Bulletin of the American Physical Society
2024 APS March Meeting
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session Z25: Magnetization and Spin Dynamics: Theory II |
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Sponsoring Units: GMAG Chair: David Dahlbom, Oak Ridge National Laboratory Room: 101F |
Friday, March 8, 2024 11:30AM - 11:42AM |
Z25.00001: Effect of thermal noise on the field-assisted spin-orbit-torque-driven dynamics in Mn_{3}Sn Siyuan Qian, Ankit Shukla, Shaloo Rakheja D0_{19}-Mn_{3}Sn, an antiferromagnet (AFM) with a non-collinear spin structure, has recently been investigated for its large anomalous Hall effect, low-current dynamics, and as a source of spin-polarized current. Thin films of Mn_{3}Sn, when grown epitaxially on MgO (110) [001], experience a uniaxial tensile strain. Consequently, the bulk six-fold anisotropy changes to a two-fold perpendicular magnetic anisotropy (PMA). Prior numerical works have examined SOT-driven deterministic dynamics in PMA Mn_{3}Sn in the presence of a symmetry-breaking magnetic field at . They find the final steady-state to depend on the magnitude of the input current, , with respect to two critical currents (J_{c}^{th1} and J_{c}^{th2}). The magnetic octupole switches from one stable state to another for J_{c} > J_{c}^{th1} whereas it exhibits chiral rotations, whose frequency could be tuned from MHz-GHz, if J_{c} > J_{c}^{th2}. These works, however, do not consider the role of thermal noise either in the equilibrium state or during the dynamics. Therefore, in our work, we solve coupled LLG equations in the presence of a thermal field. Consequently, the equilibrium states show a Gaussian distribution around ϕ_{oct} =±π/2. We find the standard deviation to be directly related to the temperature, T, and inversely related to the volume, Vand the saturation magnetization, M_{s}. The octupole exhibits stochastic dynamics and switches (oscillates) even for J_{c} < J_{c}^{th1} (J_{c} < J_{c}^{th2}). We expect the insights of our investigation to be useful to both experimentalists and device designers. |
Friday, March 8, 2024 11:42AM - 11:54AM |
Z25.00002: Spin and Charge Pumping in the presence of Spin-Orbit Coupling at ferromagnet or antiferromagnet resonance Jalil Varela Manjarres One of the primary mechanisms used in spintronics is the transfer of angular momentum by means of pure spin current pumping, which can occur due to the magnetization dynamics produced by stationary precession of the localized magnetic moment under ferromagnetic or antiferromagnetic resonance and in the absence of any applied voltage. This is a well-known phenomenon that occurs due to the absorption of low-power microwaves of frequency $omega_0$ under resonance conditions. Consequently, as predicted by the literature, the spin current along the precession axis is proportional to $omega _0$, while the x and y components oscillate harmonically at the resonance frequency. Additionally, the charge current can only be zero when there is no inversion symmetry; This opens the opportunity to manipulate and produce THz frequencies through the Antiferromagnetic resonance phenomena. We reexamine the spin pumping problem through two exact general formalisms: a time-dependent non-equilibrium Green's functions (TDNEGF) and the Floquet formalism combined with the stationary Non equilibrium Green's function (NEGF) formalism, thereby predicting unforeseen spin pumping features in a system of localized moments precessing within a Ferromagnetic (FM) or Antiferromagnetic (AFM) resonance, in which the conduction electrons are subjected to the effects of spin-orbit coupling. It was observed that both spin and charge current components oscillate in integer multiples of the characteristic frequency. Besides that, it has been found that the frequency cutoff increases following the magnitude of the spin-orbit parameter, reaching a value of ($N_{max}approx 11$) in a FM or AFM system in one dimension and even larger values ($N_{max}approx 25$) in a 2D system defined on a honeycomb lattice. |
Friday, March 8, 2024 11:54AM - 12:06PM |
Z25.00003: Magnon spin current induced by electric field via Ahoronov-Casher effect Kazuki Yamamoto, Mikito Koshino, Takuto Kawakami We calculate the magnon current induced by an electric field via Ahoranov-Casher (AC) effect, applying non-equilibrium Green’s function method. |
Friday, March 8, 2024 12:06PM - 12:18PM |
Z25.00004: Light-induced weak ferromagnetism through nonlinear magnonic rectification Daniel Bustamante, Tom Kahana, Dominik M Juraschek, Wanzheng Hu We theoretically prove that a quasistatic magnetization can be induced by the coherent excitation of a chiral phonon mode. Such phonon mode can generate an effective magnetic field that gives way to a transient spin canting in a mechanism we call nonlinear magnonic rectification. This result is an example of light-induced weak ferromagnetism and provides a promising avenue for creating nonequilibrium spin configurations. |
Friday, March 8, 2024 12:18PM - 12:30PM |
Z25.00005: Resolving nonclassical magnon composition of a magnetic ground state via a qubit Anna-Luisa E Römling, Akashdeep Kamra, Carlos Sánchez Μuñoz, Alejandro Vivas-Viaña Recently gained insights into equilibrium squeezing and entanglement harbored by magnets point towards exciting opportunities for quantum science and technology, while concrete protocols for exploiting these are needed. Here, we theoretically demonstrate that a direct dispersive coupling between a qubit and a noneigenmode magnon enables detecting the magnonic number states' quantum superposition that forms the ground state of the actual eigenmode - squeezed-magnon - via qubit excitation spectroscopy. Furthermore, this unique coupling is found to enable control over the equilibrium magnon squeezing and a deterministic generation of squeezed even Fock states via the qubit state and its excitation. Our work demonstrates direct dispersive coupling to noneigenmodes, realizable in spin systems, as a general pathway to exploiting the equilibrium squeezing and related quantum properties thereby motivating a search for similar realizations in other platforms. |
Friday, March 8, 2024 12:30PM - 12:42PM |
Z25.00006: Theoretical analysis of multi-magnon Excitations in 2D Antiferromagnet probed by Resonant Inelastic X-ray Scattering (RIXS) SUBHAJYOTI PAL, Umesh Kumar, Prabhakar Prabhakar, Anamitra Mukherjee Resonant inelastic x-ray spectroscopy (RIXS) has emerged as an important tool to explore magnetism in two-dimensional (2D) antiferromagnet realized in strongly correlated materials. Here we consider the Heisenberg model with nearest and next nearest neighbor hopping relevant to the study of magnetic excitations of the cuprate family. |
Friday, March 8, 2024 12:42PM - 12:54PM |
Z25.00007: Spin dynamics simulations of spin wave spectrum of ferromagnetic monolayer CrI_{3} Xiuping Tao, Mckayla Dixon, Akeeya S Lucas Inelastic neutron scattering experiments show that magnons in bulk CrI_{3} present a two-band spin-wave dispersion, and the band crossings at the Brillouin zone corners are not observed. Instead, a finite gap between the two bands was reported. The microscopic origin of the gap and its very existence in the monolayer (ML) limit are still controversial. Using the Heisenberg spin model with parameters extracted from first-principles calculations, we perform spin dynamics simulations to study ML ferromagnetic honeycomb CrI_{3} and pay particular attention to its spin wave spectrum near high symmetry points, in an effort to examine whether the gap persists in the ML limit and, if it does, the size of it. |
Friday, March 8, 2024 12:54PM - 1:06PM |
Z25.00008: Magnetocaloric Behavior in 2D Magnets: A Dimensionality Perspective Lokanath Patra, Yujie Quan, Bolin Liao The incorporation of two-dimensional (2D) materials in magnetocaloric systems offers a state-of-the-art approach to enhance solid-state magnetic cooling for sustainable applications. However, the impact of dimensionality on the magnetocaloric performance of 2D magnets remains less understood. In this work, we employ density functional theory and atomic spin dynamics simulations to reveal a remarkable increase in the magnetocaloric effect (MCE) in ferromagnetic monolayers compared to bulk counterparts. This enhancement is attributed to the absence of interlayer exchange coupling, resulting in a lower transition temperature and a stronger dependence of the magnetization on temperature near their Curie temperatures. Furthermore, 2D ferromagnetic monolayers exhibit higher sensitivity to external magnetic fields and achieve saturation magnetization at lower applied field strengths, leading to larger magnetic entropy and adiabatic temperature changes. These findings provide valuable theoretical insights into MCE in 2D magnets and hold promise for advanced cooling and thermal management in compact nanodevices. |
Friday, March 8, 2024 1:06PM - 1:18PM |
Z25.00009: Reconstructing the spatial structure of quantum correlations with spectroscopy Allen O Scheie, Pontus Laurell, Elbio R Dagotto, David A Tennant, Tommaso Roscilde Quantum correlations are fundamental to many-body quantum physics, but are often difficult to experimentally probe. In this talk I show that the momentum-dependent dynamical susceptibility measured via inelastic neutron scattering enables the systematic reconstruction of quantum correlation functions, which express the degree of quantum coherence in the fluctuations of two spins at arbitrary mutual distance. Using neutron scattering data on the compound KCuF_{3} — a system of weakly coupled S=1/2 Heisenberg chains — and of numerically exact quantum Monte Carlo data, we show that quantum correlations possess a radically different spatial structure with respect to conventional correlations. Indeed, they exhibit a new emergent length of quantum-mechanical origin — the quantum coherence length — which is finite at any finite temperature (including when long-range magnetic order develops). Moreover, we show theoretically that coupled Heisenberg spin chains exhibit a form of quantum monogamy, with a trade-off between quantum correlations along and transverse to the spin chains. These results highlight real-space quantum correlators as an informative, model-independent means of probing the underlying quantum state of real quantum materials. |
Friday, March 8, 2024 1:18PM - 1:30PM |
Z25.00010: Quantum-critical scaling in the Mn-based kagome metal Sc_{3}Mn_{3}Al_{7}Si_{5} Yasuyuki Nakajima, Charuni Dissanayake, Kapila Kumarasinghe, Mark Tomlinson, Eun Sang Choi Kagome lattices can host a variety of exotic ground states, including quantum spin liquids and correlated phases associated with dispersionless flat energy bands. The Mn-based kagome metal Sc_{3}Mn_{3}Al_{7}Si_{5} crystalizes a hexagonal structure in which Mn ions form a kagome network, and shows unusual behavior in transport and thermodynamic properties [1]. Interestingly, a recent study, supported by theoretical calculations, has suggested the presence of orbital-selective flat-band-induced ferromagnetic fluctuations [2]. To elucidate the flat-band-induced ferromagnetic instability, we synthesized single crystals of Sc_{3}Mn_{3}Al_{7}Si_{5} and measured charge transport and heat capacity at very low temperatures. We observe no anomaly associated with long-range order in resistivity down to 15 mK and a logarithmic divergence in low-temperature heat capacity. The logarithmic divergence in heat capacity is strongly suppressed by magnetic fields, suggesting a crossover from non-Fermi-liquid to Fermi-liquid behavior, often observed in quantum critical metals. This anomalous crossover in heat capacity is well described by quantum-critical scaling. We will discuss the relationship between the quantum criticality and orbital-selective flat bands in the kagome metal Sc_{3}Mn_{3}Al_{7}Si_{5}. |
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