Bulletin of the American Physical Society
Mid-Atlantic Section Meeting 2021
Volume 66, Number 18
Friday–Sunday, December 3–5, 2021; Rutgers University, New Brunswick, New Jersey
Session B01: Quantum Matter: Magnetism |
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Chair: Sang Wook Cheong, Rutgers University Room: 201A |
Friday, December 3, 2021 5:00PM - 5:12PM |
B01.00001: Multiple Ferroic Orders and Toroidal Magnetoelectricity in a Chiral Magnet BaCoSiO$_{4}$ Xianghan Xu, Fei-Ting Huang, Sang-Wook Cheong BaCoSiO$_{4}$ adopts a $P$6$_{3}$ lattice at RT, which is structurally chiral and polar. The magnetic Co$^{2+}$ ions form a triangular lattice, and an extremely intriguing “toroidal moment plus canted ferromagnetic moment” type magnetic structure appears below 3.2 K, which holds magnetic chirality as well. Our comprehensive electron microscopy study of high-quality BaCoSiO$_{4}$ single crystal grown by the Laser Floating Zone technique reveals a mono global chirality from the prototypic lattice, as well as various local chirality consisting of stripy polar domains and ferro-rotational domains. If the magnetic chirality is fixed by the structurally mono global chirality, applying magnetic field along c can create net toroidicity, and off-diagonal linear ME effect could be observed, and vice versa. The orientation-dependent ME effect is measured on oriented single crystals at 2 K. The data show that BaCoSiO$_{4}$ has both diagonal response $P_{c}(H_{c})$ and off-diagonal response $P_{a\ast }(H_{a})$. This off-diagonal response is consistent with the theoretical scenario that a toroidal moment along $c$ axis with in-plane $H$ induces in-plane $P$ perpendicular to $H$. The observable toroidal ME effect suggests that the magnetic chirality is fixed by the structurally mono global chirality. The resulting mono magnetic chirality ensures the effective tuning of toroidal moment by field along $c$. "-3 to -1 to 1 to 3" toroidal moment metamagnetic transitions are demonstrated, and the induced $P$ triples in a consistent manner. BaCoSiO$_{4}$ is a unique playground for studying the multifaceted coupling of structural and magnetic ferroic orders. [Preview Abstract] |
Friday, December 3, 2021 5:12PM - 5:48PM |
B01.00002: Magnetic avalanche of non-oxide conductive domain walls Invited Speaker: Istvan Kezsmarki Conductive domain walls have been exclusively observed in oxides, where off-stoichiometry and defects often hamper the domain wall conductivity and render the walls immobile and thus curtail their usefulness and flexibility. In this talk, we will show the giant conductivity of domain walls in the non-oxide multiferroic GaV$_{4}$S$_{8}$, investigated by macroscopic transport as well as scanning probe microscopy experiments. We observe fascinating architectures of ribbon- and folded sheet-like conductive domain walls emerging in the polar rhombohedral state of GaV$_{4}$S$_{8\, }$below its Jahn-Teller transition at T$_{JT} \quad =$ 45 K. Besides the giant negative magnetoresistance inherent to these conductive domain walls, their high conductivity is exploited to trigger unprecedentedly large changes of the bulk resistance via on-demand magnetic or electric conversions between multi- and mono-domain states. Such a transformation to the insulating mono-domain state through an avalanche-like domain-wall expulsion process leads to an abrupt conductance changes as large as eight orders of magnitude. These unique properties demonstrate that non-oxide ferro-electrics can be the source of novel phenomena beyond the realm of oxide electronics. [Preview Abstract] |
Friday, December 3, 2021 5:48PM - 6:24PM |
B01.00003: Magneto-Raman studies of magnons in 2D magnetic materials and quantum magnet CoTiO3 Invited Speaker: Thuc Mai Raman spectroscopy is a versatile technique due to its non-destructive nature, surface sensitivity, and low energy sensitivity, down to a few meV. These attributes naturally lead to the use of Raman scattering as a probe of quantized spin waves, or magnons, in magnetic materials. Our custom-built magneto-Raman system comprises of a triple grating spectrometer, a magneto cryostat with optical access, and multiple continuous wave laser lines that cover the entire visible spectrum. We first explore the magnetic excitations in two-dimensional (2D) magnetic materials. Magnetic excitations in van der Waals (vdW) materials, especially in the 2D limit, are an exciting research topic from both the fundamental and applied perspectives. From the antiferromagnetic magnon gap excitation in FePS3[1] to the hybridization of a two-magnon excitation with the phonons in MnPSe3[2], our magneto-Raman studies revealed a rich set of magnetic excitations in the family of vdW magnet MPX3, where M is a transition metal, P is phosphorous, and X is Sulfur or Selenium. Second, we look at our unpublished results on an exciting quantum material, CoTiO3. We follow the evolution of the Brillouin Zone center excitations of not only the optical magnon, but also several spin-orbit excitations across the magnetic transition temperature. Our experiment provides a high-resolution measurement of these magnetic modes at k$=$0. Additionally, by applying the external magnetic field along the c-axis and along a hexagonal axis, we reveal the highly anisotropic g-factor of these magnetic excitations. Surprisingly, we measure the beginning of a magnetically induced crossing between the acoustic and optical magnon. Our results are supported by density functional theory (DFT) and linear spin wave theory (LSWT), as well as being consistent with inelastic neutron scattering experiments in the literature. [1] McCreary et al. Phys. Rev. B 101, 064416 (2019) [2] Mai et al. SCIENCE ADVANCES. 29 Oct 2021. Vol 7, Issue 44 [Preview Abstract] |
Friday, December 3, 2021 6:24PM - 7:00PM |
B01.00004: Electronic and Magnetic Properties of the Topological Kagome Metal YMn$_6$Sn$_6$ Invited Speaker: Rebecca Dally YMn$_6$Sn$_6$ (Y166) exhibits topologically protected characteristics, which are unusual given the underlying centrosymmetric crystal lattice. The structure is composed of Mn atoms on a kagome lattice in the $ab$-plane, which are then stacked along the $c$-axis with the layers separated either by three Sn layers or a mixed Y and Sn layer. This stacking pattern has an important magnetic implication, mainly, that within a unit cell there are two unequal interlayer exchange pathways with opposite signs. A short-lived collinear antiferromagnetic phase, with an onset of $T_N \approx 340$ K, transitions below 333 K to a double-flat-spiral magnetic structure due to the exchange competition. At elevated temperatures and modest in-plane magnetic fields, a topological Hall effect (THE) emerges, [1,2] despite a null scalar spin chirality; dynamic chiral fluctuations are thought to be responsible, thus making Y166 a prototype material for a fluctuation based THE mechanism. [1] The application of the in-plane magnetic field also leads to a magnetic-temperature phase diagram that is quite complex. We have identified five magnetic phases via bulk measurements, and through theoretical and neutron diffraction studies were able to solve the magnetic structures for all but one of the in-field phases. [1,3] We also present a result obtained via a polarized neutron diffraction study. [3] Unexpectedly, unequal chiral domain populations of the zero-field spiral state were found despite the underlying centrosymmetric crystal symmetry. This could be a significant finding as it implies that the spiral state can energetically favor one domain over the other, possibly in a controlled manner. This is another example, along with the THE, of Y166 displaying unusual behavior for a structure with inversion symmetry.\\ 1. Ghimire et al. $Sci. Adv.$, \textbf{6}, eabe2680 (2020).\\ 2. Wang, et al. $Phys. Rev. B$, \textbf{103}, 014416 (2021).\\ 3. Dally et al. $Phys. Rev. B$, \textbf{103}, 094413 (2021). [Preview Abstract] |
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