Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session R35: Magnetic Skyrmions in Novel Itinerant MagnetsInvited Live
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Sponsoring Units: GMAG Chair: Jiadong Zang, University of New Hampshire |
Thursday, March 18, 2021 8:00AM - 8:36AM Live |
R35.00001: Skyrmions and emergent electromagnetic responses in frustrated itinerant magnets Invited Speaker: Yoshinori Tokura Magnetic skyrmion can be formed in centrosymmetric frustrated lattice as well as in noncentrosymmetric lattice with Dzyalloshinskii-Moriya interaction. In particular, RKKY and related higher-order interactions in itinerant magnets with high crystal symmetries tend to stabilize the small-sized skyrmion lattice as well as competing helical-spin magnetic orders. Because of large emergent magnetic field via the high-density skyrmion lattice, gigantic topological Hall effect [1] and Nernst effect [2] are observed, e.g. for hexagonal Gd2PdSi3 with triangular-lattice net of magnetic Gd ions, indicating the importance of k-space picture of Berry curvature beyond the conventional real-space picture for the conventional large-sized skyrmion lattice systems. Among them, the breathing Kagome lattice of Gd moments in Gd3Ru4Al12 shows the skyrmion phase as well as the similarly short-pitch helical (spin screw) and transverse conical states [3]. The dynamics of these spin-spiral sates under the ac electric-current excitation can lead to the emergent electric field effect on the conduction electron, which in turn generates the emergent electromagnetic inductance (EEMI)[4]. Intriguing features and potentials of the EEMI are discussed in the light of the enhanced emergent electromagnetic responses in chiral magnets. |
Thursday, March 18, 2021 8:36AM - 9:12AM Live |
R35.00002: Skyrmion crystal from RKKY interaction mediated by 2D electron gas Invited Speaker: Cristian Batista We consider a C$_6$ invariant lattice of magnetic moments coupled via a Kondo exchange $J$ with a 2D electron gas (2DEG). The effective Ruderman-Kittel-Kasuya-Yosida interaction between the moments stabilizes a magnetic skyrmion crystal in the presence of magnetic field and easy-axis anisotropy. An attractive aspect of this mechanism is that the magnitude of the magnetic ordering wave vectors, $\bm{Q}_{\nu}$ ($\nu=1,2,3$), is dictated by the Fermi wave number $k_F$: $|\bm{Q}_{\nu} |=2k_F$. Consequently, the topological contribution to the Hall conductivity of the 2DEG becomes of the order of the quantized value, $e^2/h$, when $J$ is comparable to the Fermi energy $\epsilon_F$. |
Thursday, March 18, 2021 9:12AM - 9:48AM Live |
R35.00003: Zero-field magnetic skyrmions in model-type systems studied with STM Invited Speaker: Kirsten Von Bergmann Magnetic skyrmions can be stabilized in thin films by interface-induced Dzyaloshinskii-Moriya interactions that compete with exchange interactions. Such skyrmions can become lowest energy states in applied magnetic fields but are often only metastable configurations in zero magnetic field. Spin-polarized scanning tunneling microscopy is a powerful tool to characterize such magnetic textures down to the atomic scale [1]. |
Thursday, March 18, 2021 9:48AM - 10:24AM Live |
R35.00004: Quantum skyrmions in frustrated ferromagnets Invited Speaker: Achim Rosch We develop [1] a quantum theory of magnetic skyrmions and antiskyrmions in a spin-1/2 Heisenberg magnet with frustrating next-nearest neighbor interactions. Using exact diagonalization we show numerically that a quantum skyrmion exists as a stable many-magnon bound state and investigate its quantum numbers. We then derive a phenomenological Schrödinger equation for the quantum skyrmion and its internal degrees of freedom. We find that quantum skyrmions have highly unusual properties. Their bandwidth is exponentially small and arises from tunneling processes between skyrmion and antiskyrmion. The bandstructure changes both qualitatively and quantitatively when a single spin is added or removed from the quantum skyrmion, reflecting a locking of angular momentum and spin quantum numbers characteristic for skyrmions. Additionally, while for weak forces the quantum skyrmion is accelerated parallel to the force, it moves in a perpendicular direction for stronger fields. |
Thursday, March 18, 2021 10:24AM - 11:00AM Live |
R35.00005: Stabilization and observation of zero-field skyrmions in ferromagnetic and synthetic antiferromagnetic systems Invited Speaker: Vincent Cros Recently room-temperature skyrmions in ferromagnetic films and multilayers has been demonstrated and they show promise for encoding information bits in new computing technologies [1]. However, in ferromagnetic systems, the observation of skyrmions requires a substantial perpendicular field. Here we show that inserting a bias layer and utilizing interlayer electronic coupling, we successfully stabilize sub 100 nm skyrmions at zero field. A remaining challenge is that a transverse deflection of moving ferromagnetic skyrmions is present that hinder their efficient manipulation. Antiferromagnetic skyrmions could lift these limitations [4-5]. Here, we also show that room-temperature antiferromagnetic skyrmions can be stabilized in synthetic antiferromagnet (SAF) systems. Utilizing also a bias layer, we demonstrate by MFM [6] and by spin NV relaxometry [7] that the spin-spiral state obtained in a SAF system with vanishing perpendicular anisotropy can be turned into isolated antiferromagnetic skyrmions stable at zero field. These experimental results are completed with model-based estimations of their size and stability, showing that room-temperature stable antiferromagnetic skyrmions below 10 nm in radius can be anticipated in further optimized SAF systems [6]. Antiferromagnetic skyrmions in SAF systems may thus solve major issues associated to ferromagnetic skyrmions for low-power spintronic devices. |
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