We observed faster domain fluctuations below onset of hysteresis at (35K) and explained these observations within the Axial Next-Nearest-Neighbor Ising (ANNNI) model. |
Wednesday, March 6, 2019 12:39PM - 12:51PM |
L40.00006: Magnetic Domain wall resistance in Half-metallic CrO2 Lijuan Qian, Wenzhe Chen, Gang Xiao The half-metallic CrO2 is experimentally confirmed to have the highest spin polarization of nearly 100%. It is an ideal system to study magnetic domain-wall resistance (DWR), which differs from the resistance (or resistivity) inside a single-domain. We design and prepare a CrO2 epitaxial nanostructure with an asymmetrical weak link to localize a single DW, using the techniques of chemical vapor deposition and selective-area growth. The weak link design provides us the capability to generate /annihilate a single DW by applying a moderate/strong reversing magnetic field. By contrasting the resistance between a single-domain state and a DW state under zero field, we obtain the domain wall resistance in half-metallic CrO2. Using the Levy-Zhang model of DWR and simulated domain wall contour, we further obtain the spin asymmetry ratio between resistivities in the two spin channels. The ratio, 4256 ± 388 at 5.0 K, is 2 to 3 orders larger than that of conventional ferromagnetic metals, attesting the half-metallicity of CrO2. |
Wednesday, March 6, 2019 12:51PM - 1:03PM |
L40.00007: Domain reversal dynamics and avalanches in a model insulating Ising ferromagnet Daniel Silevitch, Christopher Tang, Thomas F Rosenbaum 100 years ago, Barkhausen’s noise experiments provided evidence for discrete domains within ferromagnets and magnetization reversal occurring as a set of discrete events. By characterizing individual avalanche events, the underlying mechanisms for domain reversal can be studied. Many materials show a drag effect which appears in the statistical distribution of avalanche event shapes. In typical metallic ferromagnets, this drag is believed to be due to eddy currents induced during magnetization reversal. Whether this is only significant source of drag is an open question which we address by studying the model Ising system LiHo0.65Y0.35F4, an insulating rare-earth, dipole-coupled ferromagnet with TC of 0.98 K. The LiHoxY1-xF4 family combine strong quantum fluctuations, random-field pinning, and a lack of eddy currents, extending the study of domain dynamics to an entirely new regime. We find symmetrical scaled distributions near TC, indicative of a drag-free environment. By contrast, strong asymmetries appear for long-duration events at lower temperatures, suggesting the presence of drag without eddy currents. A thermal-driven crossover between random-field effects and a quantum-fluctuation regime suggests that the latter act as the source of this additional drag mechanism. |
Wednesday, March 6, 2019 1:03PM - 1:15PM |
L40.00008: Domain Structure and Reversal Dynamics of Magnetoelectric Antiferromagnets Arun Parthasarathy, Shaloo Rakheja The single domain state of magnetoelectric (ME) antiferromagnet like Cr2O3 can be switched isothermally at room temperature by simultaneous application of electric and magnetic fields (He, et al., Nat. Comm. 2010; Kosub, et al., Nat. Comm. 2017). However, studies pertaining to switching dynamics, especially in thin-film systems, have been limited. |
Wednesday, March 6, 2019 1:15PM - 1:27PM |
L40.00009: Non-Reciprocal Directional Dichroism of THz Radiation in LiCoPO4: Read-out of Magnetoelectric Domains Toomas Room, Urmas Nagel, Sandor Bordacs, Jakub Vit, Istvan Kezsmarki, Judit Romhanyi, Karlo Penc, Vilmos Kocsis, Yusuke Tokunaga, Yasujiro Taguchi, Yoshinori Tokura Magnetoelectric (ME) effect in multiferroic materials is the cornerstone of new electronic devices allowing the electric field control of magnetization. Here we demonstrate the optical read-out of magnetoelectric domains in LiCoPO4 exploiting the absorption difference between ME domains [Kocsis et al., PRL121, 057601 (2018)]. Domains absorb differently because of non-reciprocal directional dichroism of spin wave resonances coupled to electric polarization. Single ME domain can be selected by poling with crossed electric and magnetic fields from the magnetically disordered state. |
Wednesday, March 6, 2019 1:27PM - 1:39PM |
L40.00010: Inhomogeneous magnetic order in T’-La4Ni3O8 Oscar Bernal, Douglas E. MacLaughlin, Gerald D Morris, Lei Shu, Cheng Tan, Jian Zhang, Zhaofeng Ding, Kevin Huang, Viktor V. Poltavets We report a muon spin rotation (μSR) study of the magnetic properties of the cuprate-analog nickelate La4Ni3O8. The crystal structure of this compound involves square planar NiO2 layers, potentially isoelectronic (Ni1+) to the Cu2+O2 layers of the cuprates. The material has a magnetic phase transition at 105 K, the structure of which has remained elusive. Zero-field μSR confirms the antiferromagnetic nature and commensurate character of this transition, and sheds light on the most likely configuration of Ni spins below the Néel temperature. Comparison of spectra of observed muon precession frequencies to lattice calculations of Ni dipolar fields at candidate muon stopping sites suggests a spin configuration consistent with the stripe charge order observed previously by x-ray diffraction [1]; in particular, the number of observed frequencies is greater than calculated for homogeneous spin structures without stripes. The frequency magnitudes suggest reduced Ni ordered moments of less than or about 0.5μB. We briefly discuss models of magnetic-stripe order based on alternative charge stripe configurations (cf. Ref. [1]) |
Wednesday, March 6, 2019 1:39PM - 1:51PM |
L40.00011: Unravelling Giant Exchange bias in the single layered Ruddlesden-Popper compound SrLaCo0.5Mn0.5O4: A combined studies of Experimental and Density Functional Theory RANJANA RANI DAS, Priyadarshini Parida, A.K. Bera, T. Chatterji, B.R K Nanda, Santhosh Nagappan Nair Discovering exotic magnetism due to competing magnetic interactions in layered perovskites with 3d hetero-species B-site ions has remained an intriguing topic with many unexplained features. Here we study Exchange bias (EB) phenomena in a single layered Ruddlesden-Popper SrLaCo0.5Mn0.5O4 using state of art measurement such as susceptibility, neutron diffraction and training effect along with density functional calculations. EB as large as ~5.5 kOe is observed in SrLaCo0.5Mn0.5O4 which is the highest ever found in any layered transition metal oxides including Ruddlesden-Popper series. Neutron diffraction measurements and together with dc magnetic measurements suggest formation of short range magnetic domains. By carrying out density functional calculations on several model configurations we propose that EB is originated at the boundary between Mn rich antiferromagnetic and Co rich ferromagnetic domains at the sub-nanoscale. Our analysis infers that presence of competing magnetic interactions is sufficient to induce exchange bias and thereby a wide range of materials exhibiting EB can be engineered. |
Wednesday, March 6, 2019 1:51PM - 2:03PM |
L40.00012: Potts transition in coupled XY models Victor Drouin-Touchette, Peter Orth, Premala Chandra, Piers Coleman, Tom Carl Lubensky Motivated by the long standing experimental mystery of the observation of a melting transition seemingly in the 3-state Potts universality class in thin films of liquid crystals, we revisit a model of coupled XY models. In these compounds, the interplay of the bond-orientational and herring-bone packing degrees of freedom, respectively invariant under rotation by π and by π/3, may lead to emergent discrete variables through the resulting anisotropic coupling. Using both large scale Monte-Carlo algorithms, with an adapted Wolff step and parallel tempering, and analytical methods, such as RG, we study the phase diagram of such a coupled XY model with global U(1) × Z3 symmetry. The presence of the discrete order can highly frustrate the possible binding of vortices, and we investigate how this non-trivial interaction can lead to unconventional arrangements of the vortices. Our extensive numerical study focuses on the regime where both XY variables are equally present, and we discuss the possibility of a 3-state Potts transition at higher temperature than the BKT transition, as well as the nature of the meeting point between the BKT and Potts phase transition. |
Wednesday, March 6, 2019 2:03PM - 2:15PM |
L40.00013: Inelastic Neutron Scattering Investigation of Quantum Order-by-disorder in Bi2CuO4 Bo Yuan, Nicholas Butch, Guangyong Xu, Young-June Kim
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