Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session B19: Skyrmions in Oxide Materials and HeterostructuresInvited
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Sponsoring Units: GMAG Chair: Kai Liu, Georgetown University Room: 207 |
Monday, March 2, 2020 11:15AM - 11:51AM |
B19.00001: Harsh condition scanning probe microcopy vs. imaging detection of new magnetic structures and their topological protection Invited Speaker: Qingyou Lu The scanning probe microscope has atomic resolution, which is a revolution in microscopy. But, it is sensitive to even weak vibration or sound (V/S) and requires well designed V/S isolation. However, many important researches must be performed in harsh conditions such as in ultra-strong water-cooled magnet (WM), cryogen-free (dry) superconducting magnet, dilution refrigerator or reactive solution. To this end, we have achieved high quality atomic resolution images in harsh and ultra-harsh conditions. Finally, we are successful in obtaining high clearance atomic resolution images in a WM [Ultramicroscopy 205(2019)20], dry magnet [Nano Res. 8(2015)3898] and active/reactive solution [Nano Res. 9(2016)2551; Nanoscale 8(2016)15142]. We will report these achievements as well as their applications in the imaging detections of new and weak magnetic structures with topological protection such as magnetic skyrmions in ultra-thin (only 5 layers of unit cells) oxide heterostructures BTO/SRO [Nature Mater. 17(2018)1087], artificially fabricated skyrmions [Adv. Funct. Mater. (2019)1907140], structural domain walls [Adv. Mater. 30(2018)1805353], multiply ordered electronic crystals [ACS Appl. Mater. Inter. 10(2018)20136] and phase competition in re-entrance process [Nature Comm. 6(2015)8980]. |
Monday, March 2, 2020 11:51AM - 12:27PM |
B19.00002: Skyrmions in Oxide Materials and Heterostructures Invited Speaker: Kang L. Wang Magnetic skyrmions are small swirling topological spin textures in either non-centrosymmetric |
Monday, March 2, 2020 12:27PM - 1:03PM |
B19.00003: Spin-Hall topological Hall effect in highly tunable Pt/ferrimagnetic-insulator bilayers Invited Speaker: Fengyuan Yang Electrical detection of topological magnetic textures such as skyrmions has been limited to conducting materials. Magnetic insulators offer key advantages for skyrmion technologies with high speed and low loss. We observe a prominent topological Hall effect in Pt/Tm3Fe5O12 bilayers, where the pristine Tm3Fe5O12 epitaxial films down to 1.25 unit cell thickness allow for tuning of topological Hall stability over a broad range from 200 to 465 K through atomic-scale thickness control [1]. Although Tm3Fe5O12 is insulating, the topological magnetic textures can be detected through a novel phenomenon: “spin-Hall topological Hall effect” (SH-THE), where the interfacial spin-orbit torques allow spin-Hall-effect generated spins in Pt to experience the unique topology of the underlying skyrmions in Tm3Fe5O12. This novel electrical detection phenomenon paves a new path for utilizing a large family of magnetic insulators in future skyrmion technologies. |
Monday, March 2, 2020 1:03PM - 1:39PM |
B19.00004: Observation of room temperature polar skyrmions Invited Speaker: Ramamoorthy Ramesh Complex topological configurations are a fertile playground to explore novel emergent phenomena and exotic phases in condensed-matter physics. For example, the recent discovery of polarization vortices and the associated complex-phase coexistence and response under applied field in superlattices of (PbTiO3)n/(SrTiO3)n suggests the presence of a complex, multi-dimensional system capable of exotic physical responses. I will describe the discovery of polar skyrmions in a lead-titanate layer confined by strontium-titanate layers by atomic-resolution scanning transmission electron microscopy (STEM). Phase-field modeling and second-principles calculations reveal that the polar skyrmions have a skyrmion number of +1 and resonant soft X-ray diffraction experiments show circular dichroism confirming chirality. Such nanometer-scale polar skyrmions exhibit a strong signature of negative permittivity at the surface of the skyrmion, which is furthermore highly tunable with an electric field. They are a new state of matter and electric analogs of magnetic skyrmions, and may be envisaged for potential applications in information technologies. I will attempt to describe the exciting observations we have made through many collaborations. |
Monday, March 2, 2020 1:39PM - 2:15PM |
B19.00005: Nonequilibrium Skyrmion Dynamics under Oscillating Magnetic Fields Invited Speaker: Christina Psaroudaki We extend earlier studies on the quantum propagation of a skyrmion in chiral magnetic insulators [1], to include the effects of time periodic magnetic field gradients on skyrmion dynamics [2]. The unavoidable coupling of the external field to the magnons gives rise to time-dependent dissipation for the skyrmion, with measurable consequences on the skyrmion path. These ac fields act as a net driving force on the skyrmion via its own intrinsic magnetic excitations. We generalize the standard quantum theory of dissipation to include the stochastic effects of the driven bath on the skyrmion dynamics. We address the stochastic effects of the quantum driven bath on the skyrmion propagation [3], and provide a generalized version of the nonequilibrium fluctuation-dissipation relation for externally driven reservoirs. We also predict a novel fast thermal activation for the mean-square displacement that scales quadratically with temperature in the experimentally accessible low-temperature regime. |
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