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 C40: Magnetization DynamicsFocus Live
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Sponsoring Units: GMAG DMP Chair: Vijaysankar Kalappattil, Colorado State University |
Monday, March 15, 2021 3:00PM - 3:36PM Live |
C40.00001: Ferrimagnetic thin film systems for spintronic THz emitters Invited Speaker: Manfred Albrecht THz radiation in the frequency range from 0.3 to 30 THz bridges the gap between electronic and optical frequencies. It has been used for probing and driving fundamental resonances in gaseous, liquid, and solid materials. However, it is still challenging to generate broadband THz radiation with sufficient power in a convenient way. Recently, a new type of an efficient THz emitter has been discovered, which is based on the inverse spin Hall effect [1,2]. These “spintronic” THz emitters typically consist of thin ferromagnetic (FM)/nonmagnetic metal bilayers which need to be excited by fs laser pulses. |
Monday, March 15, 2021 3:36PM - 3:48PM Live |
C40.00002: Voltage-Controlled Dynamic Modulation of Electromagnetic Response in Antiferromagnetic Materials at Terahertz Frequencies Xinyi Xu, Yuriy Semenov, Ki Wook Kim Antiferromagnetic materials have recently attracted interest due to advantages including high resonance frequencies up to terahertz, and the possibility of electrically modulating the magnetic properties such as the anisotropy makes them excellent candidates for energy-efficient devices. In this study, we theoretically applied such features on the dynamic manipulation of electromagnetic responses with a broad tunable spectral range. Dielectric antiferromagnets with strong magneto-electric/-elastic coupling were considered, which can achieve robust control of perpendicular magnetic anisotropy with less dissipation than the metallic counterparts. Theoretical analysis based on motion equation was used to derive the frequency-dependent permeability and the resonance frequency of antiferromagnets for different biaxial anisotropy profiles and incident electromagnetic wave polarizations. Numerical calculations adopting typical parameters indicated that the resonance frequency modulation reaches tens of percent in the sub-mm wavelength range, along with the corresponding permeability change. Application to specific devices such as a bandpass filter further illustrated the validity of the concept. |
Monday, March 15, 2021 3:48PM - 4:00PM Live |
C40.00003: Ferromagnetic Resonance in Permalloy film - Platinum/Cobalt Island Hybrid Systems Jeffrey Rable, Susan Kempinger, Yu-Sheng Huang, Michael CS Vogel, Axel F Hoffmann, Peter Schiffer, Nitin Samarth Nanomagnetic arrays in frustrated geometries, also known as artificial spin ice (ASI), have emerged both |
Monday, March 15, 2021 4:00PM - 4:12PM Live |
C40.00004: FMR Modes in Connected Kagome Artificial Spin Ice Ali Frotanpour, Justin S Woods, Lance Eric De Long Artificial spin ices (ASI) are typically periodic, 2-D lattices of sub-micron, ferromagnetic thin-film segments [1]. Each segment is elongated to attain a strong shape-anisotropy that induces single-domain, Ising-like spins. ASI lattices designed to exhibit frustration of the Ising dipole interactions (e.g., Kagome arrays). ASI exhibit complex dynamics that vary with lattice type and applied DC field orientation. We use broad-band ferromagnetic resonance (FMR) and micromagentic simulations to characterize FMR modes in connected, Kagome ASI that is complicated by additional short-range exchange interactions and domain walls within lattice vertices. We use a field protocol to set an ASI in a particular magnetization state. Generally, the highest-frequency FMR mode in ASI arises in segments whose Ising moment makes the smallest angle with the applied field [1]. In contrast, we show that control of the magnetization state of the vertices determine which segments resonate at the highest frequency. Our findings improve understanding of FMR modes in ASI and provide new guidelines for controlling resonance modes in magnonic devices. |
Monday, March 15, 2021 4:12PM - 4:48PM Live |
C40.00005: Coherent Sub-Terahertz Spin Pumping from an Insulating Antiferromagnet Invited Speaker: Enrique Del Barco Present STT-based devices rely on ferromagnetic materials as their active constituents. However, the flexibility offered by the intrinsic net magnetization and anisotropy for detecting and manipulating the magnetic state of ferromagnets also translates into limitations in terms of density (neighboring elements can couple through stray fields), speed (frequencies are limited to the GHz range), and frequency tunability (external magnetic fields needed). A new direction in the field of spintronics is to employ antiferromagnetic materials. In contrast to ferromagnets, where magnetic anisotropy dominates spin dynamics, in antiferromagnets spin dynamics are governed by the interatomic exchange interaction energies, which are orders of magnitude larger than the magnetic anisotropy energy, leading to the potential for ultrafast information processing and communication in the THz frequency range, with broadband frequency tunability without the need of external magnetic fields. |
Monday, March 15, 2021 4:48PM - 5:00PM Live |
C40.00006: Using magnetic tunnel junctions to probe quantum properties of materials Calvin Bales, Erick Garcia, Yiou Zhang, Gang Xiao, Vesna Mitrovic Magnetic tunnel junctions (MTJ) are ultra sensitive, low noise devices that can operate in extreme environmental conditions such as high electric and magnetic fields and low temperatures. MTJs can detect magnetic fields to picoTesla sensitivity, have spatial resolution on a relevant mesoscopic length scale and frequency sensitivity from DC to several GHz, and can operate in zero or finite applied electric or magnetic fields. In this talk, we will present modes in which MTJ based-sensors can be optimized to probe quantum properties of materials. |
Monday, March 15, 2021 5:00PM - 5:12PM Live |
C40.00007: Nanoscale Detection of Magnon Excitations with Variable Wavevectors Through a Quantum Spin Sensor Eric Lee-Wong, Ruolan Xue, Feiyang Ye, Andreas Kreisel, Toeno Van der Sar, Amir Yacoby, Chunhui Du Control and manipulation of pure spin currents in magnetic insulators has been a central focus of modern spintronic research. Building on the transformative nitrogen vacancy (NV) based quantum sensing platform, we have achieved local detection of a range of spin wave modes in magnetic insulator Y3Fe5O12 thin films over a 100-nanometer length scale. Through the multi-magnon scattering process, the excited spin waves generate fluctuating magnetic fields at the NV electron spin resonance frequencies, accelerating the relaxation of the NV spin. By measuring the variation of the emitted photoluminescence of the NV center, the detailed information of the magnon modes can be optically accessed, providing a unique window to reveal the local magnetic properties of the studied materials. Our findings highlight the significant opportunities offered by NV spin quantum sensors in exploring nanoscale spin dynamics of emergent spintronic systems. |
Monday, March 15, 2021 5:12PM - 5:24PM Live |
C40.00008: Probe and Control of Photo-excited Magnetization Precession in Co/Pd Multilayer Films Nicholas W Smith, Brenden A Magill, Rathsara Herath Mudiyanselage, Hiro Munekata, Giti Khodaparast Understanding the fundamental limits for ultrafast manipulation of magnetism in ordered spin systems is vital for the development of novel spin-based devices as well as very-efficient magneto-optical recording. In this talk, we present the dynamics of photo-excited precession of magnetization (PEPM) in Co/Pd multilayer films using time resolved magneto-optical Kerr effect (TRMOKE) for different pump fluences. Several Co/PD layers with the Co thicknesses ranging from 0.2 nm to 0.74 nm were measured in magnetic fields from 0 mT to 250 mT. PEPM relies on the effective field which is composed of the anisotropic field, demagnetization field, and the external field. We report on studies where we vary the excitation intensity, to probe the region in which rapid changes in the demagnetization field are the dominant effect for PEPM and the region of lower fluencies (< 10 mJ/cm2) where the anisotropic magnetic field in the multilayer thin film samples becomes the dominant effect for PEPM. These low fluencies allow us to better probe the effect of the in-plane and out of plane magnetic anisotropy on the amplitude of oscillation of PEPM. |
Monday, March 15, 2021 5:24PM - 5:36PM Live |
C40.00009: Magnetization and relaxation dynamics of core-shell magnetic nanoparticles over broad temperatures and frequencies Thinh Bui, Adam Biacchi, Eduardo de Lima Correa, Weston L Tew, Angela Hight Walker, Cindi L Dennis, Solomon Isaac Woods Magnetic nanoparticles (MNP) are becoming increasingly important as a tracer for non-invasive, in vivo imaging (e.g. MPI1), magnetic hyperthermia, and thermometry. For these applications, MNP tracers, observed under AC magnetic fields, are desired to exhibit large magnetization and thermosensitivity (temperature-dependent magnetization), factors which are governed by a complex set of parameters, including size, morphology, magnetic anisotropy, and saturation magnetization.2 Under AC driving fields, MNP response is affected by complex relaxation dynamics spanning broad timescales from seconds to nanoseconds.3 For response optimization, we chose bi-magnetic nanoparticles with core-shell morphology since their magnetic properties are tunable via the antiferromagnetic exchange coupling of the two magnetic phases. Here, we present magnetic characterization results for our synthesized doped ferrite core-shell nanoparticles over a range of temperatures (250-330 K), magnetic field amplitudes (0-20 mTRMS), and frequencies (DC-10 MHz) to quantify magnetic anisotropy, relaxation times, and hysteresis. |
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